AtlasCopco Underground Construction

Atlas Copco Underground Construction

UNDERGROUND CONSTRUCTION

COMMITTED TO SUSTAINABLE PRODUCTIVITY

Printed matter no. 9851 3427 01

www.atlascopco.com

A global review of tunneling and subsurface installations

2015

We stand by our responsibilities towards our customers, towards the environment and the people around us. We make performance stand the test of time. This is what we call – Sustainable Productivity.

FIRST EDITION 2015

Contents

5

Foreword

7

Talking Technically

205

Case Studies

4

ATLAS COPCO MINING METHODS

Welcome to the

world of tunneling As global urbanization gains unprecedented momentum, tunneling expertise and rock excavation technology are playing a crucial role in shaping the future of our societies. Simply put, going underground is rapidly becoming the only viable option for meeting the infrastructure needs of the 21st century. According to UN estimations, 7 out of 10 people will be living in cities by 2050, meaning that a further 2.5 billion people will be added to the world's urban populations. The new city dwellers will all be dependent on the utilities and services that many of us take for granted: integrated transportation systems for road and rail, sufficient freshwater supplies, reliable sources of energy, functioning sewage and storm surge systems, to mention just a few examples of where tunnels provide key solutions.

“

Tunnels are the only option for tomorrow’s urban society.

”

What’s more, rules and regulations governing underground construction will only become stricter. Tunnels will need to be built and upgraded in the most environmentally sustainable, safe, responsible and economical way. It is a difficult challenge but one that an increasing number of tunneling professionals are conquering with groundbreaking results. Not only that, due to the demands of urbanization these tunnel designs are becoming increasingly complex. In this technical reference book, we turn a spotlight on the most common methods and practices in tunnel engineering – the backbone of all underground construction. As a leading supplier of rock excavation equipment for more than 140 years, Atlas Copco presents a holistic perspective of the industry, exploring a wide range of issues from market development, safety and operator training to environmental care and the role of technology and innovation. Whatever area of the industry you are working in or planning to join, we trust you will find this first edition of Underground Construction a valuable source of information and inspiration.

Sincerely, The Editorial and Application Specialists Team Atlas Copco Underground Rock Excavation

SAFETY FIRST Atlas Copco is committed to comply with or exceed all global or local rules and regulations for personal safety. However, some photographs in this reference book may show circumstances that are beyond our control. All users of Atlas Copco equipment are urged to think safety first and always use proper ear, eye, head and other protective equipment as required to minimize the risk of personal injury.

REFERENCE BOOK

5

6

ATLAS COPCO UNDERGROUND CONSTRUCTION – TALKING TECHNICALLY

Talking technically Tunneling overview 8 Tunnel excavation: A look back in history 18 The role of tunnels: Global market overview

Rock classification 26 Geology and why it matters 36 Geotechnical investigations 42 Rock mechanics

The tunneling process 48 52 56 58 62 66

Planning for new tunnels Management of projects Operator training and simulators Worksite infrastructure Maintenance Remote monitoring

Underground construction 68 Road and rail tunnels 80 90 98 104

Hydroelectric power plants Water and utility tunnels Oil and gas caverns Utilization of underground space

110 Radioactive waste deposits

Tunneling technique 116 Ventilation systems: Optimizing the air flow 120 130 138 144 150 158 164 170 174

High precision drilling Charging and blasting Data management tools The raiseboring complement Rock reinforcement Loading and haulage Grouting Diamond wire cutting Choice of methods

Trends in tunneling 186 Technical trends in tunneling 190 Safety 194 Energy consumption 200 Tunnel maintenance


7

Tunnel excavation for civil purposes became widespread from the mid-19 th century and onwards. Using brick lining as a permanent support was standard practice and it consisted of regular bricks with filling material behind the brick arch. This created an adhesion effect between the rock wall and roof and the load bearing arch.

A rich story written in stone

Man has been working underground for more than 5 000 years, and the lessons learned over the centuries, often in the face of overwhelming odds, have shaped the modern world of tunneling. Archaeological discoveries tell us that man has been working underground since the Stone Age. In those early days some 5 000 years ago, flint miners would use deer antlers as pickaxes to hack their way through limestone in search of flint. As they became more skilled, they learned to tunnel their way to flint deposits deep in the earth and to build underground rooms that became the hubs for smaller drifts. Ancient flint mines are not the only evidence that remains of early underground workings. There are many other examples

8

such as the Hallstatt salt mine in Austria that dates from 1 000 BC. Here, miners built tunnels with inclines of between 25 and 60 degrees in order to reach the salt, and then created drifts stretching as far as 400 m from the tunnel portals. Added to this are rooms measuring 12x12 m, evidence of mining operations that were carried out at depths of 100 m or more. Handheld tools were naturally used, and these were mostly bronze pickaxes with wooden handles, sledgehammers, chisels, and buckets for loading.


TUNNEL EXCAVATION: A LOOK BACK IN HISTORY

Completed in 1965, the Mont Blanc Tunnel in France proved a major success for Atlas Copco tunneling techniques. The tunnel was driven, from the Italian side, exclusively with light pusher leg fed rock drills and Coromant drill steels.

So now let’s jump forward a 1 000 years or so to the days of the Roman Empire. During this period, underground mining and construction only existed on a limited scale, and the Romans did not contribute much of any importance to the development of tunneling technique. The fire-setting method was known but not used, most likely due to the unpleasant fumes, smoke and heat that this would have caused in the already hot and stifling Mediterranean climate. The tools that were used were now made of iron, but beyond that, there was very little improvement in terms of technical development. With the exception of fire-setting, underground mining remained largely the same in most parts of the world during Roman times, right up until the 1700s when black powder, or gunpowder, came onto the scene. It was first used for blasting in Scandinavia at Nasafjäll in 1630, but in central Europe black powder was used as early as the 14th century.

William Bickford invented the encapsulated string fuse in 1830, which, when used together with black powder explosives, pioneered the safe detonation of rounds. Nitroglycerin, which was invented in the 1840s, was unpredictable, but this was solved by Alfred Nobel, who in 1865 invented a detonator that could control the ignition process. The demand for safer, more efficient rock blasting grew, and the first pneumatic rock drill was developed in 1857.

Fréjus – the start of modern tunneling

The construction of the Fréjus Tunnel that runs through the Alps between France and Italy is largely regarded as the start of modern tunneling technology. By 1870, the railway network had expanded dramatically across Europe as it had in the United States, but the mighty Alps still remained unconquered. To run a railway through the Alps would require long tunnels located deep beneath the mountains, and the technique needed to do that had not yet been mastered. It would


9

Tunneling overview

The drilling of blastholes by hand is also well documented. Two operators were required, one to strike the blows while the other took care of the rotation, feed and direction. In this way, blastholes, such as those at the Falun copper mine in Sweden, were drilled to a maximum depth of 1 m. Industrialization was then catapulted into the future on the back of several remarkable inventions. The famous race between the steam

engine prototypes – George Stephenson’s “Rocket” and John Ericsson’s “Novelty” – at Rainhill in England in 1829 was the start of the big railway era, and by 1850 about 8 000 km of railway had been built in England (see map in chapter Road and rail tunnels, p.76.)


The Sommeillers drill rig was used at the Fréjus Rail Tunnel from 1857 to 1871. Equipped with 4–9 pneumatic drills, the rig weighed 12 tonnes and was operated by a crew of 30–40 people.

require a tunnel more than 12 km long with a rock cover of up to 1 200 m, making it impossible to use intermediate shafts for either ventilation or access. This meant that such a tunnel could only be driven from its two end portals. For the next 20 years, various tunnel planners studied how such a tunnel could be constructed – and that was also how long it took to develop the necessary technology. A water-powered compressed air unit had been invented, and the aim was to use the compressed air released by the rock drill as a fresh air supply for the workers. It didn’t work very well. Then they tried to convert a steam-powered rock drill into a pneumatic rock drilling unit, but this didn’t work well either. Nonetheless, despite many drawbacks and uncertainties, it was decided to go ahead, and the project was finally started with an estimated construction period of 20 years. The work began with a pilot tunnel of 3.3 x 2.4 m, which was then enlarged by a crew of 200 to its full cross section of 70 m2 some 25 m behind the face. The first few years were dominated by sledgehammer drilling equipment, and progress was, therefore, slow. The performance records differ slightly on this point, but the daily advance was said to be somewhere between 0.25 and 0.6 m per day. The average hole depth was recorded in the region of 0.5 to 0.9 m.

10

In 1863, the first Sommeillers drilling platform was put into operation. This machine weighed 12 tonnes and was equipped with 4–9 pneumatic rock drills, flushing water tanks as well as a selection of spare parts, and it was operated by a crew of 30 to 40 people.With the introduction of this platform, the maximum advance increased to about 3 m per day during 1864, and this later increased to 4 m per day up to the breakthrough year of 1870. The drillers drilled 0.8 to 0.9 m deep holes, 30–40 mm in a diameter, and there were about 80 men at work in the pilot tunnel at any one time. More than 4 000 people were engaged in the construction of the Fréjus tunnel, and it was completed in 13 years (1870) – significantly faster than the original 20-year estimate. Due to the relocation of the portal on the French side, the total length was also increased to 13.7 km. This was clearly the instigator of a great many other tunnel projects in the Alpine region, several of which belong to the same period up until the turn of the century. The image above gives an idea of how the project was carried out. Here we can see the Sommeillers drilling platform in the pilot tunnel and the drill plan, before the tunnel was enlarged. The drill rods were 3.8 cm (1.5 in) in diameter, and three uncharged holes were drilled to form the initial opening.



Figure 2: Drilling on the 13.7 km long Fréjus Rail Tunnel project started in August 1857 in the Piedmont region of Italy, in the Alps. Above, an old locomotive exits the first tunnel of Fréjus near the town of Modane, on the French side.

However, it wasn’t possible to drill very far before the drill rods had to be sharpened. Reports on bit wear using jackhammers at a contemporary (1865) tunneling site in Massachusetts, USA, make interesting reading. With a tunnel length of 190 m and a cross section of 80 m 2, the drilling of some 10 000 m through mica schist and granite blunted about 150 000 chisels. This meant that the bits had to be reground after every 7 cm. There is no reason to believe that in the same type of rocks a significantly better result had been achieved at the Fréjus tunnel. As for the rock drills, these required constant repairing, and in order to keep 20 machines up and running simultaneously at the face, no less than 60 units were in the workshop at any one time undergoing repairs.

From its setup position, this rig could cover the entire face and enable the drillers to drive the tunnel in one full section operation. As tunneling advanced, the rig was moved forward and repositioned by a truck. A so-called double-front operation was employed whereby drilling and charging was carried out in one tunnel while mucking out was carried out in the other. The hole depth was just over 3 m, and with each blast, the tunnel advanced 2.7 m per round. The drilling was done by six rock drills, known as drifters. An electric excavator with a bucket capacity of 0.4 m3 was used for loading, and productivity was a good 9 m3 per hour. The average advance over a four-week period was 65 m counting both fronts, or one blast per day. 1947 to 1967 was certainly a dynamic period for drilling technology, largely due to the advent of three more technical developments: cemented carbide bits, the lightweight rock drill and the compressed air pusher leg.


11

Tunneling overview

It was during this period that pneumatic drills had their biggest breakthrough, and even though cemented carbide was not available at this time, the drill steel performed significantly better during the construction of the Fréjus tunnel than in the Massachusetts project in the 1860s. This was mainly due to less wearing rock formations. Some 50 years later, at the beginning of the 20 th century, regrinding of drill bits was normally required after 50–60 cm of drilling in gneisses and granites. Fast forward another 30 years (before the introduction of tungsten carbide

bits). It is worth taking a brief look at a case study carried out between 1937 and 1939 that focuses on the construction of a streetcar tunnel in the Hammarby district outside Stockholm, Sweden. The tunnel cross section was 33.5 m 2 and comprised of two separate drives, each 400 m long. The rock was granite, the tunnels were driven from an open area between the tunnels and this This was the first time in Sweden that a so-called drill jumbo was used.


"The Swedish Method" had its international breakthrough in 1946 and was based on light, one-man operated rock drills equipped with pusher leg feeds.

All three did not come along at the same time, but in 1947 they were firmly established, even though it would take several years before they would be fully introduced. Tungsten carbide, which had been discovered some years earlier, was found to be highly resistant to the abrasiveness of rockbearing minerals. Scientists had also succeeded in attaching carbide inserts to the ends of steel rods by means of a special soldering process to form the cutting edges of a drill bit. A lightweight, air-powered rock drill that could be operated by one man represented another huge step forward. As indicated earlier, there were a number of similar models already in existence, but it was the smoothness of the latest models that made them truly superior. In addition, the latest pusher leg, which was also powered by compressed air, was an improvement compared to previous designs. It had a straight feed that pushed the rock drill and bit against the rock. The leg was supported from the tunnel invert. Together, these units were marketed under the name “The Light Swedish Method”. Also better drilling platforms, or jumbos as they were known, were developed that made it easier to move the handheld drills around to cover the large tunnel face areas.

12

One example of how this development impacted subsequent tunneling projects is the Vinstra hydropower plant in Norway, where drilling and blasting was carried out around 1950 when the hydropower plant was expanded. The main headrace tunnel was to be a full 23 km long and had a cross section of 30 m 2, and it took the shape of a D. The project was successful and brought The Light Swedish Method its first international recognition for effectiveness and efficiency. As shown in Figure 2, the tunnel excavation began with a 13 m 2 pilot drive at the invert level with the full tunnel width. The top was then drilled in two steps. During the first shift, the pilot hole was drilled to a depth of about 2 m (7 ft), and the lower crown part, which consisted of five holes, was drilled to twice that depth, followed by blasting and mucking out. During the second shift, the pilot tunnel was drilled again, as were the remaining holes in the crown (the upper part), to twice the pilot hole depth. The crews included six men in one shift, five drillers plus a foreman, and they achieved an average advance of 25 m per week, corresponding to two rounds per day. The mobilization time for each blast was extremely short, reportedly about seven minutes, and the drill bits lasted for 15 m before regrinding was necessary. Ordinarily, the



rock formation at this site, which was reported as mica schist, would have been medium-hard to drill and quite difficult to blast. It was also considered remarkable that during the drilling operations the rock drill was in operation for 85% of the time. This project was later used by Atlas Diesel for marketing the Light Swedish Method. The illustration in Figure 3 shows a drill jumbo for a largesize tunnel that uses a so-called V-cut. In this case, a drill jumbo equipped with 16 feeds of so-called ladder type required eight drillers to keep all 16 fully occupied. All these different types of drill jumbos were the predecessors of what we today mean by drill rigs: a carrier with individually operated booms, each carrying a rock drill mounted on a feed. In the late 1960s, a new period in tunneling techniques developed with the arrival of heavy duty rock drills that could be mounted on drill rigs. This technology came from Ingersol Rand and Gardner Denver in the United States. This forced the Light Swedish Method into the background, although it remained in use for many years for small-size tunneling and, in fact, is still in use in many parts of the world today.

Figure 2: A blueprint of the drilling platform used to create the 30 m2 crosssection tunnel.

A drastic change of technology was soon about to take place – the introduction of the hydraulic rock drill. This invention was launched in the early 1970s and quickly won popularity among its users. These new machines gave about 25% better penetration when compared to air-driven drills at the same impact-power per blow. They could also be designed in such a way that the shock wave that was transmitted to the drill rod transferred significantly less mechanical stress to the drill steel, consequently reducing drill steel consumption. The development of drill steel technology also took a major step forward during this period with the introduction of button bits, which were a crossover from oil drilling technology using roller cone bits. The introduction of the button bit resulted in increased penetration rates of about 20%. These bits were also cheaper to produce, which helped to reduce the cost-per-meter drilled. So what effect did all these technical developments have on tunneling technology? The hydropower plant in Skibotn in northern Norway is a typical case study. The plant was built in the late 1970s and included 35 km of tunnels ranging in size from 18 m 2 to 30 m 2. They were constructed according to contractor Höyer Ellefsen’s tunneling concept, which was based on the use of rubber wheel-bound equipment and loading bays installed every 120 m along the alignment.

Figure 3: A "jumbo" drill rig equipped with hydraulic feed was used for the construction of the Inverawe hydroelectric power station in Scotland, commissioned in 1963.


13

Tunneling overview

To do the job, the contractor used: • Atlas Copco’s drill rig Promec TH 470 with COP 1038 HD rock drills • A truck mounted ANFO charging unit • Caterpillar 980 loaders • Haulage trucks of 10–12 m3 capacity


Known as the "Fréjus Jumbo", this Promec drilling rig was developed specifically for the Fréjus Road Tunnel that runs through the Alps and connects Bardonecchia in Italy with Modane in France. It was opened in 1979.

In terms of manpower, only three men were required – two for drilling and charging and one to operate the loader, and a local firm was subcontracted to haul away the muck. The tunnelers worked a three-shift work schedule, which at that time was still acceptable in Norway, amounting to a 120 h workweek. During a two-month period in the autumn of 1977, an average of 130 m per week was achieved at two fronts. It is possible that this short period is not representative of the entire project, but it still shows what could be achieved with the equipment that was available at the time, namely 10 rounds per day, or 3.3 rounds per shift. A similar example from the same period is the Fréjus road tunnel, which runs close to the old Fréjus railway tunnel described earlier. The total tunnel length was 13 km, and it was driven from the end portals, with one in France and one in Italy. The cross section was 85 m 2. On the French side, regular drill rigs were used including two five-boom rigs and two three-boom bolting rigs. On the Italian side, however, a rig specially built for this purpose was used (see photo above).

14

It was equipped with six booms and used for both blasthole drilling and bolting. Each round consisted of approximately 120 drill holes with a diameter of 51 mm. The depth of the rounds ranged between 4.3 m and 5 m. Mucking out was done with a 150 kW Bröyt digger. Drilling, charging, blasting and scaling took 4.5 h. Mucking, bolting and other reinforcement work took 6.5 h. The average rate of advance was 7.5 m per day with a maximum of 12 m/day. The last years of the 1900s saw the arrival of what came to be known as “computerized drill rigs.” These are also known as CAN-bus rigs because they are equipped with a control system that is completely digitalized. The word CAN stands for Controlled Area Network and means that all commands are transmitted with a digital code via a cable loop to which a variety of functions are connected. For example, when a command is transmitted from a centrally located computer on the rig to a hydraulic valve, the command includes an address



and a task. So how do these technical achievements described above affect the tunneling performance? Looking back over more than 100 years, we can conclude that a driller today can achieve 100 times more than a driller who worked on the first tunnel at Fréjus. It is also somewhat surprising to note that the first Fréjus tunnel was completed in 13 years while the second tunnel took five years to complete. This means that in 100 years, the speed of tunneling has only increased by 2.5 times. When comparing this to developments in other areas of technology, we can conclude that we travel at least 5–10 times faster on rails these days than we did a hundred years ago. Does this mean that technological developments in drilling technology have contributed so little to the end result? The answer is “no” for although today’s construction projects take 50% to 25% of the time they did 100 years ago, the size of today’s workforces is considerably less. On the first Fréjus tunnel, more than 4 000 people were required to get the job done, while the second Fréjus tunnel needed a workforce of less than 400. As a consequence of technical developments, the working environment and safety aspects have drastically improved.

Development of rock support

Rock support goes hand in hand with rock excavation. The development of the technique and the materials used have had a large impact on the growing trend to locate different facilities underground rather than on the surface. Effective ground support has made it possible to build economically even in poor ground conditions. Going back some 200 years or more to the few, short tunnels that were constructed, we can see that the ground was mainly self-supporting, meaning that there was no need for rock support. This meant that tunnel profiles sometimes deviated from their intended shape. The use of brick lining as a permanent support arrived in the early to mid-1800s when tunnel excavation was for civil purposes instead of just being temporary accesses to mines. The linings consisted of ordinary bricks with filling material behind the brick arch, creating contact between the rock wall and roof and the load bearing arch. This type of rock support was installed close to the face or after the excavation had been completed, in which case temporary support was needed to stabilize the ground as the excavation proceeded. Up to the early, mid-1900s, this was standard practice in many parts of the world when tunneling took place in unstable conditions. Judging from the thickness of the lining and the invert strutting, it is obvious that heavy pressure from overlying rock was expected.

crete-based lining soon became the norm in tunnel construction. Concrete spraying and bolting were known methods in the early 20th century but not extensively used. The dry mix type of sprayed concrete became more widely used in the 1950s. The nozzle action was entirely manual, and the operator held it with both hands. Already in the early 1960s, rigs for maneuvering the nozzle were introduced, and with that the old brick linings for permanent support became completely obsolete. When tunneling in strong crystalline basement rock, insitu concrete linings were only rarely used. In those cases, sprayed concrete was used both as primary and secondary linings. The sprayed concrete was mostly applied in connection with the installation of rock bolts. Bolts had been used in mining and were now well accepted in the civil construction industry, both the pre-stressed type as well as the dowel type. Knowledge of the interaction between the support and the rock itself came with the works of Therzagi in the 1930s, during which the timing factor for the installation of support was introduced. The science of rock mechanics was introduced after the Second World War by a group of researchers in Salzburg, Austria, in which Leopold Müller played a major role. This group started the geo-mechanic colloquium, a seminar on rock mechanical issues in relation to surface and underground construction. They held their annual meetings in Salzburg, and these meetings are still held there today. It was in this environment that the well-known “New Austrian Tunneling Method” NATM was created. It is easy to understand that this approach to tunnel excavation and rock support was embraced by many when studying the concept of the traditional Austrian tunneling method. However, it


15

Tunneling overview

Up to the mid or early 1900s, temporary support elements were mainly constructed in wood. In the 1930s, steel was being used extensively as primary support because steel arches became available at an acceptable cost. A final con-

The Atlas Copco Boomer was introduced in the 1970s and became a standard rig for tunneling and drifting, marking the entry of hydraulic drilling equipment.


must be said that this technique has been misinterpreted by many tunnel builders who believe that they are applying this technology as soon as they use sprayed concrete support. The whole concept of “ground reaction” in relation to tunnel excavation and support has paved the way for tunneling in poor ground conditions, especially when there is large overburden. Up until the present day, NATM technology is frequently applied in tunnel support, although there is a tendency to avoid intense splitting of the tunnel face and to carry out the excavation in stages. This is one way to control the deformation. The splitting work is time-consuming, and an alternative to improve the stability of the ground ahead of the face, and thus reduce or eliminate the splitting, has become more widely used. Consequently, pipe roofing and spiling currently play a major role in poor ground excavations. Support of the tunnel face itself by bolts in the form of long fiber strands are only applied where major deformations of the face are foreseen. Secondary linings today consist of either concrete or sprayed concrete. The choice depends on the geology but is also influenced to a large extent by the conventional design of having a final lining that is capable of handling the entire rock load, not including the primary support as a part of the final lining. In Scandinavia, which has mainly competent crystalline basement rock, sprayed concrete lining is the dominant method, but in similar rock conditions in Hong Kong and, to a large extent, in India, concrete lining is the preferred method. In regions dominated by sedimentary rock, concrete lining is by far the preferred method, even when tunnels are excavated in igneous rock. Segmental lining as a single shell method of support is commonly used in connection with TBM (Tunnel Boring Machines) tunnel excavations. It was introduced in the 1960s but became widespread in the 1970s, particularly in soft ground tunneling. The Japanese developed the slurry technology that suited the fast growing city of Tokyo, which is founded on thick layers of mainly friction soils. The advent of TBM tunneling meant that the extensive cut-and-cover tunneling used at that time could be abandoned, much to the relief of the citizens.

Mechanical excavation

Tunneling by use of mechanical excavation instead of by means of blasting agents started in the 1950s, albeit on a very small scale. It was the mining engineer James Robbins who built the first TBMs where the so-called disccutter was the cutting tool. More than 100 years earlier, TBM excavations had been made under the river Thames in London, but during that project only ripping teeth were used to cut through the London clay. The first generation of TBMs had relatively small disc cutters capable of

16

dealing with loads of about 8 tonnes, while the TBMs of today can handle loads of up to 35 tonnes. Certainly the cutters have grown in size and so has the rock surface on which the cutter is pressing. The net result is that the penetration of the cutters has drastically improved, especially in very high strength rock formations (300 MPa) where the TBMs with small cutters had penetration in the range of fractions of a millimeter, while today, in similar conditions, they are in the range of 4 mm per cutter-path or full 360 degree rotation of the cutter-wheel. However, most TBM tunneling is made in sedimentary rock, which is not surprising considering 70% of the Earth’s land mass is covered with sedimentary rock. The lower strength of the sedimentary rock material allows for good penetration, and consequently many tunnel meters can be achieved per day. Over the years, the TBMs have become more powerful as cutters have become more capable of taking on even larger loads. This means that the TBM technique is doing more of the tunneling that was previously done by the drill and blast method. The TBM technique has also increased the amount of tunnel meters being driven worldwide as decision-makers have become increasingly aware that this solution is economically viable for many new applications, such as tunnels instead of bridges and trenches. As a result it is clear that the total number of tunnel meters created by drill and blast has most likely not been reduced by the introduction of the TBM. Over the past 15 years, cutting technology has not been developed very much, aside from an increase in cutter sizes and applied cutting power. However, transporting the broken rock (muck) via conveyors has become very common. Conveyor mucking offers a continuous process with a high capacity. The soft ground TBM technique has certainly been embraced by city planners and decision-makers when it comes to tunneling for subway systems. The capability of dealing with a great variety of soil conditions at moderate depth is a big success story. A large number of TBMs are presently at work upgrading the transportation systems for some major Chinese cities. Roadheader excavation of tunnels entered the construction market in the 1960s. This machine has its origin in the mining industry, primarily in coal mining. They became fairly popular in the 1970s and 1980s when they were used to excavate tunnels in sedimentary rocks and soft materials. But as the TBMs became more competitive in this type of ground, even for shorter tunnels, the demand for roadheaders diminished. The drawback of roadheader technology is its strong dependence on the strength of the excavated rock material. For small tunnels, this was more obvious as the smaller machines are very limited in terms of rock strength, and all machines, whatever their size, have problems if the rock is very hard and abrasive. Today, there is very little left of roadheader tunneling in civil construction. ◙



17

Tunneling overview

Workers from the French and Italian side of the Alps meet at the middle of the Mont Blanc Tunnel, completed in 1965.

Global outlook: Continued population growth and urban expansion around the world will require new tunneling projects and upgrades to existing infrastructures.

The essential role of tunnels: a look into the future

Creating a functioning yet sustainable society is one of the great issues of the 21st century. Fortunately, man’s ability to construct tunnels goes a long way to solving an array of challenges in the most efficient way, from transportation to water supply. The tunneling industry is entering its most rapidly evolving and, arguably, most exciting era. Whether in good economic times or bad, tunnels are an essential component of functioning societies all around the world. They are indispensable for public transport, roads and rail networks, for supplying fresh water to cities, building sewage systems, constructing hydropower stations that generate renewable energy, and providing facilities for storage, communications and a range of other applications. In the future, underground construction will undoubtedly increase to meet the growth of urban populations and the

18

continued expansion of infrastructure in and between cities. Furthermore, existing tunnels must also be upgraded so that modern standards for safety and efficiency are upheld and guaranteed for the 21st century. So, what are the most important trends from a global perspective? They can be revealed by studying the key factors that characterize the tunneling industry of today: volume of rock, excavation methods used, safety aspects, costs, the availability of labor, type of underground openings, and geology.


THE ROLE OF TUNNELS: GLOBAL MARKET OVERVIEW

Tunnel Construction output by geographical areas Europe North America Japan China India South America Others 0

20 000

40 000

60 000

80 000

100 000

Figure 1: Annual construction costs in million USD. (Source: ITA-AITES, International Tunnelling and Underground Space Association).

The global picture: excavation volumes

In contrast to the mining industry where volumes are measured in tonnes, excavation volumes in tunnel construction are exclusively described using solid cubic meters (m3) as a reference. A typical exception to this rule is the haulage capacity of conveyor belts and trucks where the concept of tonnes may also be used in addition to cubic meters (m3). Although annual excavation volumes from underground construction grow over time, they are not constant and fluctuate. The reason is that tunneling projects are very large and complex undertakings, fraught with challenges that need to be overcome, and this may affect growth statistics. While it is very difficult to provide exact figures, the generally accepted view is that the total annual volume from underground excavations in rock is somewhere in the range of 100 million m3. According estimations by ITA-AITES (International Tunnelling and Underground Space Association), the total volume including soft material will be almost double.

As the combined populations of India and China have already surpassed 2.5 billion, it is more than reasonable to assume that many new subway lines will be needed to meet the demand for increased public transportation capacity as more and more people choose to relocate to cities. It has also been estimated by ITA that the value of the annual global underground construction is in the region of USD 90 billion which corresponds to roughly 5 000 km of tunnels. How this dollar value estimation is divided across the world’s regions is illustrated in Figure 1.

Growth in Asia

China is currently the nation with the largest underground construction schemes, where some 40 million m 3 of rock


19

Tunneling overview

The figure, which is only a fraction of annual volumes in mining, can be visualized and more easily referenced by imagining a cube of rock that has a side length of 470 m. An easier way, perhaps, of relating to this figure is to convert it into kilometers of subway tunnel. In a typical scenario where

a single-track tunnel has a cross section of 30 m2 with added volumes for stations at every 1 to 1.5 km, the figure 100 million m3 will correspond to 3 000 km of single-track subway. For the sake of useful comparison, one might consider the city of Stockholm, the Swedish capital, as an example as it has roughly 1 million inhabitants and a 100 km long doubletrack subway system. The global annual figure for excavation volumes in tunneling would be the equivalent of developing new subway systems in 15 Stockholm-sized cities.


km

Total length of metro lines in operation in China

1 700

1 699

1 600

1 471

1 400 1 200 999

1 000 763

800 600

835

621

400 200 0 2006

2007

2008

2009

2010

2011

Figure 2: Increase of subway line construction in China in kilometers over recent years. (Source ITA-AITES, International Tunnelling and Underground Space Association).

are excavated. This corresponds to 40% of the world’s total underground construction operations in rock. In this approximate figure, 500 km of road and railway tunnels will most likely represent 30 million m3. The rest is comprised of excavations for hydropower facilities and a program for storing hydrocarbons in unlined rock caverns. To be able to maintain its policy of storing three months of the national consumption of oil, China will require a storage capacity of 60 million m3. The current designated program stipulates that construction over a 10-year period will result in 6 million m3 annually of excavated volume. A large share of the oil reserves will, however, be stored in steel tanks.

where there is significant potential for hydropower. These projects in Bhutan are often financed by Indian capital, and most of the designs require long and large tunnels with underground power stations, meaning that the excavation volumes will be large. Major cities in India, such as New Delhi, Kolkata (Calcutta), Bangalore and many others, are already building new railway transport systems. A large proportion of these are being developed underground.

The annual figure for underground excavation in soft material exceeds the rock excavation volume. More than half of the worldwide underground volumes (estimated at about 200 million m3) is excavated in China. An example of this growth is demonstrated in Figure 2, showing where subway lines have been extended by more than 1000 km over a five-year period.

Just like its neighboring country China, India also has a program for storing hydrocarbons in unlined rock caverns. Although the program is a lot smaller, it still contributes millions of excavated cubic meters. Indochina (Myanmar, Cambodia, Laos, Singapore, Thailand and Vietnam) also has a strong potential for hydropower, particularly in Vietnam and Laos. Here, construction is moving forward continuously as more and more end-customers in Vietnam and Thailand are prepared to accept the price of electric energy.

The remaining regions of Asia represent some 25% of the global underground excavation volumes. Here we see hydropower construction increasing its volumes, not just along the rivers that dewater the Himalayas in India, but also in Bhutan

Moving on to Japan, which comes second place after China in terms of excavated volumes despite declining figures in recent years, road tunnels make up the largest share of underground construction volume followed by railway tunnels.

20



European outlook

Europe is the third largest market for underground construction with an annual volume that amounts to 13 million m3 of rock, which corresponds to 15% of worldwide volumes. Among the projects, road and railway tunnels are the dominating structures. Hydropower accounts for a small share of the total volume as most locations that are suitable for hydropower generation have already been developed, and power stations have been installed. Nonetheless, there is a continued market for hydropower construction in Europe because many facilities will need to be modernized in the years ahead. Very few hydropower stations are older than 100 years, yet numerous facilities are in dire need of upgrading basic structures, such as tunnels, waterways and caverns. Pump storage schemes are necessary supplements to electricity generated from wind power, which is also likely to see growing interest in the coming decades. At the same time, excavated volumes of rock and soil for these structures are quite small by comparison and have a negligible impact as far as statistics are concerned. Major tunnel projects are in the planning stages, including rail and subway projects, that will contribute large volumes of excavated material to these statistics. Out of the total world output of USD 90 billion annually, Europe represents more than 10% and will, most likely, continue to do so. An Atlas Copco Boomer E2 C drill rig is hoisted via cable car installations to the Project Linthal 2015, a hydropower construction site in the Swiss Alps.

Modernization in the North America

Underground construction in the U.S. is mainly focused on tunnels for roads and subway lines, although a considerable share also deals with stormwater storages and sewage systems. The excavated volumes of rock are just over half of those recorded in Europe, and the numbers for soft ground excavation are far lower than the European ones. As is true in Europe, where infrastructure roughly meets current demand, much of the tunneling being done involves the upgrade and replacement of old underground structures. These are designed to meet the gradually increasing demand for capacity as the populations of the larger cities increase. The major underground works taking place in New York City to expand and upgrade the public transport system are a good example (see case article on p. 242).

South America on the rise

In South America, some nations are still in the development phase, and there is a growing need for both infrastructure and power. Furthermore, the continent has great potential for generating hydropower that may be beneficial in meeting the increased demand for energy.

Other regions

For Africa and Australia, the underground volumes in construction are small when compared to the other continents, and they are estimated to be below or in the range of 1% of the total figure. Having said this, a number of countries in Africa are developing rapidly, and the demand for energy is undoubtedly destined to increase immensely. With many suitable locations for renewable hydropower, particularly in central parts of the continent, tunnels will also be required. It remains to be seen to what extent these facilities will involve underground structures.

Excavation methods

From the perspective of giving a global insight into the tunneling industry and where it is headed, the type of excavation methods used is another important aspect. There are currently three methods that dominate practices worldwide – drill and


21

Tunneling overview

In the Andes mountain range, many tunneling projects will be required if roads and railways are to be built according to modern standards for high speed. Underground construction

in rock corresponds to roughly half of the European volumes, about 6 million m3 per year. Large railway projects are underway in Brazil, indicating that excavation volumes will increase in the near future.


Excavation methods

100% 90% 80% 70% 60% 50% 40% 30% 20%

Other methods

10%

TBM Drill and Blast

0% Austria

India

USA

Chile

Japan

Figure 3: Tunneling is dominated by two main excavation methods; TBM (Tunnel Boring Machine) and drill and blast. The choice is largely dictated by geology and the tunnel design. Soft rock (TBM) is more prevalent in North America while hard rock conditions characterize European tunneling (drill and blast).

blast excavation, mechanical excavation by use of Tunnel Boring Machines (TBMs) and mechanical excavation using road headers. As shown in Figure 3, the distribution of excavation methods in rock, hard to loose, varies greatly between different regions, but also over time as technologies develop. A large share of TBM excavations are carried out in soft ground conditions, and this is also the most common method for developing subway tunnels in large cities. It is also used to some extent for road and rail tunnels. Many of today’s metropolitan areas were founded as cities centuries back when shipping was the principal method for transporting goods. This means that large cities are often located along river estuaries because they conveniently linked the sea with the inland, thereby linking consumers and traders with producers. What is more, river outlets are generally considered major settlement areas for sediments brought in by the rivers. Typical examples of this are Shanghai, Tokyo, and Amsterdam. By contrast, cities such as Hong Kong, Stockholm, and Sydney have opposite conditions where most buildings are founded on solid rock or have a short underpinning down to the solid rock.

22

As a consequence of the above, it is estimated that about two-thirds of all TBM excavation work is carried out in soft ground conditions. A typical nation that favors TBM is the U.S. where more than 90% of tunnels are driven by TBM. A typical non-TBM nation is Finland, which to this date has not had a single TBM project as all excavations have been performed by drill and blast. Japan is a nation where rock excavation projects tend to favor drill and blast. A reason for this is that a major share of the market consists of large tunnels of moderate lengths for road networks, conditions for which this method is wellsuited. There are a number of aspects influencing this large discrepancy between countries and the types of excavation methods used. Geology is one important factor. It is well-known that high strength rock (UCS 200 MPa) does not favor the use of mechanical excavation. While practically possible, it is, in most cases, simply not economically viable. By contrast, sedimentary rock with a low quartz content does favor mechanical excavation, as tunneling in soil using the drill and blast method is less than ideal.



Recruiting skilled professionals

The availability of skilled staff is a crucial issue for the tunneling industry as a whole. One reason for this is that fewer and fewer personnel have enough experience with conventional excavation methods. The drill and blast method offers a certain flexibility when facing varying ground conditions that is not possible to achieve with TBM equipment. But there are other reasons, too. Flexibility is key for today’s contractors, and that puts greater demands on finding personnel who are willing to travel and work in different countries, often in strenuous conditions. In the U.S., a result of this development is that drill and blast is now only employed to a marginal degree as it has proven to be easier to train people for operating and handling a TBM excavation. Although geology and the availability of personnel have proven decisive in terms of tunneling methods, there are other important factors that have more to do with tradition and the type of tunnels that are in demand. A good example of this is Japan, which has many drill and blast projects despite the fact that the country is largely characterized by soft ground conditions. Japan has developed a large number of road tunnels with large cross sections in areas that are not dominated by soft ground. In the 1980s, the situation was very different because projects tended to be located in the typical soft ground areas. Austria is another country where drill and blast excavation has traditionally been the method of choice. However, Austrian contractors are now increasingly embracing mechanical excavation methods as their Swiss neighbors have been doing for the past few decades.

Safety comes first

In addition to the above, the choice of tunneling method is, to a large extent, dictated by economic factors. Achieving the lowest possible costs for a project is always a strong incentive for choosing one method over another, but safety and risk assessments must always come first. The hydropower facilities that are being excavated in the Himalayan mountains in India, where rock mechanical conditions are highly challenging, are a good example of how estimated risks have been decisive in choosing between a drill and blast or TBM excavation process. In this case, a number of TBM projects did not turn out as expected which has brought about a more realistic view on which conditions the excavation methods can handle.

In addition to the risk factors associated with tunneling projects, speed of excavation and costs are key factors to consider,

and they will always vary depending on the location of the project, the availability of skilled labor, salaries, regulations, and more. Comparing the excavation rate between one method and another is relatively easy to do when ground conditions are known beforehand. This is, unfortunately, not the case for the vast majority of tunneling projects, which means that completion dates and costs are usually quite difficult to establish. This fact becomes obvious when comparing the accuracy of estimations for structures such as houses and bridges where almost all work is carried using well-defined materials. At the Lötschberg tunnel in Switzerland, one of two Alp transit tunnels excavated in the most recent decade, a section of the excavation offered the opportunity to make a comparison in practice. Over a parallel tunnel excavation, one tunnel was excavated by TBM and the other by drill and blast. As the result shows in Figure 4 (next page), the average advance rate for the drill and blast method is roughly half that of the TBM method, although there are deviations depending on which tunnel is considered. A cost comparison has also been made. Here, it can be concluded that the TBM excavation has been completed at a lower cost in poorer ground conditions and vice versa in better ground conditions, in reference to rock stability.


23

Tunneling overview

Cost and excavation rate

Finland is a typical non-TBM nation . All tunnel excavations to date have been performed with the drill and blast method.


35

meters/day

Advance rates at the Lötschberg tunnel in Switzerland

30 25 20 15

TBM maximum

10

TBM average

5

D&B maximum

0

D&B average PA 11

PA 12

PA 14

PA 15

PA 16

PA 18

Figure 4: Average and maximum advance rates for the tunnel reach during the Lötschberg Base Tunnel excavation, Switzerland.

This is not unusual as long as the ground conditions are moderately poor. In very poor ground, there are numerous cases where a TBM has got stuck, and the excavation has been abandoned in favor of drill and blast excavation. This means that a successful TBM excavation is heavily dependent on pre-investigations regarding the geology along the tunnel route, which, therefore, are normally more extensive. It is a prerequisite that all parties involved can contribute to ensuring that the time schedule and costs are as accurate as possible.

Innovation leads the way

As cities expand around the world to cater to growing populations, tunnel designs are getting more complex. A common effort to meet this challenge is perhaps the biggest industry trend at the present time. It goes hand-in-hand with safety, the need for expertise, ground conditions and costs. Innovation is driving the industry forward, and new technologies are

24

becoming increasingly available. The use of sprayed concrete to stabilize tunnels as they are driven has revolutionized the tunneling industry in just a few years. The use of 3D technologies and advanced data management software are also becoming widespread. These technologies have also paved the way for far greater precision in the excavation process, which governs both time and costs. But that’s not all. The conditions for financing tunneling projects are also changing rapidly, and the importance of environmental concerns will only grow in the years ahead. In fact, there are many indications that the demand for tunnels will increase significantly as the lack of space and environmentally acceptable solutions on the surface of the planet become more evident. All of these issues and more will be looked at more closely in the following chapters of this technical reference book for tunneling practices. ◙


25

Tunneling overview


1 2 3 4

1000

2000

3000

4000

5000

(km)

6000

1 Earth Crust 2 Mantle 3 Outer Core 4 Inner Core

Figure 1: The Earth’s interior consists of four main layers. Heavy metals such as iron and nickel are most abundant in the core. 1 2 3 4

Earth Crust Mantle Outer Core Inner Core

Tackling the challenges of sub-surface space A deep understanding of geology and of the nature and characteristics of the rock and soil at a proposed tunnel site, are prerequisites for successful tunnel excavations. Selecting the method, choosing equipment, designing a rock support system and a dozen other key decisions that will affect the success of a tunnel construction project, are all directly related to geology and rock characteristics in and around a proposed tunnel site. Conversely, without a thorough knowledge of the geological facts, these decisions could have potentially disastrous consequences. Although geologists have not probed the planet to its core, they are confident in their grasp of what the Earth looks like beneath its crust, and of the properties of the various rock

26

types that have been formed over millions of years. What is important to the tunneling engineer, however, is how this expertise impacts on the practical realities of tunnel construction.

How the Earth was made

The Earth consists of an inner and an outer core surrounded by a mantle. At the surface is a thin layer of rocks known as the crust, shown in Figure 1. This shell-like structure has been confirmed by studying seismic waves originating from


GEOLOGY AND WHY IT MATTERS

Samples of common rock types: Amphibolite, Diabase, Dolomitic limestone, Gneiss, Granite, Sandstone.

earthquakes. The velocity, or propagation, of these waves is related to the density of the material and its state, be it solid or liquid. According to this interpretation, the inner core is solid and the outer core is liquid. The mantle and the thin crust of the Earth are solid, apart from the shallow layer of the mantle, also known as the “upper mantle”, which is composed of plastic flowing rock about 200 km thick. The motion of this layer forms the basis of plate tectonics. The thickness of the core and mantle each correspond to roughly half of Earth’s radius and we can observe only the upper part of the Earth’s crust. The deepest drill hole is 11 km, but we can get information from the equivalent of tens of kilometers by studying eroded mountain chains. Earth was formed more than 4.6 billion years ago by aggregation of cosmic material from our solar system. The meteorites falling down on Earth are of the same origin as our planet so, by studying this material, we can get data about the chemical composition of the deeper sections of the core.

However, there is a great difference in thickness between oceanic crust and continental crust. Under a mountain chain the crust thickness can be up to 70 km. The chemical composition of the outer part of the crust is well known, and is dominated by eight elements: oxygen, silicon, aluminum, iron, magnesium, calcium, sodium and potassium. The continental crust is higher in silica, aluminum and alkali due to the high content of granitic rocks. The oceanic crust is lower in silica but higher in magnesium and iron due to the dominance of volcanic rocks, mainly basalts. Of the 155 known elements, some of which do not occur naturally, oxygen is by far the most common, making up about 50% of the Earth’s crust by weight. Silicon forms about 25%, while aluminum, iron, calcium, sodium, potassium, magnesium, titanium, silicone, oxygen and other common elements build up the total to 99% of the Earth’s crust. Silicon, aluminum and oxygen occur in the most common minerals


27

Rock classification

There are two types of meteorites: stone meteorites dominated by Fe-Mg-silicates, or chondrites; and iron meteorites mainly consisting of metallic iron and nickel. Seismic and meteorite data indicate that the chemical composition of the core is

similar to iron meteorites and that of the mantle is similar to stone meteorites. The difference in density also explains the velocity of seismic waves in the core and mantle, and the high average density of the earth, which is about 5.5 g/cm3. The thickness of the crust is normally between 10 and 35 km.


1

9

2

10

11

3

12 13

4 5

14

6

15

7 8

1 North American plate 2 Juan de Fuca plate 3 Caribbean plate 4 Cocos plate 5 South Amercian plate

6 Nazca plate 7 Scotia plate 8 Antarctic plate 9 Eurasian plate 10 Pacific plate

11 Arabian plate 12 Indian plate 13 Philippine sea plate 14 African plate 15 Australian plate

Figure 2: The tectonic plates were mapped in the second half of the 20 th century. They consist of the Earth's crust and uppermost mantle, together referred to as the lithosphere.

such as quartz, feldspar and mica, which form part of a large group known as silicates, being compounds of silicon and other elements. Amphiboles and pyroxenes contain aluminum, potassium and iron. Some of the planet’s most common rocks, granite and gneiss, are composed of silicates. Oxygen also occurs commonly in combination with metallic elements which are often important sources for mining purposes.

which includes the whole of South America and a part of the Atlantic, and the African plate consisting of the African continent and parts of the Atlantic and Indian Oceans.

Plates can interact by moving apart (divergence) or towards each other (convergence). When two continental plates collide, mountain ranges may be formed (see Figure 3). Thus the collision of the Indo-Australian and Eurasian plates resulted in the formation of the Himalayas, the highest mountain chain 1 North American plate 9 Eurasian plate Tectonic plates on earth. When an oceanic plate moves towards a continental 2 Juan de Fuca plate 10 Pacific plate The modern3theory of plate tectonics has improved our underplate such as South America, the oceanic plate will move Caribbean plate 11 Arabian plate standing of 4basic geological processes like formation of rock Cocos plate 12 Indian platebelow the continent, or subduct. When the oceanic plate starts volcanism, 5earthquakes and theplate formation of many of sea to melt, South Amercian 13types Philippine plate volcanic activity will occur. Therefore, we find a 6 Nazca plate 14 African plate ores. great number of volcanoes along the western part of South 7 Scotia plate 15 Australian plate America, to mention one example. Subduction also leads to plate According 8to Antarctic this theory, the crust and upper part of the the formation of ores. mantle can be divided into 10 to 12 major plates, which move in a complex pattern (see Figure 2). The driving force of this In the middle of the Atlantic there is a long chain of volcamovement can be attributed to heat generated by radioactive noes called the mid-Atlantic ridge. Similar ridges are found decay within the mantle and core. The heat is transported by in the other oceans. Along these ridges two oceanic plates slow convection streams, which move the plates and the speed are moving apart as magma rises from the mantle below and of the motion of plates is just a few centimeters per year. solidifies. This causes repeated eruptions of basaltic lava, forming a new ocean floor. The youngest volcanic rocks Three major plates are North American which includes are found close to the ocean ridge, and the age of the rocks North America, Mexico and Greenland, South American increases out from the spreading center. The mechanism of

28



3 2

1

1 Collision zone 2 Oceanic ridge, spreading zone 3 Subduction zone

Figure 3: Tectonic plates interact by moving apart (divergence) or towards each other (convergence). When an oceanic plate moves toward a continental plate, the oceanic plate moves below the continent which creates a subduction zone.

seafloor spreading is an important part of the plate tectonic theory. Volcanic activity occurs above hotspots and in spreading zones. There are three types of volcanoes that are shaped by their tectonic surroundings: rift volcanoes, emerging in spreading zones: stratovolcanoes, which are located along the subduction zones: and shield volcanoes, located above hotspots. Volcanism also occurs due to the collision of plates but is distinguished from earthquakes, as these occur when two plates are sheared or slide along each other, such as in Los Angeles, and not from the movement of magma.

mixed, consisting of both homogenous and heterogeneous structures. In addition, minerals have a wide variety of properties and characteristics, including the following: • Hardness • Density • Color • Streak • Luster • Fracture • Cleavage • Crystal structure

Mineral properties and characteristics

The particle size and the extent to which the mineral is hydrated (mixed with water), indicate the way the rock will behave when excavated. Hardness is commonly graded according to the Mohs 10-point scale, as shown in Table 2. The density of light colored minerals is usually below 3 g/cm3. Exceptions are barite or heavy spar (barium sulphate – BaSO4 – density 4.5 g/cm3), scheelite (calcium tungstate – CaWO4 – density 6.0 g/cm 3) and cerussite (lead carbonate – PbCO4 – density 6.5 g/cm 3). Dark colored minerals with some iron and silicate have densities of between 3 and 4 g/cm 3. Metallic ore minerals have densities over 4 g/cm3, and gold has a very high density


29

Rock classification

A mineral is a natural chemical compound with a defined crystal structure and composition. A rock, on the other hand, is a naturally formed aggregate of minerals. There are thousands of different minerals but only about fifty rock-forming ones, most of which are silicates, always containing silicon and oxygen. Feldspars account for almost 50% of the Earth’s crust and are hence the most common mineral (see Table 1). Feldspars can be grouped in alkali feldspar and plagioclase. The second most common minerals in the crust are pyroxene and amphibole followed by quartz and mica. Together these minerals make up about 90% of the Earth’s crust. It is true to say that mineralization is rarely pure. Instead, it is usually

n tio za lli a t ys

MAGMA

Sm el tin g

Me tam orphis m

RY

g erin p. Weath trans Erosion

PHIC MOR TA S ME ROCK

MA GM RO ATIC CK S

C r


SE

D

IM

TA EN S M K DI OC E R S

EN TS

Cementation

Figure 4: The rock forming cycle shows the creation of various rock types and how they deteriorate.

Rock forming minerals Feldspar

58%

Pyroxene and amphibole

13%

Quartz

11%

Mica

10%

Olivine

3%

Others

5%

Table 1: Feldspar is the most common rock forming mineral.

Hardness grading Moh´s hardness scale

Typical mineral

Identification of hardness

1

Talc

Easily scratched with fingernail

2

Gypsum

Barely scratched with fingernail

3

Calcite

Very easily scratched with a knife

4

Fluorite

Easily scratched with a knife

5

Apatite

Can be scratched with a knife

6

Orthoclase

Difficult to scratch with a knife, but can be scratched with quartz

7

Quartz

Scratches glass and can be scratched with a hardened steel file

8

Topaz

Scratches glass and can be scratched with emery board /paper (carbide)

9

Corundum

Scratches glass. Can be scratched with a diamond

10

Diamond

Scratches glass and can only be marked by itself

Table 2: Hardness is commonly graded according to the Moh's 10-point scale.

30

of 19.3 g/cm 3. Although ore forming mineral density may be high, the total ore density depends entirely on the host rock where these minerals exist. Streak is the color of the mineral powder produced when a mineral is scratched or rubbed against unglazed white porcelain, and may be different from the color of the mineral mass. Fracture is the surface characteristic produced by breaking a piece of the mineral and is usually uneven in one direction or another. Cleavage denotes the properties of a crystal whereby it allows itself to be split along flat surfaces. Both fracture and cleavage can be important to the structure of rocks containing substantial amounts of the minerals concerned. Rock normally comprising a mixture of minerals, not only combine the properties of these minerals but also exhibit properties resulting from the way in which the rocks have been formed, or perhaps subsequently altered by heat, pressure and other forces in the Earth’s crust. The mineral composition of rock is key to our understanding of the behavior of rock and how natural stress fields and fracture properties come into play. Stress fields in the rock arise partly because of the rock mass weight, but also due to movements caused by geological processes. Rock mass is a synonym of bedrock and refers to the rock plus discontinuities in the rock amassed in large volume. These discontinuities are important not only for the structural integrity of a tunnel, but also as paths for fluids in the Earth which cause mineral concentrations.

Appraising the rock

For drilling during tunnel construction, the rock must be correctly appraised as the results will affect projected drill penetration rates, hole quality and drill steel costs. In order to determine overall rock characteristics, it is necessary to distinguish between microscopic and macroscopic properties. As rock is composed of grains of various minerals, the microscopic properties include: • Mineral composition • Grain size • The form and distribution of the grain • If the grains are loose or cemented together Collectively, these factors comprise the properties of the rock, such as hardness, abrasiveness, compressive strength and density. In turn, these rock properties determine the penetration rate that can be achieved when drilling blastholes and the extent of the wear on the drilling equipment. In some circumstances, certain mineral characteristics will directly influence the tunneling method. Many salts, for example, are especially elastic and can absorb the shock from blasting.

Rock drillability

Drillability depends on the hardness and brittleness of the rock’s constituent minerals and on the grain size and crystal habit, if any. For example, quartz, which is one of the



Typical igneous (magmatic) rock types Silica (Si02) content

Intrusive (plutonic rocks)

Hypabyssal (dykes and sills) Extrusive (volcanic)

Ultramafic <45% SiO2

Peridotite

Kimberlite

Komatiite

Mafic 45-52% SiO2

Gabbro

Diabase

Basalt

Diorite

Porphyrite

Andesite

Syenite

Syenite

Trachyte porphyry

Quartz diorite

Quartz porphyrite

Dacite

Intermediate 52-63% SiO2

Felsic >63% SiO2

Granodiorite

Granodiorite porphyry

Rhyodacite

Granite

Pegmatite

Rhyolite

Table 3: Main igneous rock types according to chemical composition (silica content) and location where magma turned into solid rock.

commonest minerals in rock, is a very hard material, exceedingly hard to drill and will certainly cause heavy wear, particularly on drill bits. This is known as abrasion. Conversely, a rock with a high content of calcite can be comparatively easy to drill and cause little wears on drill bits. With regard to crystal habit, minerals with high symmetry, such as cubic galena, are easier to drill than those with low symmetry, such as amphiboles and pyroxenes. In terms of drillability, rocks with essentially the same mineral content may be very different. For example, quartzite can be fine grained (0.5-1.0 mm) or dense (grain size 0.05 mm). A granite may be coarse grained (size >5 mm), medium grained (1-5 mm) or fine grained (0.5-1.0 mm). A rock can also be classified in terms of its structure. If the mineral grains are mixed in a homogeneous mass, the rock is termed massive (isotropic), as with most granite. In mixed rocks, the grains tend to be segregated in layers (anisotropic), whether due to sedimentary formation or metamorphic action from heat and/ or pressure.

Rock formations

There is a relationship between magmatic, sedimentary and metamorphic rocks, as shown in Figure 4. Starting with the magma at the top of the figure and going down to the left, the magma will crystallize into a magmatic rock due to decreasing temperature and pressure. If crystallization occurs within the crust, an intrusive rock results, for example, granite. If the magma is erupted by volcanic activity, the result will be rhyolitic lava, or a tuff of similar composition. All rock formations irrespective how they were formed exposed to surface conditions are being weathered and eroded by both chemical and mechanical processes. Chemical weathering will decompose many minerals, but the remaining part of more resistant minerals and rock fragments will be transported by water, ice or wind until deposition occurs.

However, there are also some other possibilities. When metamorphic rocks are exposed at the earth’s surface, weathering starts and the cycle is short-circuited. Erosion and weathering will transform the rock into sediment, which later can form a sedimentary rock. There is also a possibility that a magmatic rock is metamorphosed without forming a sedimentary rock in between. In other words, recycling of rocks is a constant, ongoing process. It is therefore important to identify the rock’s origins which are divided into three classes: • Igneous or magmatic – formed from solidified lava at or near the surface, or magma underground • Sedimentary – formed by the deposition of reduced mate rial from other rocks and organic remains or by chemical precipitation from salts, or similar • Metamorphic – formed by the transformation of igneous or sedimentary rocks, in most cases by an increase in pressure and heat.

Igneous or magmatic rock

Igneous rocks are formed when magma solidifies, whether plutonic rock, formed deep in the Earth’s crust as it rises to the surface in dykes cutting across other rock or sills following bedding planes, or volcanic, as lava or ash on the surface. The most important mineral constituents are quartz and silicates of various types, but mainly feldspars. Plutonic rocks solidify slowly, and are therefore coarse-grained, whilst volcanic rocks solidify comparatively quickly and become fine-grained, sometimes even forming glass. Depending on where the magma solidifies, the rock is given different names, even if its chemical composition is the same, as shown in the table (see Table 3) of main igneous rock types. A further subdivision of rock types depends on the silica content.


31

Rock classification

After sedimentation, compaction and cementation of the mineral grains, a sedimentary rock is formed. If the sedimentary

rock is buried deeper and deeper under other rocks and sediments, the increasing pressure and temperature will cause re-crystallization, often combined with the formation of new minerals. A metamorphic rock is formed. At great depth in the crust the metamorphic rock will start to melt and form a new magma, and the cycle is completed.


Some sedimetary rock types Rock

Original material

Conglomerate

Gravel, stones and boulders, generally with limestone or quartzitic cement

Greywacke

Variable grain size from clay to gravel, often with angular shape

Sandstone

Sand

Clay

Fine-grained argillaceous material and precipitated aluminates

Limestone

Precipitated calcium carbonate, corals, shellfish

Coals

Vegetation in swamp conditions

Rock salt, potash, gypsum, etc

Chemicals in solution precipitated out by heat

Loess

Wind-blown clay and sand

Table 4: Typical sedimentary rock types and the material from which they originate.

Rock with high silica content is called felsic, and those with lower amounts of silica are called Ultramafic or mafic, also demonstrated in Table 3.

Sedimentary rock

Sedimentary rocks are formed by the deposition of material and its consolidation under the pressure of overburden. This generally increases the strength of the rock with age and overburden thickness, depending on its mineral composition. Elements of sedimentary rock are formed by mechanical action such as weathering or abrasion on a rock mass, transportation by a medium such as flowing water or wind and subsequent deposition. The origins of the rock will therefore partially determine the characteristics of the sedimentary rock. Weathering and erosion may proceed at different rates as will the transportation, affected by the climate at the time and the nature of the original rock. These factors will also affect the nature of the rock eventually formed, as will the conditions of deposition. Special cases of sedimentary rock include those formed by chemical deposition, like salts and limestones, and organic material such as coral and shell limestones and coals, while others will be a combination, such as tar sands and oil shales. Another set of special cases is glacial deposits, in which deposition is generally haphazard, depending on ice movements. Several distinct layers can often be observed in a sedimentary formation, although these may be uneven, according to the conditions of deposition. The layers can be tilted and folded by subsequent ground movements. Sedimentary rocks make up a very heterogeneous family with widely varying characteristics as shown in the table of sedimentary rock types, Table 4.

Metamorphic rock

The effects of chemical action, increased pressure due to ground movement at great depths, and/or temperature of a

32

rock formation can sometimes be sufficiently severe to cause a transformation in the internal structure and/or mineral composition of the original rock. This is called metamorphism. For example, pressure and temperature may increase under the influence of up-welling magma, or because the strata have sunk deeper into the Earth’s crust. This will result in the recrystallization of the minerals, or the formation of new minerals. The change in mineral composition means that the new minerals are stable at the higher temperature and pressure. This occurs without melting of the original rocks, and little change in the chemical composition. A characteristic of metamorphic rock is that it is formed without complete remelting, or else they would be termed igneous. The metamorphic action often makes the sedimentary rocks stronger and denser, and more difficult to drill. As metamorphism is a secondary process, it may not be clear whether a sedimentary rock has, for example, become metamorphic, depending on the degree of extra pressure and temperature to which it has been subjected. The mineral composition and structure would probably give the best clue. Due to the nature of their formation (see Table 5), metamorphic zones will probably be associated with increased faulting and structural disorder, making efficient drilling more difficult. Metamorphic rocks are also characterized by new texture and structure. The reason for a change in temperature and pressure may be due to heat from intruding magma, or because the rocks or sediments have sunk deeper into the earth’s crust. Compression and tension in the earth’s crust also play an important role during the metamorphic stage. Metamorphic rocks make up a large part of the earth’s crust. They are divided into three groups, depending on the degree of metamorphism: low, medium and high. In the first group there are only slight changes in mineral composition. Typical low-grade minerals are chlorite, albite and epidot. At medium and high metamorphism many new minerals are



Typical metamorphic rocks Rock type

Original rock

Degree of metamorphism

Amphibolite Mica schist Gneiss Green-schist Quartzite Leptite Slate Veined gneiss

Basalt, diabase, gabbro Mudstone, greywacke, etc Various igneous rocks Basalt, diabase, gabbro Sandstone Dacite Shale Silicic acid-rich silicate rocks

High Medium to high High Low Medium to high Medium Low High

Marble

Limestone

Low

Table 5: Typical metamorphic rock types and their origin, followed by the degree of metamorphism that is needed.

formed, for example, sillimanite and garnet. Due to the strong re-crystallization, all primary textures are destroyed, and in many cases it is very difficult to determine the primary rock. Metamorphic processes often make the rock denser and harder and more difficult to drill. Foliation is a kind of layering which is a characteristic feature of many metamorphic rocks. When rocks recrystallize under pressure from one direction, platy minerals like mica are orientated in layers perpendicular to the source of pressure. This results in banded or foliated rocks. Another type of metamorphic structure is lineation, where elongated crystals in the rock are oriented in the same direction, resulting in a cigar-like structure. Very often, the metamorphic rocks are named after the parent rock. Metamorphosed sedimentary rocks are called metasediments and volcanic rocks metavolcanites. Some examples of metamorphic rocks are given in Table 5. Quartzite is a very hard rock formed by the metamorphism of pure sandstone. Schist is a common metamorphic rock of medium to high grade. This rock is often named after the most common mineral, for example: mica schist; and chlorite schist. Marble is a well-known metamorphic rock formed from re-crystallized limestone. But there are other examples too of metamorphic rocks that, unlike the aforementioned, did not originate from sedimentary rocks. Igneous (magmatic) rock types can also undergo the process of metamorphosis. Gneiss is a high-grade rock type that is originally igneous rock which has undergone metamorphosis. In addition, as shown in Figure 4, gneiss is an example of how magmatic rock can skip over the sedimentary phase in the process of metamorphosis.

Macroscopic rock properties include slatiness, fissuring, contact zones, layering, veining and orientation. These fac-

Faults can consist of a single fracture plane, but it is more common that parallel fractures are created around a fault zone, which results in a shearing zone. Faults or fractures where the surrounding rock is crushed to small fragments are known as crush zones. The quality of the parent rock that will form the structure around the underground openings can be a major factor in determining the feasibility of a tunnel excavation, mainly because of their effect on the degree of support required. The tendency of rock to fracture, sometimes unpredictably, is also important to determine factors such as rock support requirements and the charging of peripheral holes to prevent overbreak. The procedures for minimizing overbreak and maintaining the contour design are strict and good results will yield benefits in terms of production and safety. Minimized overbreak will prevent the excavation of too much waste rock and a good contour preserves the structure and facilitates rock support. It is clear that rock structures, and the minerals they contain, can result in a wide variety of possible tunneling strategies. Obviously, the more information that is gained, the better the chances of success. If uncertainties occur in terms of unforeseen ground conditions and factors such as excessive water ingress, the advantages provided by modern tunneling equipment will be lost as drill rigs and other machines will be forced to stand idle. To avoid these situations it is vital to carry out an adequate amount of exploratory work to establish rock qualities in and around the site. Information from surface exploration drilling and geophysical methods of investigation are normally


33

Rock classification

Macroscopic rock properties

tors are often of great significance in drilling. For example, cracks or inclined and layered formations can cause hole deviation, particularly in long holes, and have a tendency to cause drilling tools to get stuck, although modern drilling control methods can greatly reduce this problem.


Rock drillability is determined by several factors including mineral composition and grain size, hardness, brittleness and crystal habit, if any. In crude terms, rock compressive strength or hardness can be related to drillability for rough calculations, but the matter is usually more complicated. The Norwegian Technical University has developed the Drilling Rate Index (DRI), the Bit Wear Index (BWI) and the Cutter Life Index (CLI). The indices are determined by the rock properties, brittleness, surface hardness and wear capacity and are indirect measures for the drillability of rocks. The DRI is assessed on the basis of two laboratory tests, brittleness and surface hardness. The penetration rate can vary greatly from one rock type to another. It should be noted that modern drill bits greatly improve the possible penetration rates in the same rock types. Also, there are different types of bits available to suit certain types of rock. For example, Secoroc special bits for soft formations, bits with larger gauge buttons for abrasive formations, and guide bits, steering rods or retrac bits for formations where hole deviation is a problem. The BWI, or Bit Wear Index, gives an indication of how fast the bit wears down, determined by an abrasion test. The higher the BWI, the faster the wear. In most cases, the DRI and BWI are proportional to one another. However, the presence of hard minerals may produce heavy wear on the bit despite relatively good drillability. This is particularly the case with quartz, which has been shown to increase wear rates considerably. Certain sulphides in orebodies are also comparatively hard, impairing drillability. The macroscopic rock properties, visible to the eye, give engineers a first clue as to whether blastholes can be drilled with good results.

supplemented by probe or core drilling conducted from an underground position like a tunnel heading. Modern computer software can also assist with processing the vast amounts of data and to deduce the suitability of various excavation methods for the rock that is likely to be encountered.

Rock classification

In order to systematically determine the likely excavation and support requirements, the amount of consumables required, and whether a particular method is suitable, a number of rock classification systems have been developed. These are generally oriented to a particular purpose, such as the level of support required, stand up time for a defined opening, or the rock’s drillability. The methods developed to assess drillability are aimed at predicting productivity and tool wear. Factors of drillability include the likely tool penetration rate in proportion to tool wear, the stand-up qualities of the hole, its straightness, and any tendency to tool jamming.

34

Another classification system being used by Atlas Copco is designated Diarot. It is aimed at calculating penetration rates and the bit wear for different rock types using a wide range of rock drills and tools. The rock parameters entered include unconfined compressive strength, brittleness and cerchar abrasivity index. Rock classification with respect to stability of openings plays a major role in all rock excavation and especially for underground projects. Commonly used rock classification tools are the Q-system (Barton et al, through the Norwegian Geotechnical Institute), Rock Mass Rating RMR (Bieniawski), and the Geological Strength Index GSI (Hoek et al). Bieniawski’s Rock Mass Rating incorporates the earlier Rock Quality Designation (RQD – Deere et al), with some important improvements taking into account additional rock properties. All of these give valuable guidance on the rock’s ease of excavation, and its self-supporting properties. In most cases, engineers will employ more than one means of rock classification to give a better understanding of its behavior, and to compare results. ◙


GEOLOGY

35

Rock classification


Figure 1: Geotechnical investigations include methods such as seismic refraction, core drilling and sounding, to determine the quality of the rock mass.

A matter of priority Most civil engineers agree that the key to a successful tunneling project lies in the quality of the pre-study. That doesn’t seem to stop some projects from deviating from the budgeted construction plan. Proactive geotechnical investigations, without shortcuts, means fewer costly surprises. Whenever a new tunnel is to be built, and the tentative location, type and length have all been established, the first and most important step in the design process is the pre-study phase, which requires a variety of methods for geotechnical investigations. The purpose of the pre-study is to reveal the type and nature of the rock mass and ground that will be encountered during tunnel construction, the presence of fissured zones or fault lines that may create special technical challenges, joint fillings, hydrogeological properties, soil conditions such as soft clays, stresses and more.

36

These factors are crucial in enabling the construction company to determine the most suitable excavation methods to use and to apply those methods in a way that will be effective, safe and meet the stipulated completion date. In addition, all of these factors combined will enable the company to build a cost calculation and establish a price tag for the contract.

Stepwise approach

As pointed out, having geological and geotechnical data available is a prerequisite when designing tunnels and caverns, which in turn calls for various field investigations and


GEOTECHNICAL INVESTIGATIONS

mapping to be carried out during the planning stage. The methods used and the extent to which investigations are carried out depend on the geology of the area and the type of project planned for. Subsea tunnels, for example, usually require more extensive, and thereby more costly, investigations compared with tunnels located on land where there is plenty of rock overburden. Geotechnical investigations are carried out in a number of steps. The advantage of this stepwise approach is that unworkable or unrealistic alternatives can be excluded before any extensive and costly investigations are initiated. In Norway, to mention one example, at least three steps are commonly followed. Feasibility study During the first step of the investigation, different ideas and possibilities are considered. The geotechnical investigation is usually limited, and its aim is often to find out if the project is possible and if it can be accomplished within reasonable costs. If satisfactory geological maps of the area do not exist beforehand, some geological mapping will be necessary at this stage. Seismic measurements or drilling may also be required, for example, in order to check if the rock overburden for the tunnel is sufficient. Principal design The recommended possibilities from the feasibility study are evaluated in detail, and a final location for the tunnel is selected for further planning. The main geotechnical investigation is now usually carried out, which is the goal of geological field mapping, seismic surveys, drilling, etc. Detailed geological maps and vertical sections are prepared and project costs are calculated, usually with an accuracy of ± 20%. Detailed design During this stage, the chosen project area is evaluated in detail. Accurate cost calculation is carried out, and construction drawings are prepared. Most of the geotechnical investigations have usually been finished prior to this stage, and only special attention is paid to individual zones, tunnel entries, etc. The tender documents are now prepared. The responsibility for conducting pre-studies and geophysical mapping falls on the shoulders of geologists and the exploration contractors they employ. The work is mostly performed by an independent firm of engineering consultants, except in cases of BOT contracts (Build Operate Transfer) when the construction company will probably choose to do the prestudy as well.

Field mapping

The field mapping method is employed at the initial stage of investigations and involves the careful study of all rock that is visible from the surface (outcrops) in a defined area surrounding the potential tunneling site. The purpose of field mapping is to provide a geological description based on rock mechanics data that is collected, including rock types, fissures and cracks. The results from field mapping will provide a general overview and a basis for more advanced investigations, such as geophysical measurements and drilling. For some smaller projects, however, field mapping may be the only type of geotechnical investigation that is required.

Geophysical measurements

From field mapping, it is only possible to observe the surface of any given outcrops, meaning rock that is visible from the surface. To get a physical picture of the underground, geophysics can also be employed with measurements that provide information on rock mass quality and the thickness of the overburden. A plan for geophysical measurements should be based on a geological map. The choice of method


37

Rock classification

Pre-study investigations will normally involve the use of three methods: field mapping, geophysical measurements and drilling. It is also important to conduct desktop studies, which implies the search for documented information from previous projects and relevant sources.

Core drilling involves the use of diamond drilling equipment that extracts samples of rock in cylinder-shaped cores.


N653KL N652KL N651KL

Figure 2: A wide range of geotechnical methods are often employed in combination, as shown in this 3D illustration. Coupled with data from various classification systems, the gathered information will result in tunnels being divided into different sections where individual rock reinforcement systems are planned.

for geophysical measurements will depend on the geological condition and need for exactness, which may change during the investigation, but the seismic refraction and reflection method is very common.

lacking. Using electrical measurements, it is possible to measure potential and current electromagnetic fields that occur naturally in the ground or that are induced by, for example, excavation work.

Seismic refraction is useful for the interpretation of the overburden for a tunnel. It involves the use of seismic transmitters and receivers, coupled with data processing hardware. This equipment is used to generate shock waves, and the various seismic velocities can be measured to enable an approximation of the geology and an estimation of the rock mass quality, even at great depths for deep-seated tunnels. However, the refraction method is not possible if the rock layers are reversed, in other words if soft rock layers are located underneath hard rock layers.

Variations in the resistivity of soil and bedrock produce variations in the relation between the applied current and the potential distribution as measured on the surface. This may reveal information concerning the composition, extent and physical properties of the subsurface materials. The resistivity depends on the pore water, which enables the porosity and fracturing of the rock to be determined. In this way, the electrical measurements can be used as a complement to or instead of seismic refraction during the geotechnical investigation phase for tunnels and caverns.

The accuracy of the seismic method depends on the placement of geophones and their spacing, as well as the direction of the seismic profile in relation to the geological structures. For best results, it is recommended that seismic profiles are placed in different directions. It is also good practice to measure the profiles both in parallel and at an angle to the tunnel line. When critical areas are indicated, such as soft rock or soil, exploration holes are drilled to verify the data that is

38

Drilling

As geotechnical investigations are an expensive and time-consuming process, these are rarely performed at random. When it comes to drilling, two types of drilling methods are typically employed: sounding and sampling. By sounding the resistance of a drilled hole, the various soil cover layers and, their thickness and sequence can be determined, thereby indicating the



Probe drilling Electromagnetic survey Refraction seismic

N

Ground water level Core drilling

N651KL

N652KL

N653KL

CHAINAGE RMR Q-VALUE SUPPORT CLASS

0+000

1+000

2+000

3+000

4+000

Figure 3: A typical blueprint for a tunnel based on geotechnical investigations data and rock classification systems.

location of the rock surface. If more detailed data is required, such as rock mass quality, core sampling will be the next step, which involves the use of diamond drilling equipment that can extract samples of cylinder-shaped cores, collected in drill core barrels. Due to the increased complexity in tunnel designs, it is rare today that tunnels are constructed without core analysis in the pre-study phase. At the same time, core drilling is an expensive undertaking and should be planned carefully. Holes should be placed where they can give the most valuable information, especially in weakness zones.

Describing rock mass and ground conditions from a technical point of view is not an easy task. For this reason, engineers often prefer to use numbers rather than adjectives, which has led to a number of classification systems being employed around the world. They are instrumental in highlighting the parameters that are crucial for tunneling projects, and among the most commonly used systems are: • The Q system: Developed by Barton et al (1974) of the Norwegian Geotechnical Institute. The Tunneling Quality Index, also known as the Q system, was based on the evalu ation of a large number of case histories of underground excavations. It is widely used to determine rock mass char acteristics and tunnel support requirements from an empiri cal standpoint. The Q system expresses the quality of the rock mass in the so-called Q-value. • Rock Mass Rating (RMR): First published in 1976 by Bieniawski, the RMR classification system focuses on the estimation of strength of rock masses, and it has since been refined as more records have been examined. A key benefit of RMR, as with the Q system, is that it provides an empiri cal study of fractured rock.


39

Rock classification

Core samples are taken continuously along the hole, and in addition to samples, other reconnaissance testing is carried out, including hydrogeological measurements. Tests that measure the permeability of rock mass are of particular importance. If the rock quality is poor during sampling, core loss may occur. In these cases, video inspections of the drilled holes may be useful. The holes can also be used to reaffirm geophysical measurements and to conduct stress measurements. Rock stress has a direct impact on the stability of tunnels and caverns and can be measured in various ways. Overboring and hydraulic splitting are two common methods.

Classification systems


Core samples must be retrieved in one piece to enable accurate analysis of the rock mass. Drill rigs used for this purpose usually feature a wire line device, or "core catcher" which lifts the core sample to the surface, eliminating the need to pull up the heavy drill pipe from the hole.

• Geological Strength Index (GSI): Concentrating on the description of two factors – rock structure and block surface conditions – the GSI system (Hoek et al, 1995) is used to estimate the peak strength parameters of jointed rock masses. In applying these systems, the rock mass is divided into a number of structural regions, and each region is classified separately (see Figure 2 and 3).

Continuous reports

After the contractor has been chosen, the construction period begins. In some cases there will be a need for supplementary geotechnical investigations during the construction period. This may involve drilling or geophysics data gathering ahead of the tunnel face to investigate rock overburden or weakness zones. In subsea tunnels, such investigations may be warranted as measurements from the sea can be difficult and expensive. Geologists usually work on the project during the construction phase as they continue to map the tunnel and provide advice regarding rock support and avoiding water ingress. A final report must always be prepared in order to sum up the experiences, which may be useful for future projects.

Unwanted surprises

If there is one thing that is rarely appreciated by tunneling engineers, it is geological “surprises”. Unexpected conditions

40

during construction can turn a perfectly good project into a “nightmare” characterized by disruption in the workflow, tough technical challenges, higher costs and major delays, which may involve financial penalties. These surprises may also have a negative impact on safety, both for the workforce and also for nearby surroundings and structures. Yet there are countless projects carried out around the world each year that go “off plan” in one way or another. At worst, there are cases where reality has deviated on almost every level with the information provided by the pre-study. Today, experienced companies habitually build a margin for pre-study error into their calculations. The question is, can the reliability of pre-studies be improved?

Cost vs accuracy

One root of the problem lies in the way tunnel projects are designed and commissioned. In most countries, the principal is a public authority, typically a national transport administration or local roads and railways municipality. It is the public body’s duty to keep costs as low as possible in the interests of the taxpayer. The pre-studies commissioned by these bodies are often limited in time and budget, and engineering consultants are obliged to keep their work within these parameters. It is debatable whether this system is the best. In most cases where tunnelers have run into difficulties, pre-studies have been insufficient. In the hard rock region of



Scandinavia, for example, it is not compulsory to employ all three exploration techniques. Neither are there any rules that state that investigations must be made at specific intervals along the entire length of the tunnel. Lastly, there is little or no correlation between the total project cost and the amount of money that is allocated to the pre-study. Clearly, if only one million dollars is allocated to a pre-study for a project costing several hundred million dollars, it would be unreasonable to expect it to provide a very comprehensive analysis of the project site. Considering the huge disruption and additional costs that are caused by insufficient prestudies, another million dollars allocated to the pre-study would seem a small price to pay to maximize the reliability of the analysis.

Finding the right balance

Logically, the fewer geotechnical investigations that are carried out, the greater the unreliability and the higher the final cost of the project. To reverse this situation requires establishing a good balance between the extent and scope of exploration work commissioned and the size, complexity and cost of the project. When it comes to establishing the nature of the rock mass – which is the tunnel builders first and most important consideration – core drilling is undoubtedly the most reliable form of investigation. The problem is not as great when tunneling in urban areas as it is in the countryside and especially remote locations. In and around cities, there are usually many tunnels that have been driven already. Data from these projects is available, and although pre-studies must always be carried out, comparisons, assessments and reasonable assumptions can be made based on experience. In the countryside, on the other hand, where little or no information is available, extensive prestudies based largely on core drilling are a must. This is especially important at sites where the nature of the rock mass is notoriously unpredictable, such as in high mountain regions of the Himalayas, the Swiss Alps or the Andes. Here, extreme rock compression, squeezing ground, massive fractures, voids and other conditions can present extraordinary challenges.

When core drilling in confined spaces, the Atlas Copco Diamec 232 is a suitable option as it is small and flexible


41

Rock classification

For example, it is essential that the specified shape and size of the tunnel – the tunnel profile – is maintained at all times. If the profile is deformed by squeezing ground, it will have to be recreated, and this means increased use of sprayed concrete, rock bolts and steel arches, which increases costs and work time. Core drilling is also the most viable method of exploring rock and soil in areas where a tunnel route is designed to pass under water. In this case, the drill rig is set up on land, and the drillstring can be steered to retrieve cores at angles beneath the bed of a river or lake and even take cores horizontally. ◙

y

x

Figure 1: When a tunnel opening is excavated, stress fields are redistributed in the surrounding rock.

Understanding how rock behaves

Constructing a tunnel in a safe and sustainable way requires a thorough understanding of the characteristics and behavior of rock and rock mass and how they respond to force fields in their physical environment. The science of rock mechanics is a complex world full of fascinating, natural phenomena. But for the modern tunneling engineer, it has just one purpose – to provide a platform for safe and sustainable reinforcement. The design of the rock support plan has three important criteria to fulfill. Firstly, it has to provide tunneling engineers with a safe environment in which to work. Secondly, it has to give the structure

42

long-term stability so that it will be safe to use for many years into the future. And thirdly, it has to be economically viable. Rock, contrary to popular belief, is by no means inanimate; it is living material. In its natural, in situ state, rock is constantly moving and reacts in a variety of different ways whenever it is disturbed or disrupted by force fields. These changes can


ROCK MECHANICS

be natural or induced by man through, for example, mechanical excavation. This means that tunnel planners and engineers are highly dependent on qualitative facts that underpin their decision making process regarding localization, dimensioning, excavation sequence and surveys of caverns, tunnels and shafts. Taking the right decision at the right time is paramount and will often have large economic consequences. To a large extent, this has been a driving force for the development of rock mechanics science. Rock mechanics provides a basic knowledge of the characteristics and behavior of rock and rock mass. But more importantly, it enables tunnel planners to evaluate how a given rock type, or different combinations of rock mass, is likely to react to various forms of excavation. The information regarding rock characteristics is gathered from rock samples. Altogether, the studies enable tunnelers to make a reasonably accurate assessment of the prevailing rock conditions that will determine the type of challenges that the engineers can expect to encounter during the excavation process. The fundamental issues to be addressed are: • Definition of the structural fabric of the rock mass, including aspects joints, faults and shear zones • Evaluation of the mechanical parameters of the intact rock and structures • Identification and quantification of the failure modes based on stress and structural analysis • Influence of the excavation sequence • Design of the rock reinforcement itself • Virgin stress situations • Water flow and water pressure

In situ and induced stresses

Rock at depth is subject to stresses resulting from the load of the overlying strata and from locked-in stresses of tectonic origin. When a tunnel opening is excavated, the virgin stress field is disrupted and redistributed in the rock surrounding the opening. (see Figure 1) Knowledge of the magnitudes and directions of these in situ and induced stresses is an essential component of tunnel excavation since, in many cases, the strength of the rock is exceeded and the resulting instability can have serious consequences for the tunnel openings.

Failure mechanisms

It could be said that stresses, rock strength and rock structures are the three most important factors affecting the stability of any excavation in natural strata material, and that a combination of various stress regimes, plus rock fragmentation and water pressure will dictate the excavation process. Tunnelers need a thorough grasp of ground conditions before rock support, such as bolting, can be installed in the best possible way.


43

Rock classification

Rock stress intensity varies from very low to very high, and the discontinuity pattern varies from massive rock to small

ROCK MECHANICS

Heavily jointed rock

Jointed rock

Massive rock

Low stress levels

Massive rock subjected to low in situ stress levels. Linear elastic response with little or no rock failure.

Massive rock, with relatively few discontinuities, subjected to low in situ stress conditions. Blocks or wedges released by intersecting discontinuities, fall or slide due to gravity loading.

Heavily jointed rock subjected to low in situ stress conditions. The opening surface fails as a result of unravelling of small interlocking blocks and wedges. Failure can propagate a long way into the rock mass if it is not controlled.

High stress levels

Massive rock subjected to high in situ stress levels. Spalling, slabbing and crushing initiates at high stress concentration points on the boundary and propagates into the surrounding rock mass.

Massive rock, with relatively few discontinuities, subjected to high in situ stress conditions. Failure occurs as a result of sliding on discontinuity surfaces and also by crushing and splitting of rock blocks.

Heavily jointed rock subjected to high in situ stress conditions. The rock mass surrounding the opening fails by sliding on discontinuities and crushing of rock pieces. Floor heave and sidewall closure are typical results of this type of failure.

Figure 2: Stability challenges as a consequence of stresses and rock structure. Source: Support of Underground Excavations in Hard Rock, Hoek E., P.K. Kaiser and W.F. Bawden. 2000, Balkema.

cubic structures or rock that has high schistosity. Massive rock will possess most of the intact rock strength, but will also accumulate load and can fail violently under certain conditions (see Figure 2). Very fractured rock will tend to yield to stresses and often deforms in a problematic manner. It should also be noted that the shape, size, sequence and type of excavation affects the way rock and rock mass will respond and should be taken into account. Among the most common failure mechanisms are stressinduced failures such as tensile failure, spalling, shear failure and rock burst, and structurally controlled failures such as sliding along joints, crushing of joints or rotation of blocks. Tensile failure occurs when tensile strength is exceeded and stresses influence the rock mass in one or more directions.

44

The failure is preceded by microfissures that later converge to form a complete failure area. This is manifested as a rough failure surface and is most common in walls in larger/higher rock caverns where the major principle stress is horizontal. Spalling occurs with uniaxial compressive pressure load and involves thin slices spalling in a direction parallel with the main stress direction. Splitting or cleaving is common in brittle, homogeneous rock that is exposed to high stresses. It occurs close to the tunnel’s boundary, normally in the roof in those cases where the main primary stress is horizontal. When structural rock failure occurs due to shearing, it is simply called "shear failure". This process is normally created by three axial loading. The failure starts with the activation of existing defects in the rock and the appearance of tensile failure fissures parallel with the principle stress line, similar to spalling. Rock burst is, in fact, not a failure mechanism by definition. Instead it can be defined as an induced seismic event as a result of tunneling (or mining) that damages the rock in excavated areas. A seismic event is the sudden release of potential or stored energy in the rock, creating a shock wave that causes damage to underground structures. In a wider perspective, the term rock burst is used as a collective description for failures that occur suddenly and in an explosive fashion. This form of failure normally starts with spalling, but the process is fast and often leads to considerable damage inside the tunnel. The phenomenon mainly occurs at great depth where the primary stresses are greater. For tunnels near the surface, seismicity and rock burst occasionally need to be taken into account when dimensioning, particularly when you have to deal with high horizontal stresses or excavation near steep slope surfaces. Sliding along a joint means that the shear stress exceeds the strength of the joint. Crushing occurs when the compressive stress exceeds the compressive strength. Rotation of the block takes place if the load induces a bending moment, causing a tensile stress in a joint with no tensile strength.

Gravity driven wedges

With openings excavated in jointed rock masses at relatively shallow depth, the most common types of failure involve wedges falling from the roof or sliding out of the side walls of the opening. These wedges are formed by intersecting structural features, such as bedding planes and joints, that separate the rock mass into separate but interlocked pieces. When a free face is created by the excavation of an opening, the restraint from the surrounding rock is removed. One or more of these wedges can fall or slide from the surface if the bounding planes are continuous or rock bridges along the discontinuities are broken, as shown in Figure 3.


ROCK MECHANICS

1 2

3

1 2 3

Tunnel with small coverage area Coredrilling hole Tunnel with large coverage area

Figure 3: If bounding planes are continuous, or rock bridges along the discontinuities are broken, one or more wedges can fall or slide into the excavation area.

Figure 4: The size and shape of potential wedges depend on the shape and orientation of the openings.

Unless steps are taken to support these loose wedges, the stability of the roof and walls of the opening may deteriorate rapidly. Each wedge, which is allowed to fall or slide, may cause a further reduction in the restraint and the interlocking of the rock mass and this, in turn, will allow other wedges to fall. This failure process will continue until natural arching in the rock mass prevents further unravelling, or until the opening is full of fallen material.

techniques can be used in producing these calculations. The most common of these are:

The size and shape of potential wedges in the rock mass surrounding an opening depend on the size (see Figure 4), shape and orientation of the openings with respect to the orientation of the significant discontinuity sets.

Empirical design is based on experienced interpretations of the reinforcement need. This design technique should therefore be coupled to a system of rock characterization and/or classification as these systems are often based on several well-documented projects.

The stresses that exist in the rock mass prior to disruption in the form of excavation, are related to the load of the overburden rock and on the topography, but also on the rock masses’ geological history. Construction causes a section of the rock to be removed which leads to a redistribution of the stresses in the rock mass, and these new stresses depend on the stress conditions prior to construction. High stresses in the rock mass prior to disruption can therefore cause high stresses in the excavated area which may lead to failures. The stresses that occur in undisturbed rock are normally referred to as virgin (or in situ) stresses, while those that exist after disruption are called induced stresses.

In the tunnel planning, construction and management processes place different demands on dimensioning and several

• Empirical design and rock classification • Analytical calculation • Numerical models

Empirical modeling

The empirical technique can be used at an early stage in the project for designing the reinforcement and as a complement to analytical/numerical models. However, the empirical technique should always be complemented with analytical and numerical models for reinforcement design.

Analytical modeling

Analytical calculation can, for example, be based on relatively simple calculation models in order to estimate the required thickness of the sprayed concrete, taking into consideration the volume of the rock which can fall out between bolts, or in order to calculate the bolting requirement for securing loose rock fragments in the tunnel roof. Another example of an analytical calculation method is compressed arch in blocky rock mass and the Voussoir beam theory in blocky rock masses.


45

Rock classification

Dimensioning

1 Tunnel with small coverage area 2 Coredrilling hole 3 Tunnel with large coverage area

ROCK MECHANICS

Using tools such as numerical modeling, stress regimes can be predicted and excavation sequences optimized.

Numerical modeling

In many cases, tunnel geometries or load conditions are more complex than the data that can be ascertained from analytical methods. Long term excavation planning can, therefore, benefit from detailed analysis such as numerical modeling and 3D visualization. Stress regimes can be predicted and excavation sequences optimized to keep the stress level at a comfortable level: not too high to create seismic events, and not too low to create major structural instabilities. Apart from being able to study more complex geometries, and to describe the various aspects of rock mass, various rock reinforcement elements can be included in the numerical modeling. These include bolts, sprayed concrete, concrete and more. In this way, the combined behavior of rock mass in a tunnel that has been reinforced can be properly analyzed. Numerical modeling can be used for both stress- and deformation analysis.

Follow-up and control

It is important to remember that dimensioning of, for example, rock reinforcement, cannot be regarded as complete until the tunnel itself has been completed. In other words, true

46

verification of the bearing capacity is only possible during construction using observations, mapping, testing and measuring. Geological mapping should be carried out continuously throughout the excavation process. It should include rock mechanics information (e.g. via systems for rock characterization) and be complemented by visual inspections of the conditions in the tunnel, including the reinforcement. Testing of the support elements (e.g. pull tests) should be carried out according to specific programs which can be produced during construction. Monitoring of any deformations that arise during excavation provides a valuable opportunity to verify the dimensioning calculations and associated reinforcement design. If the deformations deviate from the projections, there is often a possibility to adjust the reinforcement work during the construction stage. A detailed measuring program should be established before the tunneling is started and the choice of excavation method should be guided by the extent of measuring that is required. ◙


47

Rock classification


Planning for new tunnels is a rigorous step-by-step process that requires a thorough knowledge of ground conditions, the excavation method, cost scenarios and potential risk factors.

A multi-phased process From conception through to construction, civil tunneling projects are developed according to a well-defined, multi-phased process. Meticulous attention to detail at every stage is a must to minimize the risk of costly errors when work gets underway. Irrespective of the type of tunnel to be constructed, a great many parameters have to be taken into consideration before work can begin, and this process must be allowed to take time to avoid errors and unnecessary costs further down the line. The process starts with the project owner who is responsible for defining the tunnel’s location, route and purpose. In most cases, the owner will also be responsible for carrying out preliminary studies to determine feasibility and potential methods of construction. This will result in a document that serves as a solid foundation for decision-making in the

48

continued planning and implementation stage, including the procurement of suppliers and sub-contractors. At the next stage, the bidding process, tunneling contractors are obliged to demonstrate the same high level of planning integrity, in many cases even higher, in order to be considered for the contract to carry out the work. And their proposals need to be meticulously matched with the type of contract that is being offered. As shown in Figure 1, there are four contract forms that are common for most tunneling projects.


TT3_1-Tunneling

PLANNING FOR NEW TUNNELS

PROJECT FLOW Proposal

Feasibility

Surveys

Construction Tender document documents

Bidding process

Construction

BOT (Build Operate Transfer)

DB (Design Build)

Turnkey

DBB (Design Bid Build)

Delivery

Testing

Delivery

Operation

Transfer

Delivery

Colored lines indicate the contractor´s responsibilities

Figure 1: The phases of tunnel construction and typical contract forms.

These are: • Build Operate Transfer (BOT): a joint venture whereby the responsibility for the detailed design, construction and financing is shared. The joint venture is given the conces sion to maintain and run the tunnel for a limited period and to generate income from operation of the tunnel. • Design Build (DB) and Turnkey: the design and construc tion are undertaken by a single entity known as the design builder, or design-build contractor. In both DB and Turnkey contract forms, the contractor is responsible for all of the work, including financing up until completion of the project. • Design Bid Build (DBB): a traditional contract form where by the project owner engages separate contractors and suppliers for the design and construction work. The DBB contract differs from the other contracts in several ways. For example, the delivery method is based on three main phases. These are, in order: the design phase, the bidding (or tender) phase and the construction phase. In this chapter we focus on the basic, multi-phased process that the tunneling contractor will generally need to follow, bearing in mind that these may differ due to local laws and practices.

Know the ground, know the method

The contractor’s main concern is with the type of geology through which the tunnel is planned to pass. Knowledge of the characteristics of the rock and surrounding ground conditions is crucial in order to select the most suitable method of construction.

The concept

Step one is to study the basic concept provided by the project owner. This will usually include an analysis of the motives behind the design, such as the need to speed up public transportation or expand municipal drinking water or wastewater treatment systems. Alternatively, the tunnel may be just one element within a much bigger development, such as to move surface-based power lines or parking lots underground, to free up land for housing, or to expand a hydropower plant or oil and gas depots. It may even be intended to form a section of a complex underground repository for nuclear waste. In addition to this, the concept will most likely include information on all known obstacles and challenges along the alignment such as mountains, rivers, bridges, geological fault lines, groundwater or underground structures and installations.

Surveying and feasibility

A crucial part of the owner’s pre-study work will involve geological surveys and ground investigations at the site. The purpose is to reveal the type and nature of the rock mass and ground that will be encountered, including the presence of fissured zones or fault lines, joint fillings, hydrogeological properties, soil conditions, and so on. These factors are crucial in order to establish the most suitable method and equipment that will allow the tunnel to be excavated effectively, safely and on time. The in-depth feasibility study will provide the basis for assessing the construction phase as it will detail


49

The tunneling process

Most modern tunnel projects are normally developed stepby-step in the following phases: • The concept • Surveying and site investigations • Feasibility studies • Preparation of construction documents

• Preparation of tender documents • Tendering and bidding • Construction • Testing and delivery • Management and transfer (if applicable)


contractors will be required to complete in order to qualify to apply for subcontracts. Note that these questions to contractors will also be used to form the basis of the business relationships and types of cooperation that will later be proposed: i.e. they will act as the framework for the final tender application in which lead contractors are required to state which subcontractor structures and payment arrangements will be adopted in their bid. However, there are exceptions to this procedure depending on the contract form. If the tunnel project is set up as a BOT (Build Operate Transfer), a Turnkey project or a DB project (Design Build), the contractor will be responsible for the design and for developing the construction document.

Tendering and bidding

The tendering and bidding process may differ from country to country, but the procedure followed by most contractors is as follows:

A Boomer XE3 C drill rig on site during construction of the Goetschka Tunnel in Austria.

what needs to be done, stipulating all challenges and possible solutions. A wide range of methods is used to gather this vital information and the feasibility study is used as a reference throughout the planning stages. For more information on this, go to the section on geotechnical investigations, page 36.

Preparing the documents

When all of the facts have been ascertained, it is time to prepare the official documentation. Primarily this will consist of two documents: one to cover the project (Construction Document) and one for procuring subcontractors (Tender Document for contractors). The design phase and compiling the construction document is a complex process in which a great many technical details have to be incorporated and coordinated, including all of the findings of the geotechnical investigations. The final product will consist of technical descriptions and drawings, a bill of quantities (BQ), which details all materials, labor and their costs and is prepared by a quantity surveyor, as well as an extensive list of other related issues. The tender document for contractors will consist of the project description together with a list of questions that potential

50

• Prequalification: understanding the project conditions (envi ronmental and technical demands, time schedule, start date, milestones, completion date, penalties, site visits etc.) It is common for contractors to ask for prequalification and this is done by supplying documentation on experience from similar projects. Listing of capacities in the form of equip ment and staffing may also be required. • Risk analyses: financial, contractual, technical and geologi cal risks. • Project planning: how to proceed in light of the demands and risks, how the project will affect third parties, what capacity is required to meet the time schedule, what type of equipment is required, size of the crew. • Procuring estimates: subcontractors, material such as rock bolts, sprayed concrete, tunneling equipment, spare parts, service contacts, etc. • Estimating the project: content of the tender, prices, time schedule, description of the works, company SHEQ (Safety, Health, Environmental, Quality) document, resources, per sonnel and equipment, reference projects, alternative solu tions besides the tender document, tender bond. • Standard evaluation criteria: cost, technical description, project plan, organization, resources, environmental plan. • Negotiation: signing the contract, project startup. Attention to detail and accuracy cannot be over-emphasized in these steps and a rule of thumb is to do everything correctly from the beginning. This goes for developing the organization, selecting the methods, highlighting the demands placed on the company and informing the crew of their tasks so that they know what will be expected of them. When it comes to procurement, contractors should be wise in making purchases. It is advisable to look into the total cost of the project instead of at the individual unit prices. Suppliers



should be chosen carefully. Awareness of delivery times for equipment is crucial must be specified and the total cost of ownership should always be taken into account.

Starting up the construction

Once the contract has been awarded and construction is due to get underway, it is imperative that good planning discipline remains in place. What’s important at this stage is to ensure that the actual construction will adhere to the specifications of the contract with regard to time, cost and quality. To achieve this with as few deviations as possible, it is necessary to make sure that uncertainties and unpredictabilities can be dealt with swiftly and smoothly which, in turn, requires excellent cooperation between the project owner and the contractor. Experienced and skilled staff on both sides is also a must. Production needs to be planned in both the long and short term, purchasing plans for equipment and materials should be in place, and plans for the procurement of the necessary labor should be clearly defined.

Testing and delivery

Once the project is complete it will have to undergo a period of inspection and testing. Any observations or issues that may arise from the official Completion Inspection must first be addressed before delivery and final payments can take place. The contractor normally has to provide a guarantee period of a certain number of years, at the end of which there will be a Guarantee Inspection. Again, any issues arising from the Guarantee Inspection must be addressed, after which the contractor has no further obligations. Contract types vary when it comes to final delivery. For example, if the contract is based on a BOT (Build-Operate-Transfer) agreement, the tunnel will also be operated and managed by the supplier organization for a period of time, often three years, before being finally transferred to the principal owner.

Prerequisite for success

One prerequisite that will have a major impact on the outcome is the selection of equipment. The contractor that chooses to use tried and tested methods with equipment from recognized manufacturers with a solid track record in tunneling will be much more likely to win the contract. Conversely, the contractor that chooses to use equipment that may not be entirely suitable or wholly reliable is less likely to be successful.

Tunnelers celebrate the main breakthrough at the Lötschberg Base Tunnel in Switzerland.


51


It is important to add here that the choice of equipment is not only a matter of which drill rigs, loaders, rock bolts and ventilation systems to use. It is also a matter of obtaining the best package that will also include parts and services and experienced technical support in order to achieve the highest quality at the lowest total cost of operation. ◙

Every tunnel project is dependent upon a well-organized operation. This includes having skilled and trained personnel and a transparent flow of information, among other key factors.

Big wheels in motion People and teamwork are the keys to excellence in all tunnel projects. Having a solid operational framework in place is of the utmost importance, well before the very first hole is drilled. On time, within budget and a first-class result – the three-fold definition of successful tunneling can only be fulfilled with elaborate teamwork at every step of the way and where safety is also an ongoing and natural part of the process. Although it is true that the development of modern technology is changing the face of the tunneling industry day by day, people remain the most valuable asset of tunnel projects large or small and regardless of complex designs. Each team involved is an indispensable link in the chain that drives the great wheel of progress from day one to final delivery. As

52

such, it is important to emphasize that it only takes one missing link to jeopardize the schedule, resulting in increased costs. For this reason, it is important for project managers to begin the work of allocating personnel and setting goals at the earliest possible stage. Organization is about building a strong base for cooperation at every level by making full use of communication techniques that are at the heart of teamwork. This needs to be backed up by good training. Trained, skilled operators and technicians perform better, find their work more enjoyable and contribute to increased productivity. They


MANAGEMENT OF PROJECTS

know how to maximize the output from machines in a safe and sustainable way.

Sustainable workplace

Much like solving a puzzle, tunnels are constructed in a stepby-step process over extended periods of time in a confined and sometimes difficult environment. A tunneling site could involve anything from 20 people to more than a thousand in larger projects that involve several tunnels, with key functions spanning everything from drill and blast or TBM operators (Tunnel Boring Machine), tunnel designers, coordinators and surveyors to site superintendents, project managers and engineers for installations. To maintain a smooth operation, work procedures should be established well in advance of the first construction phase before the clock starts ticking in terms of schedules and costs when, generally speaking, every delay weighs the operation down. As a first step, a few fundamental parameters need to be established and adhered to including: • A safe working environment • Transparent flow of information • Trained operators and service personnel • A well-organized overall operation, including workshops/ maintenance • Employee development at local level • Readiness for unforeseen events A completely trouble-free tunneling process may well be a rare occurrence. Having said this, keeping staff members informed about the project’s mission, their roles and ongoing developments is a proven approach that boosts the positive odds considerably. Good communication through clear messages is a guiding principle that should permeate the entire organization. By focusing on clarity when designating assignments, you will avoid any overlapping of duties and tasks, which means reducing the risk of costly double-work. Furthermore, high-level information flow is far more likely to foster a spirit of participation among the team and enthusiasm for the task at hand.

Proactive culture

at the tunnel face. At the very least, a sustainable workplace will result in benefits such as less turnover of staff (satisfied people stay), the potential to develop an experienced organization, better control over risk/cost factors, and a foundation for long-term customer/supplier relations. Being proactive is also a crucial aspect of safety, which today is a constant concern for all construction companies. Safety is not something to be focused on now and again or whenever it seems appropriate. It is a never-ending process based on a desire for continuous improvement in order to safeguard the lives and well-being of tunneling professionals. A raised awareness about safety issues over the past decade has also had a large, positive effect on productivity levels.

Cyclical workflow

A high competence level is usually the most important factor for satisfactory completion of tunnels. This not only goes for site personnel but also for external contractors and sub-suppliers. At regular intervals, the entire team should be engaged in operational tracking by answering basic questions such as


53


In addition to strong communication, flexibility is recommended such as giving staff the possibility to influence the setup of daily routines. Another key element is to offer training on a continuous basis, leaving no one doubtful of their skills and capabilities. Experience shows that setting high goals, instilling a sense of shared purpose and showing consistency in management will stimulate a proactive culture. This means that challenges in the construction cycle can be dealt with more quickly and with a minimized impact

Continuous training intervals is a proven way of boosting safety and efficiency at the worksite.

MANAGEMENT OF PROJECTS

Operational tracking and assessment is increasingly carried out during construction, together with all personnel. This helps to identify SHEQ issues (Safety, Health, Environment, Quality) and alternative solutions to specific challenges.

what has been achieved, what the problems related to SHEQ issues (Safety, Health, Environment, Quality) are and how alternative solutions can be found, as well as the challenges in short term vs. long term planning. Once the above guidelines have been put into practice, a cyclical workflow can be introduced. This implies that everyone involved is both aware and well-prepared for the next step at any given moment in the tunneling process. Operational tracking also serves the purpose of boosting overall transparency at the worksite. It is increasingly common for tunnels to be assessed during their construction as this facilitates accurate backtracking of weakness zones and how they have been handled. Without this information, it will be much harder to plan for continued maintenance of sensitive areas as these may have been covered with a concrete lining prior to the tunnel becoming operational.

QA/QC protocols

Although each tunnel design is unique, setting high benchmarks for quality is a prerequisite for today’s high demands on tunneling projects. Greater understanding yields higher quality, and both drilling and rock support tend to be two major focal points. A driller, for example, needs to be not only fully prepared but also aware of his or her impact on the

54

quality of blasting, which, in turn, affects haulage operations. In addition, project managers should engage dedicated teams who can perform quality checks on a regular basis. Quality control (QC) is the term applied to a company’s own efforts to make sure that rules, specifications and best practices are adhered to and that promises to customers are duly delivered. Regular input and approval, however, is also needed from independent auditors. While universal QA/QC protocols are often adapted and tailored to fit the needs of individual tunnel assignments with their distinct challenges, there are a few important points that are generally followed. Checking of written routines, follow-up on routines, data gathering regarding all processes and tasks, economic followup on maintenance and tracking of Key Performance Index (KPI) are just some examples of important aspects. As clients are placing higher demands on the design and quality of tunnels as well as production processes and health and safety standards, which form the basis for ISO certifications, QA/QC programs are indispensable tools for future success in the industry. To conclude, a holistic approach and a cyclical workflow should be the overarching goal of an organization. It is the mechanism by which quality becomes a natural part of the overall operation, which maximizes the potential for meeting delivery targets. ◙


55



The Atlas Copco range of simulators provides a realistic on-site experience based on a wide variety of training scenarios.

A smarter way to go New equipment and new technologies put high demands on tunneling staff, regardless of their knowledge and skills. Getting equipment operators trained and fit for the challenge has never been easier. The importance of training can never be overemphasized. Trained personnel perform better, find their work more enjoyable and contribute to increased productivity. Having well-trained operators also increases overall safety in the workplace, which considerably reduces the risk of accidents and injuries. Familiarity with today’s high-technology methods is a basic requirement of all tunneling engineers, and some equipment manufacturers such as Atlas Copco offer a wide range of training programs to provide them with the skills they need. These days, the same requirements are also being placed on equipment operators who are not only expected to operate

56

their machines correctly and safely, but also required to have a broader understanding of their role in the process and the personal contribution they make to the success of the company they work for. The reason for this is twofold: the need for high productivity at the lowest possible cost and the fast pace of technological development which is constantly increasing requirements on contractors to offer the latest tunneling solutions. Against this background, no tunneling contractor today can afford to put an expensive piece of equipment, a drill rig for example, into the hands of an operator who is not fully trained for the task.


OPERATOR TRAINING AND SIMULATORS

Simulators for skills shortage

In the past, skilled labor was available in abundance. New recruits were relatively easy to find and were traditionally trained by the most experienced operators on the crew. Today, there is a worldwide shortage of skilled labor. New recruits are extremely hard to find and it is becoming increasingly difficult for contractors to find people on their own staff who can spare the time to train new recruits. This problem is being addressed in different ways in different countries, but the common goal is to find a solution that does not burden ongoing operations. In this context, the use of simulators for training purposes instead of real equipment and, to a great extent, outsourcing the training responsibility to external specialists are emerging as the smartest way to go.

The power of simulators

The advantages of this approach are considerable. Firstly, simulator training enables operators to be trained without disturbing ongoing projects or having to assign experienced operators to the job. Secondly, operators can be trained on the surface where they can learn and practice in an environment without disturbance from other activities. And thirdly, it eliminates having to put new operators in charge of expensive, high-technology equipment until they are fully qualified to take on such an important responsibility. This reduces the risk of machinery being damaged due to incorrect use and, more importantly, it can reduce the enormous costs associated with disruption to operations, time-out for unscheduled maintenance and repairs and, last but not least, accidents resulting in injuries to personnel. Another big plus is that trainees do not need to worry about the challenges of handling machines in a tunneling environment – with all the potential hazards that this involves – until they are sufficiently skilled and confident.

Tailor-made programs

The actual cost of training new recruits can be minimized since the training time required when using simulators can be substantially reduced. According to studies, training with simulators cuts the time it normally takes to get new drill rig operators up to speed by an average of 50%, which is a big advantage in terms of increased efficiency and operational capacity.

step-by-step courses to teach operators all of the skills they need in order to take full responsibility for their Atlas Copco equipment.

Virtual reality – a fun way to learn

The simulator part of the program has been especially successful. Here, the trainee operator gets exactly the same look and feel of the real machine. All procedures such as startup, drilling, tramming, drill plan handling and positioning are performed in exactly the same way as the real machine, giving a totally realistic experience. Another important advantage is that simulators are capable of producing and analyzing performance data, enabling trainees to improve their own performance and compare results with their fellow trainees in groups. This not only produces higher standards but is also a fun way to learn. Trainees can also go back and repeat any aspect of their training at any time, either to refresh a specific skill or to improve on weak areas. The range of such training simulators now available on the market is consistently expanding and in time will encompass most types of equipment for underground construction. In the future, as learning devices such as these become more widespread, contractors will be able to train new operators to a high standard with a minimal impact on their day-to-day operations and resources. And this, in turn, should impact on flexibility, productivity, safety and profits. ◙

MASTER DRILLER PROGRAM The Atlas Copco Master Driller program is a program that provides trainee drillers with theoretical and practical training in three steps. It combines e-learning or classroom training for basic knowledge and skills, as well as simulator training for practical, true-to-life learning in a variety of mining scenarios. This is then followed up by on-site training with an Atlas Copco specialist. After successfully completing all three levels – Bronze, Silver and Gold – the trainee is awarded a Master Driller Diploma.

Master Driller provides trainee drillers with three levels of proficiency – Bronze, Silver and Gold – and consists of


57


Recognizing the need to address the training issue, a number of equipment suppliers have been proactively developing their own tailor-made training programs to offer to their customers. A typical case in point is Atlas Copco’s Master Driller program, which is specially designed to match all of the equipment in the company’s range.

Well-placed and proper installations for water, compressed air and electricity go a long way to keeping tunneling projects on schedule.

A worthy investment for progress

To drive a tunnel is a tough job and basic components such as roads, electricity, ventilation and water are more than just essential requirements. Experience shows that good quality infrastructure is money well spent. Whether for roads and railways, hydropower plants, water and utility tunnels or underground storage, a reliable and well-maintained infrastructure is the lifeline of any tunnel construction. What is meant by “infrastructure” in a tunneling context? The answer is everything that is a fundamental need, including roads and ditches, electricity, water supply and waste

58

systems, ventilation, lighting, compressed air, communications technology and rescue chambers, to mention a few. Although some tunnel projects are more complex than others, all benefit from early investments in all of the above. The infrastructure is simply expected to function correctly from day one, and should any of these fundamental elements fail, the entire project will suffer in terms of lost time and cost.


WORKSITE INFRASTRUCTURE

Which equipment will be used and how will it be powered? How much water will be needed or pumped out? How much ventilation is needed and where in order to guarantee a safe working environment and minimize equipment downtime? As soon as a project moves from the tender phase to real calculations and planning, the answers to these questions can never be left in doubt.

Road maintenance

Good quality roads that are well maintained play a large role in achieving high utilization at the tunnel face. If roads are not dry and up to the desired standards, equipment will most likely be damaged, resulting in costly unplanned maintenance, and drivers and operators may well be put at risk. This means that the flow of construction traffic will be impaired by a slow mucking out process that not only breaks the time schedule but is potentially very costly. When constructing a road network, the choice of material should be made according to the site conditions. In nearly all environments, a well-packed road and a well-maintained ditch are necessary to ensure proper water drainage from the road body. If there are leakages from the tunnel roof, these should be prevented by grouting or by installing a drainage system leading the water down to the ditch. This is crucial because dripping water will eventually destroy the road surface and lead to expanding potholes and cracks. In access tunnels where frequent transport takes place over long periods, it can be well-invested money to surface the road with concrete asphalt, especially if there are steep inclinations or sharp curves.

Water supply

Most of the processes in tunnel construction, such as drilling, concrete spraying, grouting and bolting, require a continuous water supply and a wastewater management system. If either of these are wrongly designed, low pressure and poor water flow will result in a negative effect on progress at the tunnel face, especially with drilling. Supplying the right amount of clean water is often a challenge due to environmental issues.

The highest demand for water usually comes from drilling. One way of reducing consumption is to use water mist on

In addition to electricity, water and ventilation, compressed air is a required utility used for water mist during drilling, among other applications.


59


Here, it is highly recommended to recycle waste water in a treatment plant, which requires a thorough knowledge of water needs. Without an accurate design of the sedimentation system, particles that are too big will pass and damage the equipment. The treatment plant must also be set up according to existing environmental regulations.


R CHESCU AM E BE R

Figure 1: Rescue chambers must be strategically placed. Pipes, wiring and ducts must be installed professionally, fixed securely on roofs and walls.

the drill rig, a system where air and water are combined. Although water mist requires a bigger compressor, water consumption can be reduced up to 95%.

parameters, including ventilation, pumping systems, workshops, offices, the simultaneous use of equipment and more. It is also important to devise the electrical system so that it can handle peak load.

Waste water

In order to avoid any damage to the system, all cables, transformers and conduits must be located safely in the tunnel system. They need to be protected from both water leakage and from other moving equipment.

A well-designed waste water system handles both process water and any ingress of water from the surrounding rock and the surface that flows in via the tunnel openings. When designing the system, all the inflow criteria must be included and a pump chain should be installed with overcapacity in order to account for wear and tear of the pumps. It is important to consider the potential impact of a malfunctioning pumping system or a lack of extra pumps. Experience shows that excess water may not only flood the tunnel face but also destroy roads, with huge repercussions in terms of increased costs.

Electricity system

Power supply is another fundamental factor. The electrical system must be designed to take into account all consumer

60

Communications technology

Instant and effective communication is a prerequisite for short lead times between activities and in order to uphold steady progress at the face. In tunneling, this involves many types of installations such as radio communication, WLAN, tracking systems for personnel and equipment, and mobile telephony. The radio system is usually the primary tool for tunnel personnel to communicate with each other. It can be either an analog or a digital system, whichever suits the project best, so that help can arrive rapidly should any process go wrong or an accident occur. Access and tracking systems are instrumental for knowing which personnel and equipment are present



Figure 2: Poorly installed infrastructure leads to insufficient air flows, leaking pipes and potential hazard, resulting in delays and increased costs.

at any location, at any given time. These systems not only address emergency situations, but also help to increase the utilization of manpower and equipment. In a tunnel project, a continuous flow of data is transferred between equipment and people. This means that a reliable WLAN system is highly advised, which can also be used to manage the other communication tools mentioned above.

Compressed air supply

Looking at history, compressed air has mainly been required for handheld pneumatic drilling equipment, concrete spraying and ANFO charging. This, however, is gradually changing as hydraulic equipment in tunneling is increasingly employed with the water mist function, which is dependent on a certain supply of compressed air.

Comprehensive planning

Adopting a meticulous approach is crucial when setting up the infrastructure for a tunnel project. Eventual scenarios in the construction process must be scrutinized and calculated in order to avoid mistakes early on. For example, site managers need to assure that rescue chambers, electricity and water supply sources are not placed too far from the tunnel face. All it takes for costly downtime to occur is for an electrical cable to fail to reach a socket or equipment unit. Similarly, short distances are highly recommended for stockpiling materials, such as spare parts, drill bits, rods and bolts. Here, as the excavation progresses, it may be possible to take advantage of niches previously created for haulage equipment or rescue chambers. All available space near the production area should be utilized to its full potential. ◙


61


The current trend is to have onboard air compressors mounted on modern equipment, to avoid large compressors and pipelines underground. When external air compression is used, compressors are often located outside the opening and are connected to a system of steel pipes in the tunnel system. The air system should be mounted in a way that reduces the

risk of damages to the pipes. A badly maintained or damaged system results in insufficient air flow and pressure, as well as increased costs. The same applies to ventilation ducts, see chapter "Ventilation systems: Optimizing the air", p. 116

Taking a proactive approach toward service can make the difference between successful, on-time delivery and costly delays.

Preventive maintenance for maximum uptime

Keeping a close eye on your equipment’s wear and tear is an indispensable part of the tunneling process. This is where effective planning and reporting systems will have a striking effect on rapid action for any items that require attention. There is widespread appreciation among modern construction companies for the role of preventive maintenance and the impact it has on quality, safety, operational costs and delivery times for tunnel projects. This has become especially apparent in recent years with the constantly increasing level of technology associated with rock excavation equipment coupled with the growing scarcity of skilled labor. Preventive maintenance as a means of achieving maximum equipment uptime, avoiding unnecessary disturbance to

62

operations and reducing costly downtime is beyond dispute. The high availability of equipment that this provides is crucial for project reliability, which enables construction companies to follow their plans and meet their targets. As in many other industries, maintenance is equally important when it comes to facilities and infrastructure. Roads, workshops, ventilation, electricity, water supply, filtering systems and all other components in construction projects need continuous attention in order to safeguard productivity


MAINTENANCE

Maintenance of equipment should be as calculable as possible. All service data should be factored into the operational cycle of tunneling projects.

and provide a reliable, safe working environment. Although it is fair to say that a great deal of progress has been made globally in this area, there remains ample room for improvement.

Quality in all areas

In order to achieve maximum efficiency in service and maintenance, it should not be regarded as an isolated function but rather as an integral part of a process in which all components interact. The ability to monitor equipment performance and automatically compile statistics on wear and tear has enabled companies to optimize their service arrangements. This information highlights where the primary problem areas lie and enables preventive measures to be initiated efficiently and cost effectively. Simultaneously, the training of maintenance technicians has improved as more and more suppliers develop professional on-site training programs for their customers.

Maintenance planning

In order to capitalize on preventive maintenance processes and reduce disruptions to operations, contractors should ideally implement an efficient planning system with reliable data mapping. This, in turn, requires strategy and organization. The objective is to make maintenance and service as calculable as possible where precise outage time of all equipment can be counted into the tunneling operational cycle. A maintenance organization should always be established in accordance with the excavation strategy. It should measure key performance areas, maintain detailed records, and take into account everything from emergency breakdown repairs to planned component replacements and all preventive maintenance hours with the specified procedures.


63


With the development of more advanced underground equipment offering longer service life, the nature of maintenance work has shifted from repairs to component replacement. Removed components are often transferred to surface work-

shops for repair, and in some larger tunnel projects, contractors will utilize niches in access tunnels as temporary service bays. In addition, more and more suppliers of rock excavation equipment are offering full service agreements whereby expert maintenance service is provided on-site, 24 hours a day, 365 days of the year, allowing the customer to better focus on their core activities. On-site visits from maintenance experts and product specialists are a trend that is expected to continue.

MAINTENANCE

machine interruptions and 2 h external interruptions, the calculation will show the following:

Calendar time Planned idle time

Planned operational time

Preventive maintenance Machine interruptions

Available time External interruptions

Utilized time

Figure 1: Typical interaction between calendar time, planned operational time, available time and utilized time.

Whatever the underground project may be, benefits for both parties can be obtained from employing a system that includes the following: • Ratio of production vs. maintenance • Mechanical availability data • Equipment utilization • Mechanical reliability • Service tracking of components • Cost and trend reports • Backlog Management • Labor key figures Calculating the planned availability of equipment is an efficient way of achieving full capacity production at a tunneling worksite. In order to optimize the preventive maintenance cycle, a number of definitions and distinctions are normally adhered to, including the following: • Preventive maintenance: planned on a regular basis • Machine interruptions: unplanned downtime due to techni cal malfunction of equipment • External interruptions: operational downtime due to factors unrelated to machinery, including unforeseen ground condi tions, environmental issues, damage, complaints or logisti cal problems • Availability: percentage of planned operational time when the machine is available • Utilization: percentage of calendar time when machinery is in operation (utilized) • Stock availability according to long-term plan To illustrate with an example: of a 24-hour calendar time with 1 h of planned idle time, 1 h of preventive maintenance, 0.5 h

64

Availability Available time / Planned operational time = (24-1-1-0.5) / (24-1) = 93.5% Utilization Utilized time / Calendar time = (24-1-1-0.5-2) / (24) = 81.3% As shown in Figure 1, preventive maintenance is essential in order to secure maximum machine uptime and is particularly important for tunneling projects where automated or semiautomated processes are employed, such as blasthole drilling. It is also important for contractors to monitor and follow up on maintenance needs; how, when and why it is performed; and the results that a chosen system yields. A few basic requirements will include answers to questions such as: • Is there a clear division of responsibilities? • Are processes, procedures and instructions established and clear? • Are the targets and KPIs clear to all involved? • How are monitoring and reporting performed? • Is there a documented review process? • Is there an organized system for making improvements? In general, service and maintenance facilities for large tunnel projects are located on the surface in between site offices and the main access tunnel or worksite entrance. A rule of thumb is to find a strategic location at a safe distance from haulage routes yet in close enough proximity for maintenance to be carried out with maximum efficiency. Workshops need central power and water supply, lube stations and pump systems. It is also important that chemicals are used carefully and material safety data sheets (MSDS) are provided in an accessible location for all personnel. An approved process must be in place to respond to any possible liquid / chemical spillages and spill kits must be in place in suitable locations. The chosen storage location for liquids / chemicals should in no way pose a risk to the surrounding environment.

Statistical data and logistics

To achieve maximum equipment uptime, it is advisable to look at the whole tunneling process preferably using a maintenance planning software system that is synchronized with performance data for all machinery used at the worksite. Statistical data should be used to follow-up, eliminate bottlenecks and establish the most favorable conditions, including a well-drained, dry, safe and sustainable work area that also aids in the maintainability and lifecycle of cables and other sensitive equipment components. In addition to machine maintenance, road maintenance should be an ongoing process and should be regularly reviewed to


MAINTENANCE

Adopting procedures for preventive maintenance means that spare parts can be ordered in good time, which minimizes the impact of equipment downtime.

prevent major work on roads as well as machines. For example, when it comes to haulage operations, a well-maintained road will allow for safe and efficient transport of excavated rock from the tunnel face and reduce wear and tear factors on equipment, such as vehicle tires, transmission and suspension systems and frame components.

In this way, the forecasted requirements on service and maintenance both now and in the future will be sustained, which in turn will allow for the operation to better meet its planned production targets. ◙

PEAK PERFORMANCE Adopting a scheduled maintenance program is the best way to ensure that tunneling equipment is performing at optimum level at all times, thereby minimizing downtime, keeping productivity levels high, and avoiding costly repair work. Atlas Copco offers comprehensive and tailor-made service agreements for all its rock excavation equipment, covering everything from drill rig components and parts to rock drills and drilling steel.


65


For more information, please visit www.atlascopco.com

The Atlas Copco Boomer range is often used in drill and blast tunneling. It is equipped with a Rig Control System (RCS) so that vital drilling data can be monitored at a distance.

Seeing the big picture The ability to oversee the performance of an entire fleet of tunneling machines during operation is now a reality, offering significant improvements to productivity and efficiency. The possibility to monitor the performance of mobile tunneling equipment from a central point and in real time has been explored for many years. Not only would project supervisors be able to keep individual machines under constant surveillance, they would also be able to monitor their performance, identify potential problem areas and quickly react to any potential disruption in the excavation process before it occurred. The information could then be processed and correlated to create a truly proactive service and maintenance program that would result in considerable savings in terms of reduced downtime, increased productivity and faster completion. To many tunneling engineers, remote monitoring is still a thing of the future, but that doesn’t mean it is not available. On the contrary, a number of equipment suppliers have developed a variety of well-functioning systems, not least Atlas Copco,

66

whose proven Rig Control System (RCS) on tunneling rigs enables key data to be gathered, stored and analyzed on a continuous basis.

The next level

Atlas Copco has now taken this capability to the next level in a joint venture project with the automation and power company ABB. The project, called Mobile Machine Integration, enables all of the collected data to be available at one single control center, representing a significant step towards largescale integration of tunneling equipment into a process control environment. Mobile Machine Integration brings together ABB’s long experience of automation together with Atlas Copco’s cutting edge systems for capturing, transmitting and presenting


REMOTE MONITORING

machine data from mobile equipment. As a machine works and moves around underground, relevant information is collected by the on-board data system and transmitted wirelessly via WiFi access points to a local server. This data is then available to be displayed and analyzed in a variety of ways, as shown in Figure 1, on a standard computer screen and via a web interface, including all the vital parameters that are displayed on, for example, a drill rig’s display screen, including pressure flows, penetration rates, temperatures and more.

Adjusting parameters

To gather machine and production data is the main objective of monitoring. Another important function, however, is to be able to track all operations online so that the entire tunneling process can be controlled with as high efficiency as possible. As in all industrial production processes, unforeseen events may occur which is why it is an invaluable resource to be able to adjust parameters and set new priorities from one central location, with as little human intervention as possible. For optimized results, the Mobile Machine Integration system should be used with computerized equipment such as drill rigs, loaders and trucks equipped with Atlas Copco’s RCS technology. The RCS rigs are prepared for communication not only in terms of available data on the machine but also for standardized protocols such as IREDES (International Rock Excavation Data Exchange Standard). The technology can be applied to older machines too although this will mean that only a limited range of data will be made available and shared during operations.

Real-time data

Having access to real-time data regarding the status, location and activities of the equipment fleet allows for much greater control over the tunneling process. For example, a real-time alert indicating a delay in one process allows for the tunneling schedule to be altered immediately, thereby minimizing any flow-on effects. Similarly, real-time alerts regarding machine operational issues can be sent directly to the service department and acted upon immediately to prevent machine failures.

Figure 1: The Atlas Copco Certiq system is a base component of Mobile Machine Integration. It enables real time monitoring of production data, alarms and warnings, as well as the availability of drill rigs, loaders and trucks.

This enables potential mechanical failures to be predicted and averted, and idle machine time to be turned into productive time. Similarly, bottlenecks in the production process or ineffective work processes can also be identified and analyzed by the system. Mobile Machine Integration is designed for the harsh, underground environment where wireless infrastructure may well be less than perfect. It is also scalable, accessible from anywhere and can be easily integrated into other systems. At the same time, infrastructure such as fiber networks and antennas need to be installed in a good way to keep the system alive, using rugged components. With civil construction and tunneling in particular under increasing pressure to optimize processes and reduce costs, monitoring technology of this kind is an ideal beginning. In time, step-by-step developments will make it possible to observe and track all activities underground from one centralized control room. ◙


67


In short, having real-time information regarding the status of a tunneling fleet allows operators, supervisors and managers to make informed decisions on how to handle potential problems or disruptions before they occur, rather than after. The positive impact of real-time information on operational performance and cost is enormous. If the system indicates that a drill rig is reaching a critical point in any area, an alarm is raised. The supervisor can then alert the drill rig operator directly and, for example, issue an instruction that the rig must be delivered to the service workshop.

The control central gives tunnelers a bird's eye view of operations with real-time data for drilling, haulage, ventilation and other key tasks.

1

2

3

4

1. 2. 3. 4.

Portal access tunnel Access tunnel Main tunnel Service gallery

Figure 1: During the construction phase, the access tunnel makes it possible to advance the main tunnel from several headings. When the project is completed, it can be used as a service tunnel.

Tunnels – a prerequisite 1 Portal access tunnel 2 Access tunnel 3 Rail tunnel 4 Service gallery

for a connected society

The construction of tunnels for roads and rails continues to be a major contributor to the development of the modern society with advanced technology making it easier than ever to accomplish. If the wheel is the most important invention in the history of mankind, the tunnel is surely not far behind. In fact, it is often argued that it was the advent of the tunnel, which made it possible to travel through mountains, that is the key to all progress and development. In our modern times, few would deny the incredible contribution that has been made by the telephone, the Internet or mobile telephony in terms of connecting people around the globe. But nothing compares with the physical ability of

68

tunnels to carry huge numbers of people or goods from one place to another, often over long distances, and through seemingly inaccessible terrain. Furthermore, the role of the tunnel in the development of today’s society shows little sign of abating. Urbanization continues to grow exponentially across the globe, and with that the need to locate mass transit systems underground, along with increasing pressure on infrastructure networks, both domestic and cross-border.


ROAD AND RAIL TUNNELS

How it all began

The earliest recorded tunnels, such as the one beneath the River Euphrates in Iraq that dates from about 2 200 BC, were built for pedestrians. They were generally short and just large enough for one adult male to walk through. In more recent history, in the latter part of the 1700s and early 1800s, tunnels were built as conduits for canals, enabling barges loaded with goods to pass between towns and cities through difficult terrain. However, in October of 1829, everything changed when thousands of people descended on the tiny English village of Rainhill in the UK, halfway between Liverpool and Manchester, to see five steam locomotives compete against each other over a distance of 56 km (35 miles). Stevenson’s “Rocket” famously won the contest, achieving a top speed of 48 km/h (30 mph), hauling 13 tonnes. Stevenson picked up a check for GBP 500 as well as a contract to start building locomotives for the Liverpool and Manchester Railway – and the rest is history. What’s significant about this milestone is that prior to the advent of the railways most people in the UK lived and died within a radius of just 15 miles of their home. Within 20 years of the Rainhill Trials, however, a network of railways had been developed that made it possible for every working man to afford to travel. The impact was felt across the world. Continents opened up and the industrial revolution gained huge momentum in the 19th century. By 1850, there were no less than 8 000 km of railway in operation in the UK alone (see Figure 10 p.76). But there was a problem. Railway tracks could only be laid on very gentle slopes and bridges and tunnels had to be built to carry the tracks across valleys and through hillsides. However, bridges and tunnels were expensive, which is why most older railroad lines have quite narrow curves and many bends.

Two thirds of existing rail networks were built before the 20th century. The majority of these have been upgraded since the 1960s.

To create rail connections between central and southern Europe, it was necessary to build tunnels through the Alps. Many of these were built at high altitudes and the trains had to negotiate many bends on the climb up to the tunnel entrances. Figure 11 (p. 77) shows the construction date and location of some of the biggest early Alpine tunnels.

Construction began in 1973, and since it was designed for fast passenger trains as well as for express freight trains, its maximum incline is a mere 1.25%. Combined with the hilly terrain, however, it runs through 61 tunnels and over 10 large bridges. Of the total length of 327 km, 120 km are through tunnels. The line was opened fully in 1991 and the standard speed is 250 km/h (155 mph), although 280 km/h is permitted if a train is running late.

Road tunnels

Obviously, road tunnels used by pedestrians and horse-drawn carriages have a much longer history than rail tunnels. The number of early road tunnels far exceed those used for railways, but it was not until road transport using automobiles soared after World War II that the demand for higher road standards began to increase. To meet those demands, major


69

Underground construction

By the end of the 19th century, more than two-thirds of the currently existing railway lines had been built. This means that the majority of the lines being used as late as the 1960s did not allow for high speed trains due to the alignment standard for grades and curves applied at that time. Since then, many stretches have certainly been upgraded, both without going underground but also into tunnels. As the roads improved and cars and trucks started to compete with the railways and to a certain extent, air transport, it became clear that a major upgrade of the rail network was a must. The alternative was that rail transport would continue to decline and eventually die out.

A good example of an upgraded railway is the new Hanover – Würzburg line in Germany. This was the first of several highspeed railway lines to be upgraded for Inter-City Express trains and, at 327 km long, it is also the longest railway line in the country.


Figure 2: Underground road and rail tunnels are essential in cities with high population density, where metro lines are also integral to the mass-transit system.

improvements were made from the 1970s and onwards, and in many locations throughout the industrialized world, roads went underground. These tunnels were built in urban areas to ease traffic jams – The Periferic around the city of Paris is a good example – and in rural areas with intense traffic to overcome major shifts in altitude, such as the Eisenhower Tunnels in the Rocky Mountains in North America. In addition, road tunnels were built wherever it was cheaper to go underground than to build on the surface, such as the second Tomei highway in Japan between Tokyo and Nagoya. The decisions that determine the upgrade or creation of new traffic routes, are largely taken by national and local government authorities and often involve extremely large investments. As a rule, decisions to build new routes only become politically viable when the existing traffic situation has reached unbearable proportions for the citizen. There are models for estimating the advantages of creating new traffic routes, where time savings for the user and added value for communities, with respect to an improved environment, are two of the biggest plus points. To facilitate this decision-making process, some roads, tunnels and bridges are

70

financed by toll payment systems. Other financial solutions used to make major traffic installations come to fruition are the so-called Build, Operate, Transfer projects (BOT). In this case, venture capital companies and contractors form joint ventures to provide the necessary finance and then take the income from the toll over a defined number of years, after which they hand it over to the local government administration. A typical example of a BOT project is the express rail connection between the city of Stockholm, the Swedish capital, and its international airport, Arlanda. This is a line that includes some major tunnels as well as an underground station at the airport terminal.

The underground option

One way of overcoming traffic jams is to give citizens the option of a fast public transport system underground. Very few cities with a population of less than half a million are able to enjoy the advantages of a metro, and there are many cities with a population of over one million that still do not have one. This means that the first metro will inevitably have to be built in congested areas with all the difficulties and costs this involves. A case in point is the New Dehli metro where some of the central parts have now been completed. When the time comes to expand into the suburbs, the additional metro



Because of its fjords and mountainous terrain, Norway has over 1 000 road tunnels totalling more than 800 km. The tunnel shown above, Glaskartunnelen, is 592 m long.

lines will simply be natural extensions of the existing infrastructure. Another important issue is to consider where road or rail tunnels should be located. The majority of rail tunnels are located in urban areas where metro lines also constitute a large part of the mass transit system (see Figure 2). Regular rail tunnels and stations, not only those for metro lines, have become viable solutions over the past few decades. One example is the new lower level of New York’s Grand Central Station, with the eastern access crossing the East River underground.Another example is a new, extremely large underground railway station complex now being constructed in Stuttgart, Germany. The new railway line that runs between Copenhagen, Denmark, and Malmö, Sweden, is also, in large part, placed underground. Metro lines, on the other hand, are naturally located in the most densely populated areas.Road tunnels have not only becom an important part of the transportation networks within cities. Many of the ringroads that circumvent traffic around the cities are also, to a large extent, placed in tunnels.

The Plabutsch tunnel in Graz, Austria, is an excellent example of this. It was during the 1970s that it became obvious that traffic could no longer be permitted to run through the 1 000 year old city. But the question was where to locate the new highway. After a long and protracted debate, it was decided to place as much as 10 km of the new road in a tunnel through a cliff that borders on the suburbs, west of the city. An alternative to this plan was to place the highway even further westward on the other side of the Plabutsch mountains. There was a 15-year gap between the construction of the first and the second tunnel. To some extent, this confirms the belief that new roads and tunnels are normally only built when the traffic situation becomes unbearable.

Different methods

The mechanical breaking of rock by means of a Tunnel Boring Machine (TBM) is one method of building tunnels. Here, the full tunnel section is excavated in one operation. The machine, or TBM, is designed to tackle the prevailing rock conditions which in most cases means that it is best suited for excavation in one type of ground. Without


71


In addition, there are several examples where major arteries through cities have been rerouted underground. The relatively new Boston city tunnel is a good example. In addition, it has also become increasingly common to reroute traffic that

previously ran through the city centers to the city outskirts via tunnels.


1

equal conditions. This means that the TBM method is preferable for small-size tunnels due to its high speed. Long tunnels are also suited for mechanical excavation as they offer more tunnel meters on which the depreciation of TBM gear can be distributed. That said, the opposite is true for the drill and blast tunneling method. Road and rail tunnels must be considered as large tunnels with cross-sections that are seldom smaller than 60 m2, with the exception of metro tunnels that may be as small as 25 m 2. On the other hand, even metros must have closely located stations that require the cross-sections to be enlarged. In those cases, it is common practice to excavate the running lines by TBM and develop the wider sections at the stations by conventional drill and blast.

2

1

2

2

In weak ground formations and in city centers the station may be excavated by the road header technique in order to eliminate disturbance from blasting operations. Choosing between these two excavation methods is far from easy, and it is not uncommon to employ both techniques at the same construction site. Conventional excavation by drill and blast is preferred by many due to its flexibility in dealing with the variations in both tunnel cross sections and ground conditions. However, it is more demanding in terms of skills as the technique of mechanical excavation is easier to learn. For more information on TBM vs. Drill and Blast, see chapter "Choice of methods" p. 174.

Excavating the face

Figure 3 and 4: To achieve a faster advance rate in wide openings, top heading excavation and benching can be conducted simultaneously. In short and large tunnels, the top heading is excavated first.

going deeply into the technique of excavation by TBM, it is important to understand the circumstances in which the TBM method is preferred. The excavating tools on a hard rock TBM are the so-called disc cutters that create a circular cutting path on the tunnel face. Each disc has its own path and the paths are concentric. The cutters are limited with respect to the load they can take and the speed at which they can roll. This means that the outermost cutter located on the rotating head determines the machine’s rpm. The consequence of this is that the larger the diameter, the lower the rpm. The advance rate of the heading is, therefore, dependent on how deep the cutters can penetrate the rock with each revolution and the number of revolutions per minute. In principle, a 4 m diameter machine will advance twice as fast as an 8 m diameter machine when operating in

72

Excavation of full section or just partial sections is an issue for all large tunnel excavations. Today, drill rig suppliers offer rigs that can cover cross sections up to 200 m 2 in one setup at the face. So limitations on excavated face area are rarely a problem for the tunnel builder. The reason for splitting a large face might be the rock quality. A large face may not be able to stand up long enough to allow for the required rock support to be installed. In single-track tunnels, being some 8.5 to 9 m high and 6.5 to 7.5 m wide, full section excavations can normally be achieved even under poor rock conditions. One example of this is the Lötschberg base tunnel in Switzerland, which is some 40 km long and was excavated by both TBM and the drill and blast method. The latter was preferred by the client in sections with poorer ground conditions, which, incidentally, dominated this project. The rock conditions along the tunnel route were classified into five groups, each with a defined amount of rock support to be installed and defined lengths of the rounds. In none of the support or excavation classes were the single-track tunnels given a split section. The length of the rounds were set to make it possible to install the required rock support in due time to avoid the ground surrounding the opening from loosening. For blasthole and



bolthole drilling, three-boom drill rigs were used, assisted by two-boom rigs operating behind the tunnel face. By maintaining the same invert level throughout the excavated tunnels, a mucking system using continuous conveyors turned out to be an attractive hauling solution. In wider underground openings, such as road tunnels where simultaneous excavation on two levels is possible, this excavation concept is applied on longer tunnels since, in many cases, it gives a faster advance rate when considering the whole tunnel section. The principles are shown in Figure 3. In shorter and larger tunnels, it is seldom worthwhile to start the process of simultaneous top heading excavation and benching. In these cases, the top heading is excavated all the way through, as shown in Figure 4, followed by the excavation of the bench.

1

2

In wide sections, 15 m or more, the top heading itself is split into two or three headings. The reason for this may be a fear of instability when opening up a very large face in ground conditions that are characterized as weak rock. By splitting the face, rock support can be installed without jeopardizing the stability. Splitting of the top heading face in large underground openings with good rock conditions may also be the case. Multiple faces offer a better opportunity to utilize the equipment that is allocated for the tunneling work, and a better utilization gives higher flow of rock out of the tunnel or cavern. Cavern excavation is a form of tunneling but with essentially larger dimensions. Here, the tunnel width is in the range of 20 m and the principles for multiple heading excavation can be seen in Figure 5. They should be at least a couple of rounds. For a better understanding of what large underground openings may require when the rock material is weak, or has a swelling characteristic, the excavation sequence for a three-lane road is shown in Figure 6. When deciding on which type of excavation approach to take, the details of the excavation process have to be established. The process itself holds a number of sequential operations and these are shown in the sequential diagram shown in Figure 7. In this case, eight activities are involved, although the number of activities may vary depending on ground conditions and the demands of the design. For example, the mucking may have to be carried out in two steps in order to apply the sprayed concrete support as soon as possible to secure the stability of the face area. Step one in mucking is to give access to the heading for the concrete spraying equipment. In order to achieve this, roughly onethird of the muck has to be shifted.

3

1

4

3

5

4 5

Figure 5 and 6: The principle of multi-heading excavation for large underground openings, typically 20 m wide or more. Bottom illustration shows the excavation sequence for a three-lane road in weak or swelling rock.

Overbreak and support

The process of minimizing the overbreak and support starts with the drilling of the blastholes. The hole diameters are normally in the range 43 to 52 mm, where probably 45 mm is the most commonly used. There is a trend towards larger hole diameters as they offer the opportunity to go for larger diameter drill rods that are stiffer. Stiffer rods tend to give less hole deviation, which is very important for the economy of the excavation. In civil construction for road and rail tunnels, it is of great importance to stick to the lines and grades given in the design documents. Overbreak means excavation beyond the stipulated contour. The majority of rail and road tunnels around the world are given a two-layer support with a primary layer applied in the face area which is good


73


Another example is that pre-grouting may be required for sealing the ground and that drilling for grout holes and grouting will have to be carried out, although normally only for every third round.

2


rigs for civil tunneling are capable of locating the blasthole collaring point with an absolute accuracy of less than 10 cm. This is achieved by having the drill rig position established with an accuracy of 1 cm.

www.atlascopco.com

EC

EC

Bolting

Drilling and Surveying

Concrete spraying

Charging

The position of the rig and its angle to the tunnel axis are registered by use of total station readings utilizing fixed points back in the tunnel and fixed points on the rig itself. For the actual face to be drilled, the valid cross section and drill plan are stored in the rig’s onboard computer. This means that the rig knows exactly where to collar the hole as well as the drilling direction. In addition, the rig’s boom arms and joints are programmed to follow the directives from the computer. However, it is not possible to be more exact than the given figure due to inaccuracies mainly in the mechanical systems.

Scaling

Blasting

Mucking

Ventilation

Figure 7: The sequential operations performed at the face in tunneling.

enough to stabilize the rock at least during construction and, in many cases, much longer.The secondary support is often an in situ concrete lining and the two layers are meant to have a service life of 100 years, sometimes more. This lining has a very accurately defined inner contour. The space between the rock surface and the inner contour of the lining has to be backfilled with sprayed concrete and concrete. This means that all overbreak has to be replaced by concrete or sprayed concrete, which is very costly for the tunnel builder. To spend major efforts on hole-drilling accuracy of the contour holes is something that usually pays off. Stiff drill rods which give only a minor hole deviation, are a low cost way of reducing the amount of overbreak. Accurate contour holes are not only economical for the builder, but also have significance for the rest of the holes in the round. An accurately drilled cut (start of the blasting) means, in most cases, a good pull of the round. A good pull gives an excavated length that is 92% of the drilled length or more. The majority of the holes are normally located in the cut and along the contour. The latter are closely placed, allowing the amount of explosives used to be considerably reduced, and this is meant to give a nice, straight cut of the rock between the holes and, consequently, limited overbreak. Accurate hole drilling also means that the holes are being positioned in the right place along the hole length. Modern drill

74

To quantify the advantage of investing in a technically advanced drill rig with the Rig Control System (RCS), in comparison with an older type, it can be said that the additional investment is paid back after less than 2 km of tunnel with a cross section of 70 m 2. This is due to the savings on sprayed concrete that can be realized when using a price of USD 150/m3 and USD 300/m3. The blasting agent is normally of a bulk type since it is easier to charge as hoses are used for pumping the explosives into the holes. The cheapest type is ANFO, but more and more users are going over to emulsions as these can cope with wet holes in a far better way. A more advanced way of using the emulsion is to apply the string loading technique. This technology offers the possibility to partially fill the holes. This means that one type of explosives can be used in all holes and the explosive strings are given weight variations adapted to the position of the holes. The periphery holes are normally given the lowest weight/m hole. For more information see chapter charging and blasting, p. 130.

Mucking out

Mucking of the rounds is almost always conducted by use of a regular wheel loader. In road tunnels holding two lanes and curbs, the width is in the range of 9 to 11 m. This gives good opportunities for loading of trucks right up at the face, using the standard way of tipping the buckets into the truck bed and fairly big loaders. In rail tunnels, the situation is somewhat different. The width of the single-track tunnels will not allow larger wheel loaders to dump the bucket into trucks in the conventional way (pin on). One option is then to arrange loading bays at defined distances and perform the loading, as shown in Figure 8, which is a common way to do it in smaller tunnels. Another option that has become attractive is to equip the loader with a bucket that can be tipped sideways (see Figure 9).



This offers the opportunity to load the trucks right up at the face. At longer haulage distances, which might be the case in rail tunnels, the use of a conveyor might be an attractive alternative. For more information,chapter "Loading and haulage", p.158. To be able to send the blasted muck on the conveyor it has to be crushed into smaller fractions. A mobile crusher, therefore, has to follow the advance of the tunnel heading at a distance of 50 to 100 m. The crusher is fed by side-dumping wheel loaders, but other alternatives are also viable such as continuous muckers, e.g Häggloader.

<300 m

Scaling

Scaling is normally the first action to secure roof walls and the faces at the heading. In many cases, it is performed before the mucking. The technique used to perform the scaling varies considerably. The variation depends on geological conditions, which is easy to understand. There are also regional differences in the applied technique. Scaling in parts of Asia may be different from how it is done in Scandinavia, even though the ground conditions may be similar. Manual scaling using a crowbar is still very frequently used worldwide. Modern civil engineering tunneling generally involves mechanized scaling, but the type of mechanical tool used varies. In hard igneous and highly metamorphic rock, the hydraulic breaker is frequently used, while in lowstrength, sedimentary rock scaling is often not performed at all. In the latter case, only cleaning is done using concrete spraying equipment and water mixed with air that is sprayed onto the surface, bringing down the loose pieces of rock. A hardhitting hydraulic breaker, would, in this case, cause more harm than good by tearing down loose blocks and triggering a minor or even a large cave-in, in the heading area. Ripping by use of a mechanically activated steel stud is also practiced in some parts of the world.

<300 m

Figure 8: Loading in small tunnels with narrow cornering requires loading bays to be excavated at calculated distances.

However, this technique requires a manual checkup by use of a regular crowbar. Rock support goes hand in hand with rock excavation. These are two inseparable technologies. It can also be said that breaking and mucking of rock are the two major constituents in rock excavation.

Figure 9: Equipping loaders with buckets that can be tipped sideways is an increasingly favored option.

The terms primary and secondary support are also frequently used in this context and they overlap the other definitions.


75


In civil tunnel construction, there is a distinction between temporary and final support and also primary and secondary support. Temporary support is installed just at the tunnel face as a first step to secure the heading area from falling rock, which simply makes it safe for people working there. It may have a short service life but may also constitute a part of the final rock support..


Railway net in Europe 1850

Figure 10: The developed status of the European railway network in 1850.

However, primary support sometimes means rock support that over a long timespan will give a stable, underground opening, and the secondary lining is insurance that in case something fails in the primary rock support, the secondary support will be there to prevent a disaster. A full concrete lining is often called secondary support or secondary lining. In conventional tunneling, this secondary lining is cast in situ and is carried out after the completion of the excavation of short tunnels, but for longer ones excavation and lining have a timewise partial overlap.

Achieving stability

There are two common means of securing the stability of roof, walls and face at the tunnel heading – bolting and concrete spraying. They can be used individually, but it is more common in civil tunnel construction that they are installed in parallel and interact, which is an economical solution to the issue of stability. “Bolting” means that steel bars are installed in drilled holes by use of a bonding agent such as a cement grout or a resin. The latter is a mixture of two components, a matrix and a hardener. The advantage of the latter is that full bonding strength is achieved within a minute or two, while cement bonding needs days before reasonable loads can be taken, and full bearing capacity needs weeks.

76

However, there are other possible solutions to achieve fast operating cement-grouted bolts and that is by using mechanical anchoring at the bottom of the hole and a washer and nut at the other end. Using this method, about 30% of the final loadbearing capacity can be achieved and the bolts are normally given a pretension of that magnitude. The grouting of the bolt can then be made well behind the face. The grouting serves two purposes, firstly to transmit the load from the rock to the bolt and vice versa, and secondly to act as protection against corrosion. The first statement needs a short explanation. The bolt is normally oriented perpendicular to the rock surface and the bolt that is anchored in the inner part reduces the possibilities for the rock surface to move inwards to central parts of the tunnel opening. That means there is an on-loading reach of the bolt closer to the surfaces and off-loading reach closer to the bottom. The load transfer is made via adhesion for the grouted bolts. There are other types of bolts where load transfer is done by friction. A mechanical bolt anchor is one type, and another is a bolt in the shape of a pipe with a longitudinal slot. The pipe is forced into the hole, which has a smaller diameter than the pipe, and the width of the slot is reduced by the



AUSTRIA

GERMANY

Salzburg

FRANCE Feldkirch Berne

SWITZERLAND

5

Langen S:t Anton Kandersteg

4 Goppenstein

3

Innsbruck

Böckstein

6

Mallnitz

Göschenen Airolo

Brig Iselle

2

ITALY

Chambéry Modane

1

EUROPE

Milano

Turin Bardonecchia

1 Fréjus railway tunnel, 13.7 km, 1857 – 1871 2 Simplon railway tunnel, 19.7 km, 1898 – 1906 3 S:t Gotthard railway tunnel, 15.0 km, 1871 – 1882 4 Lötchberg railway tunnel, 14.6 km, 1906 – 1912 5 Arlberg railway tunnel, 10.6 km, 1880 – 1884 6 Tauern railway tunnel, 8.4 km, 1901 – 1906

Figure 11: To create rail connections between central and southern Europe, it was necessary to build tunnels through the Alps. Many of these were built at high altitudes and the trains had to negotiate many bends on the climb up to the tunnel entrances.

pressure from the bolt hole wall. This pressure can mobilize friction forces that will reduce the movements in the rock mass. Another bolt of that type is the Swellex bolt, which is also a tube bolt that, when inserted in the bolt hole, is given a plastic deformation making it form to the hole but also exert a remaining pressure against the wall, even when the internal pressure is released. The internal pressure is created by water having a water pillar of 3 km (30 MPa). The advantage of these mechanical bolts is the fast installation and immediate support capacity. The disadvantage is that they are not corrosion protected. Sprayed concrete is a form of concrete that is applied to the rock surface and sticks to it by adhesion. In general, thin layers are applied and they are rarely more than 5 cm in thickness. The stabilizing effect is achieved by the fact that the blocks of rock mass around the tunnel opening are being linked to each other by the adhesion capacity and load transferring ability of the thin concrete layer.

Two types of sprayed concrete

There are two types of sprayed concrete – dry-mix and wetmix. The dry type is the oldest and has been in use for more than 60 years. In fact, dry mix cases far older than this can be found, but their use was very limited. Wet mix was introduced more than 20 years later and is today the dominating application technique. There are reasons for that, such as offering higher spraying capacity, a healthier working environment and less spillage, also called rebound, to mention just a few. The wet mix is delivered to the concrete spraying equipment by regular concrete trucks which means that water has been added. The concrete is pumped up to the spraying nozzle by regular concrete spraying pumps. At the nozzle, the pumped concrete is accelerated by compressed air brought into the nozzle by a separate air hose. In the dry mix method, aggregate and cement are mixed in a dry state and can stay like that as long as the water content in the aggregate is very low.


77


The sprayed concrete mix differs somewhat from that of regular concrete used in the lining of tunnels. The aggregate has a maximum size of 8 mm and the cement content is considerably higher. In most cases, there are additives that accelerate

the hardening process, which means that the applied concrete sets within minutes. For more information, see chapter "Rock reinforcement", p.150.


To secure the stability of tunnels, bolting and concrete spraying are common reinforcement techniques. Pictured here is the MEYCO Potenza concrete spraying mobile.

This means that the ready-mixed material can be stored in standby mode in the proximity of the tunnel heading for hours and used on very short notice. The dry mix is transported by compressed air in a wide hose up to the spraying nozzle where water is added. The dry mix is fed into the hose by a concrete spraying gun, which has a revolving chamber like a shotgun, so the material is sent in small batches with a frequency of around 1 Hertz. To improve the tensile strength of the sprayed concrete, it can be reinforced like regular concrete. Sprayed concrete fibers have become very popular and are of either steel or plastic. Not just the tensile strength is drastically improved but also the ductility, which means that the sprayed concrete can take larger deformations. There are many other types of rock support being used, such as steel arches, lattice girders, self-drilled rock bolts, and spiles ahead of the tunnel face, as well as stabilizing the tunnel face by installing long, glassfiber anchors which are cut as the face advances.

Concrete lining

Most rail and road tunnels are given a secondary lining as previously mentioned. This lining is almost always of a concrete type and is rarely reinforced, except for some meters in the portal areas. The concrete is cast in situ, and the casting is normally made in two steps, first the invert and then the arch. Specifically designed shutters are engaged. They are collapsible and are therefore easy to move and erect in a new position.

Sealing the ground

In some regions, typically in Scandinavia, which has a special geological situation, a lowering of the ground water cannot be tolerated. Therefore it has to be assured that the leakage of

78

water into the tunnel must not exceed predetermined levels. The levels are usually defined as “liter/minute and 100 m of tunnel”. The span for the level is in the range of 0.5 to 10 and very frequent. In urban areas the figure is around 2 and 3. This means that great effort has to be made on sealing the ground, and the only viable way of attacking the problem is to seal the ground by use of pre-grouting. To seal when the tunnel heading is already in the water yielding zone is very difficult, and in many cases it is impossible to achieve the targeted limits of water inflow. Pre-grouting technology has been developed over the last four decades and mainly based on cement grouting due to environmental reasons. For more information, see chapter "Grouting" on p. 164. Summing up in a very simple way, it can be said that a number of holes are being drilled with collaring close to the tunnel periphery and ending some 3-4 m outside the periphery line of the tunnel. It has to be emphasized that the holes along the invert are just as important. The length of the holes are normally 20 to 25 m, and when continuous pre-grouting is required, the sets of holes overlap by 4 to 5 m. The grouting work itself is not just the pumping of any water cement mixture, but a well-established procedure based on pressure, flow, water cement ratio and response from the rock itself. In order to achieve the targeted sealing effect, the grouting process is carefully monitored, with data stored and evaluated using computer software. For larger work sites, mobile grouting units are used. Checking the result is an important aspect of the process. On some sites, the MWD (Measure While Drilling) technique is applied to obtain an initial concept for how to carry out the sealing over a defined tunnel section. ◙


ROAD AND RAILWAY

79



1

9 2

3 4 5 6 1 Intake 2 Headrace tunnel 3 Surge chamber 4 Penstock 5 Powerhouse 6 Transformer hall 7 Tailrace tunnel 8 Outlet 9 Intermediate adits

7 8

Figure 1: A typical 3D overview of a modern hydroelectric power station with key construction elements placed underground.

Hydropower –

the renewable energy source Hydroelectric power supplies more than 1 billion people with renewable energy, and the market is growing steadily. As new hydropower projects get underway, more and more of their construction elements are being placed underground. Hydroelectric power has become a competitive source of renewable energy due to its relative low cost advantage. As a result, the number of hydropower plant being built around the world has grown steadily over the past years. Although hydroelectric power is regarded as being a renewable energy source, the building of dams and reservoirs and

80

other essential facilities can have a negative impact on local ecosystems, rivers and wildlife. It is, therefore, of utmost importance that the best possible practices are adopted in dam construction and in the installation of tunnels that regulate the water flow to powerhouse generators. Topography, the study of the Earth’s surface, and environmental considerations are two key aspects that influence the layout and design of


HYDROELECTRIC POWER PLANTS

An underground powerhouse showing six generators placed under the floor with only Kaplan heads (blue) visible.

hydropower plants (HPP) and will dictate the choice of dam site, tunnels and canal lengths. Another key factor is the costs associated with each individual design solution.

Hydropower on the rise

Hydroelectric power generation is by far the largest renewable source of energy today. China, Brazil, the United States, Canada and Russia account for 52% of the world’s installed hydropower capacity. Furthermore, there are currently three hydropower plants that have a larger than 10GW installed capacity: the Three Gorges Dam in China, Itaipu Hydroelectricity Power Plant in Brazil, and Guri Dam in Venezuela.

Basic facilities

Each project is unique, yet a current trend is for more and more HPP to utilize underground space for the installation of basic construction elements. Environmental preservation has been a driving force for this development, which has led to vastly improved methods for minimizing the surface footprint of hydropower plants. Other reasons may include security because facilities spread out over large geographic areas entail higher security risks, as well as economic aspects because underground structures may be more cost effective. The planning of a hydropower facility usually begins upstream by looking at the potential for dam construction, typically at a river cross section as shown in Figure 1, which gives a 3D view of a modern hydroelectric power station. Dams can vary greatly in design and often constitute the


81


A principal requirement for hydropower is a natural landscape that is characterized by altitude differences between lakes and rivers. And in parts of the world where conditions are favorable, a considerable growth of HPP projects is being witnessed. Projects in Asia and parts of South America are on the rise, as well as Africa which is widely considered to have huge potential for development. Time is a crucial factor

in all construction but particularly in hydropower plants. As soon as a hydropower plant is completed and the dam area is filled, the facility can come on-stream and begin to generate income for the owner.


1

4

2

3

1 Intake 2 Penstock 3 Turbine 4 Generator

Figure 2: Principle drawing of a hydroelectric power station that does not feature underground structures.

greatest1 and most time-consuming construction element. Intake Below follows a description of the underground construc2 Penstock tion elements. They are presented in order, from intake at 3 Turbine 4 Generator the upstream end to the outlet at the downstream end (see Figure 1).

Grouting galleries

In order to reduce the time spent on preparation work for the dam foundations, which involves extensive grouting, a tunnel is often built directly below the dam axis. This tunnel is known as a grouting gallery and enables grouting work to be conducted in parallel with the construction of the dam itself. Grouting galleries are typically of moderate size, 3–4 m in diameter, horseshoe shaped and concrete lined. Conventional drill and blast excavation is normally the applied method and the galleries extend across the full length of the dam. When completed, they provide just enough space for grout-hole drilling equipment, which often includes core drilling rigs. The main advantage of using core drilling instead of ITH drilling is that in the former drill cuttings will not block open joints and hamper the penetration of the grouting agent.

82

Desilting basins

The next step, following the path of the water, is the construction of desilting basins, but this may vary depending on the requirements for each project. It is often the case that rivers carry with them a lot of suspended mud and silt particles, which, in turn, cause excessive wear to the mechanical parts of power generators. The solution to this problem, when there is a shortage of open air space, is to create long underground caverns that enable the suspended particles to settle. These caverns, also referred to as chambers or forebays, are normally located in river valleys where the water influx is brought to a slower pace. Settled material needs to be flushed out intermittently, which means that at least two caverns need to be constructed. Dimensions can vary greatly, but a cross section of 100 m 2 is not unusual. The drill and blast method is employed and the top heading is excavated in a traditional way. The benching is given a different excavation approach due to a design with sloping walls. These are needed to facilitate the accumulation of sediments for later flushing out with water. A considerable number of concrete structures are needed to shape the sedimentation caverns. Here, concrete is poured



1

2

3 4 5

1 Intake 2 Penstock 3 Powerhouse 4 Generator 5 Turbine

Figure 3: A hydroelectric powerstation with no underground headrace structures but an underground powerhouse. It has a long vertical penstock.

against blasted rock surfaces which means that smooth blasting is encouraged in order to keep the consumption of concrete to acceptable levels. Rock excavation for this application is often an extensive undertaking in terms of volume and requires drilling and mucking units. However, desilting chambers are seldom critical in the construction cycle for finalizing an HPP as they can be initiated independently from the construction of other basic facilities.

Headrace tunnels

In the majority of HPP projects, the headrace tunnels are not pressurized but are, instead what is called “free float tunnels”. This means that if they are given an even decline it is possible to have a small free water surface in the crown of the tunnel. Headrace tunnels are normally drained and that means that ground water lying in the surrounding rock is free to enter the tunnel. The purpose of this is to avoid an outer pressure on the lining.

Surge chamber

The mass of water flowing in the headrace tunnel holds a large quantity of kinetic energy. The magnitude is dictated by the volume and its velocity. To be able to close a power


83


Following the path of the water, the headrace tunnel is the next construction element for HPP. Its purpose is to transport water from the desilting basins, or forebays, to the surge shaft. These tunnels may be constructed for pressure flow or gravity flow, although the latter function is more commonly applied. Dimensions vary greatly between each project, but headrace tunnels as long as 10 km are by no means unusual. It is even possible to encounter headrace tunnels that are 20 km long. The cross section can be anywhere from 10 m2 and upwards. Sections smaller than 8 m 2 , however, are rare because the available space becomes too confined for

tunneling equipment and personnel. Some power stations are built without headrace tunnels, as shown in Figures 2 and 3. So what dictates the size of the tunnel cross section? The answer is the flow of water where the velocity will be modified to keep head losses low. For blasted tunnels that have been given only a sprayed concrete lining, or no lining at all, the velocity of the water is normally in the range of 1 m/s. For concrete-lined tunnels, the velocity can be doubled or even increased slightly more.


also compromising the stability of the shaft. To avert this risk, most penstocks today are constructed with a concrete lining, or a concrete and steel lining, in order to secure the water column. The dimension of the penstock is considerably smaller than the headrace tunnel and excavation is normally carried out from the bottom and up. At the bottom end of the penstock, there may be bifurcation to distribute the water to two or more turbines.

Securing the powerhouse

The powerhouse is a cavern-like structure of considerable width and height where the turbines and generators are located. Typically, the size of the powerhouse depends on the number of power units to be installed inside the structure. To ensure safe, long-term operation of the turbines, considerable efforts should be spent on securing the cavern roof from falling rock, as even smaller pieces of rock may cause damage due to the vertical height. Should a generator be damaged, the costs are allocated to the loss of power generation and, for this reason, the roofs are often given a concrete lining. In some cases, depending on geological conditions, the entire powerhouse may be lined with concrete for increased safety.

Tailrace tunnels

Large drill rigs, such as this three-boom rig, are typically required to excavate the powerhouse, transformer hall and diversion tunnel.

station over a short time interval (minutes), the kinetic energy must be taken care of. This is done by adding a surge chamber into which water from the headrace tunnel is diverted and the kinetic energy is turned into potential energy. In HPP projects where the headrace tunnel is long, the surge shaft excavations are a major undertaking due to both the height and diameter. The shafts are normally given a round shape and are excavated from top down.

Penstock design

The water is then brought into a vertical or declined shaft that is called a pressure shaft or, more commonly, a “penstock”. The penstock (see Figure 3) is generally given a far smaller section than the headrace tunnel, and consequently the velocity of the waterflow is increased significantly. Water pressure is a delicate aspect of HPP design. Depending on the geology and rock stresses surrounding the facilities, water pressure may cause fractures in the host rock environment. These cracks can potentially lead to water losses while

84

When the water has left the turbines it is discharged into a tailrace tunnel to lead the water away from the power station. This tunnel is of a similar size as the headrace tunnel, or slightly larger. Its length depends entirely on the topography of the site and other design considerations and, consequently, will vary. As on the intake side of the HPP, a surge chamber may be required to mitigate pressure variations that occur due to the rapid velocity changes in the water flow. The surge chamber is often a large dimension vertical shaft that provides additional storage space. As for the headrace tunnels, geological conditions and groundwater levels are key considerations for engineering the tailrace tunnel, because external load is one factor that will influence the choice of concrete lining and whether this should be used at all.

Diversion tunnels

Another major temporary structure is the channeling of water through the dam area while building the dam. This is mostly done by use of a diversion tunnel. It is given a far larger cross section than the headrace tunnel as it has to be able to cope with the peak flow levels of the river to avoid flooding the dam-site. It is not unusual that more than one diversion tunnel is required. The length depends on the size of the dam and the



prevailing ground conditions but they are normally less than 1 km. A typical practice if ground conditions are poor is that a number of smaller diversion tunnels are constructed instead of one large tunnel, which minimizes the risk for stability problems when excavating.


Most underground excavation today is performed using two main methods, drill and blast or TBM (Tunnel Boring Machine). From a general point of view, tunnels with short, wide, irregular cross sections as well as tunnels with short curves and complex geology are excavated with the drill and blast method. Long tunnels of moderate size where the cross section is largely unchanged are often excavated by TBM. When it comes to HPP projects, headrace tunnels are typically evaluated for both excavation methods, and this may also apply to tailrace tunnels if they are especially long. Almost all other HPP rock excavation work is carried out using the drill and blast method. Due to the variable cross sections and lengths of the tunnels built for hydroelectric power plants, a range of equipment needs to be employed at the site to be able to effectively perform the excavations. The largest openings are normally made for the powerhouse, the transformer hall and the diversion tunnels. These tasks require large drill rigs, loaders and trucks to meet the given time schedule. For drilling, this means that three-boom rigs are often employed to give a good coverage and a short drilling time. In the powerhouse, the excavation has to be performed in stages, starting with the crown area. Here, large three-boom rigs are also viable and the wide opening gives the opportunity to operate with more than one rig at the face. As the powerhouse is usually given a fairly large height, it is necessary to create accesses at different levels, meaning that the area surrounding the powerhouse will typically feature a large amount of tunnels (see Figure 1). In addition to the underground structures for the waterways, there are a number of other underground openings required: access tunnels to the various construction parts, rooms for opening and closing of valves, shafts for power cables that bring the harnessed electricity from the underground generators to the surface, and so forth.

Drill and blast vs. TBM

geological conditions favors drill and blast operations. However, it must be emphasized that each project is unique, and choosing between the two methods must be based on properly made investigations. The drill and blast method is slower but flexible, and the slower advance can be compensated by creating more headings by use of intermediate adits. Although most hydroelectric power projects will choose one or the other excavation method, there are examples of HPP construction where both methods have been utilized, such as the Meraker hydropower plant in Norway. It features a number of both headrace and trailrace tunnels that are all of moderate size. The geological conditions were favorable for mechanical TBM excavation because the ground was stable and allowed for high penetration. In this case, the weekly advance at the TBM heading was three times the drill and blast excavation. This means that three conventional headings would have made the same progress as one TBM. Considering the large investment a TBM solution requires, it is understandable that the contractors put considerable efforts into calculating each method.


85


In HPP projects where the waterways are long, there is always a question whether to go for drill and blast excavation or to use the TBM method. The choice is based on a number of parameters, including the dimensions of the tunnels, diameters and lengths, how easily the rock is broken by the TBM (abrasivity strength) and how variable the geological conditions are. To simplify, it can be said that long and small diameter waterways favor TBM, while high strength abrasive rock and variable

The Atlas Copco Häggloader provides a continuous loading system. It is ideal for hydropower tunnels from 8 m 2 in size.


Th 1 2 3 4 5 6 7

Figure 4: Powerhouse excavation using the bench drilling method.

Defining the critical path

As in all construction projects, using the Critical Path Method (CPM) is crucial in order to establish a viable model for the project. However, for HPP projects, the critical path may take different routes depending on the layout. If, for example, the dam is large and the headrace and the tailrace tunnels are short, the critical path is entirely allocated to the dam site. In such cases, it is worthwhile spending major efforts on a quick completion of the diversion tunnel or tunnels. By contrast, when there are long waterways in the dam layout, the critical path will most likely be the headrace or tailrace tunnels, which may call for a number of intermediate adits. If the power station complex is large and dam and waterways are moderate, the time for handover to the owner is ruled by how fast it can be completed. The large openings dedicated to the powerhouse, transformer hall, surge shafts, etc, are all excavated in a number of steps, with the exception of the diversion tunnel openings. These, by contrast, can be created from a number of smaller openings,

86

which may be a more attractive option if the ground conditions are unfavorable. A widely accepted conclusion is that the bench excavation that follows top heading excavation is carried out most economically by vertical drilling of the blastholes. In HPP projects where a large number of tunneling rigs are employed already at an early stage, it is common for the same equipment to be used in benching operations. The excavation is then known as “horizontal benching”. There are cases, however, especially in India, where the Boomer drill rigs are sometimes used for vertical blasthole drilling. As can be seen in Figure 4, the powerhouse is excavated in a number of benches to achieve the full height.

Mucking and hauling

Mucking of the blasted rock is nearly always carried out using rubber-tired equipment, and that means wheel loaders for loading and trucks for hauling. The exception is mucking in vertical structures like the surge chambers and penstocks.



At TBM excavations of the waterways rail-bound mucking is normally employed or, as an alternative, conveyor transport. The large variation of the sizes of the underground openings calls for equipment of different sizes in order to meet capacity requirements. This means that a HPP with most construction elements located underground will have a fairly large equipment fleet. Many of the vehicles will be used only over a short time period and, in many cases, it is favorable for the contractor to rent the equipment instead of purchasing. Other viable options are to subcontract defined operations like the mucking work for defined construction parts. Typical mining equipment such as LHDs are not frequently used in HPP construction. New models, however, are well adapted for small tunnels yet provide high transport capacity. For this reason, it is quite possible and suitable to use LHDs for smaller headrace tunnels, grouting galleries below the dam and where only a short tramming distance of the muck is needed. Normally, front-end mucking is applied to the wheel loaders, but the side-dumping technique has become more and more popular, especially in 6–8 m wide tunnels where front-end loading with high capacity can be troublesome.

Figure 5: The principle of side-dumping at the tunnel face.

Instead of using niches for mucking operations, side-dumping enables convenient loading at the tunnel face, see Figure 5. There are cases where the tunnel cross section has been designed specifically for the side-dumping technique, as shown in Figure 6, where a good advance of the tunnel heading is achieved. One example is the Sauda HPP headrace tunnel in Norway, with a dimension of 38 m2 and a heading length of 5.3 km. The single heading excavation resulted in an average advance rate of 14 meters per day, including pregrouting, in a 20-hour work day.

Vertical structures

Excavation of the vertical structures demands a somewhat different approach, both in terms of extracting the rock and mucking operations. The dimensions and height of surge shafts may vary considerably. A width of 15 m is not unusual and a height of 50–100 m is also common. The usual approach, therefore, is to create access points both at the top and bottom sections. By excavating the top and making a small shaft in the center going all the way down to the bottom using the raiseboring technique, muck can be discharged through the shaft and collected at the bottom. Downward drilling and blasting to widen the shaft to its final size is performed in stages with a height that enables suitable rock support.

as when dropping muck into a central shaft. This method is normally more time consuming due to the extensive hoisting work. The penstock is another vertical or sub-vertical structure that, traditionally, was almost always been excavated by use of a raise climber. Today, however, most penstocks are excavated using raiseboring equipment, especially as the restrictions on dimensions and lengths with this technology are continuously being expanded. Diameters of 6 m and lengths up to 1 000 m can be bored with standard equipment. Having said this, it should be pointed out that high precision is demanded for the pilot hole to meet the targeted position at the bottom. There is a way to overcome this problem and that is to make a primary hole in the center of the shaft using guided core drilling, which can create long holes with a very small deviation.


87


Other methods are also applied such as regular shaft sinking, which means that the full section is excavated from the top down. All muck must then be hoisted out of the shaft, and rock support in the walls is installed in the same manner

Figure 6: An example of a headrace tunnel shaped in such a way that mucking by use of a side dumping bucket will be viable, as was done at the Sauda HPP in Norway.


Raiseboring equipment provides a safe and easy way of excavating large diameter openings. It is commonly used for HPP construction elements such as penstocks and surge chambers.

In addition, there are penstocks that feature only moderate declination and where the slope might be so gentle that the muck fails to slide down the shaft. In these instances, the dicharge of muck has to be boosted by water flushing. There are also moderately angled shafts that have been excavated by specially designed TBMs going from the bottom up. Mechanically excavated shafts offer great advantages as they give a very smooth surface compared to drill and blast excavation. Almost all penstock shafts are lined either with concrete or steel that is backfilled with concrete. A smooth rock surface with only small overbreak gives considerable savings on the concrete.

Rock support for hydropower plants

When it comes to rock support, many of the underground structures are frequently lined with concrete, such as the roofs of the large caverns (powerhouse and transformer hall), as an insurance against unwanted stoppages in power production. The small grouting galleries under the dam’s

88

core are also often given a concrete lining. Whether to use concrete lining for headrace tunnels or not is a frequently discussed topic. In good rock conditions, tunnels excavated by drill and blast are usually not concrete lined as the estimated stability lifespan is at least the same as the lifespan of the power plant itself. If there are rough rock walls where friction losses are larger, this can be compensated for by making the tunnel larger and, thereby, reducing the water velocity and friction losses. The installation of rock support in HPP projects is carried out in the same way as for most other underground structures placed in rock. The main elements are rockbolts, dowels and sprayed concrete that, to a large extent, are reinforced by fiber. Sometimes the fibers are replaced by reinforcement mesh that makes the sprayed concrete tolerate larger deformations. If TBM excavation is the chosen method, concrete lined tunnels are much more frequent and very often the lining consists of backfilled concrete segments that form a circular tube. ◙


HYDROELECTRIC POWER (HEP)

89



Figure 1: A myriad of tunnels for a multitude of purposes such as water and electricity supplies, district heating plants, sewage and drainage lie hidden deep in the ground and out of sight below the world's cities.

The utilities beneath our feet According to some surveys, nearly 70% of the world’s population will be living in conurbations by the year 2050. Water and utility tunnels below our towns and cities are crucial to coping with the increased pressure on municipalities. Few people are aware of the vast and complex networks of tunnels that exist beneath their feet as they go about their everyday lives in towns and cities across the world. But the fact is, without these subterranean tubes, society, as we know it, would simply not function. These are the municipal water and utility tunnels that are never seen but fulfill a major role in urban society. Designed and installed for a multitude of different purposes, they are all quite similar: small in size with cross sections of 10–25 m 2; relatively long with a number of connecting shafts or shorter

90

tunnels along their routes, and built for a very long service life, which is why they are rarely inspected. Another obvious similarity is that municipal water and utility tunnels, as opposed to road or rail tunnels, are not open to the public. However, public curiosity in these tunnel types has increased in recent times following the discovery of some remarkable installations that have long been forgotten in New York, London, Paris and other major cities, leading, in some cases, to guided tours.


WATER AND UTILITY TUNNELS

Water tunnels – three purposes

Municipal water tunnels are designed for three purposes – to carry fresh water supplies, to discharge sewage water, and to take care of storm water by temporarily storing rainwater. As volume is a priority in storm water situations, these tunnels are often large with cross sections in the region of 20–50 m2, while the other two are generally less than 20 m2.

Fresh water tunnels

Freshwater tunnels are mainly located outside city limits as their purpose is to transport water to densely populated areas, which, in many cases, may include a cluster of towns or cities. Lesotho tunnels A good example of this is the Lesotho highland freshwater tunnel where one section that includes more than 80 km of tunnel has been in operation for more than 15 years and has the capacity to transport water at the rate of almost 30 m3/s to the Johannesburg-Pretoria area. The scheme is still expanding, and several sections still need to be completed. The Lesotho tunnels are to be concrete-lined along their entire length. Pahang Selangor The 45 km long Pahang Selangor freshwater tunnel in Malaysia was excavated with a diameter of around 5 m, which is similar to the size of the Lesotho Phase 1 tunnels. In addition, both of these have to a great extent been driven by TBM (Tunnel Boring Machine). The Pahang Selangor tunnel, which was excavated in mainly competent rock, is lined along certain stretches, typically in the sections that have been driven by conventional methods in poorer ground. For more information on the Pahang Selangor, see p. 270. These tunnels are normally designed to be “free-floating” which means that they will not be pressurized. The Päijänne Water Tunnel The Päijänne Water Tunnel in Finland is the world's second longest continuous rock tunnel after the Delaware Aqueduct in the U.S. It is 120 km long, runs 30–100 m below the ground surface and is designed to convey fresh water to more than one million people living in a group of 10 cities, including the capital, Helsinki. The tunnel starts at Asikkalanselkä near Lake Päijänne, which, at roughly 1 000 km 2, is the second largest lake in Finland. As the tunnel slopes slightly downhill, the water flows naturally from its source and the lake water is of such good quality that it is theoretically drinkable without processing.

Municipal tunnels are generally designed for three purposes, to carry fresh water, discharge sewage or, like this one, for temporary stormwater storage.


91


The tunnel ends at the 0.5 km 2 Silvola reservoir in Vantaa, outside Helsinki, where it is pumped to two water treatment plants, one in Pitkäkoski, the other in Vanhakaupunki. Since the constant low temperature in the deep tunnel ensures high quality during transport, only minimal processing is required before use.


Freshwater tunnels are mainly located outside city limits. Their purpose is to transport water to densely populated areas.

Construction of the tunnel started in 1972 and was completed in 1982 at a cost of approximately EUR 200 million. In 2001, sections of the tunnel needed to be repaired due to rockfall, and in 2008, the tunnel underwent extensive renovation including reinforcement measures at the southern section in order to prevent cave-ins. The tunnel has a cross section of 16 m 2, wide enough for a truck, and enables a water flow of 10 m3/s. At current water usage rates, the treatment plants take in water at the rate of about 3 m3/s for drinking water processing. The tunnel will also serve as an emergency reserve in the event of water supply disruption.

25 km in a raw water pipeline before it reaches Ringsköverket where it is treated. The power company Sydvatten started the construction of the Bolmen tunnel in 1975 and it was commissioned 12 years later. A common denominator for the last two tunnels mentioned is that they were both excavated using the drill and blast technique. In the Bolmen tunnel, all of the equipment was rail bound while in the Finnish tunnel rubber tired equipment was used. At the Bolmen tunnel drill rigs were used as the light Swedish method was not considered viable for projects of this magnitude. A number of access points were constructed from where the tunneling operations were performed, and that meant that the heading lengths seldom exceeded 5 km.

The Bolmen tunnel Another interesting example is the Bolmen tunnel in Sweden. The Bolmen tunnel was built during the same time period as the Päijänne tunnel but has a smaller cross section and a slope of 0.1% making it capable of providing a flow velocity of 1 m/s. The tunnel has a cross section of 7.5 m 2 and due to a difference in fall height of 90 m, the water runs by means of gravity all the way from Bolmen to Äktaboden.

Drilling was carried out using hydraulic rock drills mounted on Atlas Copco Promec drill rigs, and the mucking was performed by the continuous loading system Häggloader matched with shuttle cars, all of which were railbound in the Bolmen tunnel to tackle the 7.5 m2 tunnel section. Today, the same concept is used in small tunnels but with equipment that has now been considerably upgraded.

Used to transport water from Lake Bolmen in the county of Småland to Ringsjöverket in Skåne, the tunnel stretches 80 km from the intake of Bolmen in Skeen to Äktaboden near Perstorp. After Äktaboden, the water is transported a further

Sewage tunnels

92

Interceptor sewage tunnels are typically quite long, and they often have a number of connecting shafts or shorter trunk tunnels along their alignment.



Interceptor sewage tunnels are typically quite long and often have a number of connecting shafts which can be effectively installed by raiseboring equipment.

Käppala tunnel Some water tunnels can also be extremely long, such as the 60 km Käppala sewage tunnel in Sweden that was built in the 1960s. This tunnel is also connected to a number of communities along its route to a sewage treatment plant. Pump stations are also used so that the outlet end and the intermediate connections need not be buried very deep in the ground. On the other hand, this type of tunnel is not as sensitive as a road or rail tunnel and can therefore be located deeper underground in urban areas. Gothenburg tunnel A recently completed 8 km long sewage tunnel in the Gothenburg area in Sweden is a good example of how drill and blast technology has improved. This tunnel is used to send untreated sewage water to the main treatment plant of the region. The required cross section was less than 10 m 2 and the contractors were free to bid drill and blast or TBM excavation.

These smaller sewage tunnels often add up to a considerable number of kilometers. Gothenburg, for example, has as many as 130 km of small tunnels meant for sewage. About 700 000 people are connected to the system which works out at 0.2 m of tunnel per inhabitant. If we put this case into perspective globally, bearing in mind that 4 billion of the world’s population live in urban areas, 0.2 m of sewage tunnel per capita would result in 800 000 km of tunnels. If only 10% of that amount needs to be built today, it still adds to an extremely large number of tunnel meters. The majority of these tunnels can certainly be built by microtunneling or pipe jacking, but there is still a huge potential for regular sewage tunnels to be built by TBM or conventional drill and blast tunneling.

Stormwater tunnels

Stormwater can drastically increase the flow of sewage water in sewage treatment plants, which is a common occurrence. As all sewage plants have a capacity limit in terms of water


93


There were strict requirements on the acceptable influx of water into the tunnel which meant that pre-grouting had to be carried out, at least in certain sections of the tunnel. Drilling grout holes is more easily done using the drill and blast method, and an offer proposing the use of the drill and

blast technique was the lowest bid. For tunnels with small cross-sections and a reasonable length, the TBM technique should normally beat conventional tunneling on price. In this case, the required sealing probably made the TBM alternative less competitive.


Most municipal utilitiy tunnels are limited in size and require specially designed excavation equipment, such as the continuous loading system Häggloader from Atlas Copco.

flow, the consequence may be that improperly processed water is discharged into the receiving source, a lake for instance. By buffering the stormwater and feeding it through the plant in a moderate flow, the treatment of the sewage can be made in accordance with required standards. By excavating chambers large enough to hold the rainwater for a defined area, the buffering effect is achieved. To achieve this, the chamber has to have suitable connections to the existing sewage water net. For 50 mm of rain, the required storage is 50 000 m3 for every square kilometer. This method of buffering storm water is only needed in densely populated areas where vast areas of the surface ground area are paved over, meaning that water cannot be filtrated into the ground in the natural way. These conditions are found in larger cities where more than two-thirds of the geographical area is covered with paved surfaces. Chicago is a good example of a city that has invested heavily in an extensive water storage system. In this particular case, no caverns have been excavated but, instead, enlarged sewage tunnels that have the capacity to absorb large stormwater volumes.

94

Chicago Deep Tunnel Chicago’s TARP system (Tunnel and Reservoir Plan) ranks as one of the largest civil engineering projects ever undertaken in terms of scope, cost and timeframe. Commissioned in the mid-1970s, its aim is to reduce flooding in the metropolitan Chicago area and to reduce the harmful effects of flushing raw sewage into Lake Michigan. Although completion of the system is not anticipated until 2029, several sections of the system are operational and currently divert storm water and sewage into temporary holding reservoirs. More commonly known as the Deep Tunnel Project or the Chicago Deep Tunnel, the mega project has received more than USD 3 billion in financing so far. Phase 1 of the project was established in 1972 and included the tunnel construction adding up to 176 km (109.4 miles), ranging from 2.7–10 m in diameter and located about 100 m underground. The work on Phase 1 commenced in 1975 and was completed in 2006. Phase 2 involves the creation of reservoirs that are primarily intended for flood control. This phase is under construction and is due for completion in 2029. Currently, up to 9 million m 3 of sewage can be stored and held in the tunnels themselves while awaiting processing at sewage treatment plants, which release treated water into the



Calumet and Des Plaines rivers. Additional sewage is stored at the Thornton Transitional Reservoir with its capacity of 66 million m3. It will return to use as a quarry when the nearby Thornton Composite Reservoir is completed.

Power line tunnels

It is quite common that high voltage power lines cross urban areas in the open air. The magnetic field generated by the electricity makes living in the immediate proximity of the line unhealthy and the land cannot be utilized. This means that useful space has become wasteland. By relocating power lines to underground tunnels, large areas of real estate can be freed up for housing developments. In city areas where the price of land is high, locating power lines underground is self-financed. These power tunnels typically have a cross section of some 15 to 20 m 2, which makes vehicle transport possible after power cables have been installed. The alignment of these tunnels can easily be adjusted to fit the situation underground. They can also go deeper to avoid collision with metro lines, sewage tunnels or other utility tunnels, such as those used for district heating and telecommunications. London power grid The planned, new power grid for London is a good example. The excavation technique being employed here is with TBMs due to their capability for dealing with the over-consolidated London clay which cannot be excavated by drill and blast. The UK’s National Grid explains it as follows: It is National Grid’s responsibility to ensure there is sufficient transmission infrastructure available to support future energy demand in London and, as part of our investment programme, we are planning to build four deep tunnels which will house new 400 000 volt (400kV) cables. The work is essential to ensure London has a safe and secure electricity transmission network into the future.

Expansion essential

When it comes to energy, and specifically renewable energy, the production site is often a long way from where the energy is needed. It is, therefore, paramount that existing networks be expanded. Buzzwords such as “smart grids” have long been in existence. These intelligent grids will manage future power generators and storage facilities using state-of-the-art information technology. An intelligent and highly efficient underground alternative for energy transportation is power tunnels such as the one currently being built by the Leighton subsidiary Thiess for Australia’s largest energy supplier, Ausgrid. With a diameter of 3.5 m, the 135 kV tunnel will link the City North substation with a new substation. The tunnel runs 25–45 m below Sydney. The contract is worth the equivalent of EUR 100 million. Along with building the tunnel, the project also involves the construction of two concrete lined connectors, constructing a link to the City South cable tunnel, and the installation and operation of mechanical and electrical services. Completion is scheduled for 2015.


95


Why a tunnel? In London, most electricity is transmitted through underground cables. These are traditionally located just beneath the road surface, and maintenance work on them is carried out in the road. By housing new electricity cables in tunnels deep below the road surface, a number of advantages can be gained compared with traditional methods. These include: • Major disruption to the road network throughout London is avoided as it is not necessary to dig up the streets to lay the cable • Overall disruption to Londoners and road users during construction is significantly reduced as the majority of the work takes place underground • Future repair and maintenance work can be carried out without disrupting traffic, businesses and residents • Additional cables can be installed in the tunnels to meet future demand

With a compact design, four-wheel steering and an ergonomic cabin, the Atlas Copco Häggloader is optimized for haulage in long narrow tunnels.


District heating

Other utility tunnels are being built for district heating purposes. District heating is a large-scale method for the production and distribution of heat. The heat is produced in a central production plant and distributed via a pipeline system to consumers in apartment buildings, offices or housing areas, where it is used for heating purposes via radiators or for the production of hot tap water. District heating is based on economies of scale, i.e. a large system supplies heat to many users within a certain geographical area, e.g. an urban area. Compared with smallerscale alternatives, heat production in a district heating system is more effective and, therefore, uses less fuel, giving both economical and environmental advantages. It allows for the simultaneous production of electricity and more advanced exhaust cleaning. For the consumer, it is a simple form of central heating that requires a relatively limited amount of work. District heating is primarily common in Northern and Eastern Europe. In the rest of Europe district heating occurs in varying degrees. Outside of Europe, district heating systems are found in the U.S., Canada, China, Japan and South Korea.

Drill rigs used in small tunnels usually consist of two-boom drill rigs, but often without service platforms due to the limited space.

The growth of district heating (DH) systems in the heating market varies from country to country. This penetration is influenced by different factors such as environmental conditions, availability of heat sources, economics, and economic and legal frameworks. Among the prerequisites for an expansion of district heating systems are an existing heating market, i.e. a climate with cold winters that creates a need for heating, and that the demand is so geographically concentrated that the heat can be distributed at a reasonable cost. A demand for heat as well as electrical power has a positive effect. In order to distribute the heat, a network of pipes is required. This can be located on the surface or underground. From an esthetics point of view, locating these networks underground is the method of choice in many countries. A network has mains and branches of various sizes.

Multipurpose tunnels

There are multipurpose tunnels containing telecommunication lines, electrical lines and possibly district heating pipes, as well as cooling pipes and freshwater mains. Some tunnels are built solely for telecommunication purposes. These have small cross sections of about 8 m 2 that are possible to excavate using conventional tunneling methods.

High capacity LHDs are perfectly designed for mucking out in small tunnels.

96

For small tunnels with cross sections of 9–15 m 2, railbound equipment is frequently used. For shorter ones, less than 1 km long, rubber tired equipment is a more practicable alternative,



Photo: Courtesy of BASF

Sprayed concrete may be of the dry-mix type or, as used here, of the wet mix-type. A tunnel of this size only requires a small quantity to be sprayed for each round.

although for the tunneling equipment it will involve a lot of tramming back and forth. Longer tunnels excavated by conventional drill and blast have successfully applied the concept of operating at two headings from an access tunnel. Larger utility tunnels of 15 m 2 or more mainly use rubber tired tunneling gear. The approach is very similar to what has been described in the chapter "Road and rail tunnels", p. 68. The sequential operation is the same and the major difference is within the set up of the tunneling fleet. The units are smaller in order to fit into the tunnel sections and have more in common with the fleets being used in mine drifts.

Mucking is favored by the low built, high capacity LHD units, which have a better capability to penetrate the muck pile and a better load-carrying capacity than corresponding

The concrete spraying equipment used maybe of the dry mix type as only small quantities need to be sprayed for each round. Besides that, the logistics become simpler and this, in many cases, will outdo the wet mix type, despite all other disadvantages (see discussion in the chapter "Rock reinforcement", p. 150). Dry mix sprayed concrete can not only be left on standby but is more suitable to small batches and for ad hoc efforts as it is delivered in a ready-made dry mix. There are small bolting units available, but these are rarely used, as opposed to mines where they are frequently employed. The explanation is the low utilization due to the low number of available headings. ◙


97


The drill rigs normally have two booms with rock drills but the service platform might be omitted due to the limited space. Charging is done using bulk explosives, but cartridge explosives may still be used in some parts of the world.

standard wheel loaders designed for surface operations.The height of the wheel loaders makes it difficult for them to operate in these small tunnels. There are smaller wheel loaders available, however, but these cannot effectively deal with blasted rock.

4

1 2

1 Access tunnel 2 Infiltration galleries 3 Storage caverns 4 Portal

3

Figure 1: Typical layout of an underground storage facility. Several caverns may be placed in parallel and can also have different purposes such as the storage of oil, 1 Access tunnel gas and other natural resources. 2 Water curtain tunnel 3 Storage caverns 4 Portal

Rock caverns for hydrocarbons Underground rock caverns have been used for years for storing oil and gas. They require a high level of skill and experience to construct, but the result is a storage solution that is environmental, safe and economical. Underground facilities for the storage of oil products in unlined rock caverns were developed in the 1950s as a better alternative to tanks on the surface. The objective was to make the storage of oil safer, cheaper, more strategically located and with less environmental impact. These advantages have since proved to be unbeatable, and underground caverns are still considered the most favorable storage alternative for all hydrocarbons. Constructing them, however, is a major undertaking requiring a high level of skill and experience.

98

The first patent application to store oil products in a manmade, unlined rock cavern was put to the test with the construction of such a facility on an island in the Stockholm archipelago in Sweden. The evaluation results showed conclusively that the product and the environmental impact had satisfied all requirements and neither the product nor the environment had been contaminated. It took some time before construction of underground storage facilties for commercial purposes could get underway and one of the first of these was located in the coastal town of Nynäshamn, south of Stockholm.


OIL AND GAS CAVERNS

Oil and gas caverns are excavated using the sequential technique of top heading coupled with bench drilling. Surface drill rigs such as this Atlas Copco FlexiROC T20 are used in the bench drilling stage for drilling vertical blastholes.

The containment concept is based on the principle that rock and water jointly keep oil or gas trapped within the excavated cavern without any form of lining. The rock itself is the structure and water is the sealing medium, filling up all cracks and fissures even above the roof. This situation is then maintained by the groundwater. Its surface should be well above the crown of the cavern. In order to be sure that all discontinuities are properly filled with water, there has to be a small but steady flow of water into the cavern. If that is not the case, the natural method, i.e. rainwater infiltration, has to be supported by artificial infiltration using separate galleries and holes filled with water under pressure located above the crown of the cavern, as shown in Figure 1.

Different caverns

There are also different types of rock cavern storages for hydrocarbons, of which the most common is for the storage of liquids, followed by caverns for liquefied petroleum gas (LPG) and then crude oil. Crude oil storages are fewer in number but often hold large volumes in the magnitude of millions of cubic meters. There is a fourth storage type – caverns for liquefied natural gas (LNG) – which at present has very limited applications. These facilities for gas storage have to be pressurized to ensure that the gas remains in a liquid state and are typically used for LPG products, propane and butane. To be able to store gas in a liquid state, the storage has to have a minimum pressure that is defined by the type of gas and the ambient temperature of the cavern. These pressures


99


Normally these infiltration galleries are located about 10 m above the crown of the cavern and they are supplemented with horizontal infiltration holes. It is often the case that a number of caverns have been built in parallel but have different owners. In this case, vertical infiltration holes are located

in between the caverns with the aim to stop any possible migration of products from one room to another.

OIL AND GAS CAVERNS

Vapour overpressure, MPa 1.5

1.0

.3

.2

.1

0.02

0.02

75 /25

/5 0

10 0/1 0

Figure 2: Minimum pressure levels required for gas stored in rock caverns. Environmental • Invisible • Better control of spills and vaporizations • Better energy control • Strategic options

Safety • Limited impacts of accidents or malfunctions • Protection against attacks and sabotage

Economical • Reduced land appropriation • Longer service life • Lower cost for operation and maintenance

• Stable storage conditions

Table 1: Typical benefits of rock caverns.

1.5

10 0/1 0

ne

Buta ne

Mi xb ut an 0/ e /p 1 Mi 25/7 00 ro pa 50 x b 5 /5 u 0 ta 75 n /25 0/ e / 1 25 00 pro / pa 50 75

ne

Buta ne

1.0

Prop ane

.3

.1

Prop ane

.2

0.02

0.02

Temperature ˚C Temperature ˚C

0.01 0.01 0 +10 +20 +30 +40 -50 -40 -30 -20 -10 0 +10 +20 +30 +40 -50 -40 -30 -20 -10

Vapour overpressure, MPa

are exhibited in Figure 2. Such a facility with 100% butane gas requires an overpressure of 0.07 MPa at an ambient temperature of +10° C. This means that some 7 m of water pillar or 0.7 bars of water pressure is required in the crown. The corresponding figure for propane is 60 m. Some extra meters of water pillar have to be added to cover up for the variation in temperature and uncertainties in maintaining the height of the water pillar. Alternatively, the temperature of the gas can be lowered in order to keep it in a liquid state. If the gas is to be stored in a rock cavern at an atmospheric pressure, the seepage of heat from the rock to the liquid gas must be prevented to avoid the cost of refrigeration from rising to an unacceptable level. When transporting gas by sea, refrigeration is a frequently used method of keeping the gas in a liquified state. Hydrocarbon rock storages are often located in coastal regions so that they can be recharged from cargo ships. The distribution of products from these storage facilities is via smaller sea vessels, trains, trucks and pipelines. Due to the advantages offered by underground storing of hydrocarbons, the method is of interest to all parties involved in the handling of these products. Compared with surface tank storage systems, the environmental, safety and economical advantages of underground rock caverns are irrefutable. The main benefits are listed in the table, to the left. The typical layout of a rock cavern storage facility is shown in Figure 1. It is often the case that a number of caverns are built in parallel with lengths ranging from 400 to 800 m. Accessing the caverns at three or four levels is provided by downhill tunnels. Some storage facilities have caverns for several purposes and products, such as diesel, gasoline and jet fuel. In such a case, the jet fuel tanks would be built like vertical cylinders with the aim of minimizing the mantle surface for a given storage volume. The aim of this design is to minimize the possibility of bacteria attacking the stored fuel. Contact between water and fuel can only take place along the cavern surface, mainly at the bottom. In order to minimize the risk of flourishing bacteria, the interface area where fuel and water meet should be reduced as far as possible.

Design and construction

Storage facilities for hydrocarbons are often located in coastal regions near ports, so that they can be recharged from cargo ships.

100

When designing and building storage caverns there are generally fewer limitations than in the construction of tunnels for roads and rails. There is more freedom to select suitable sites from a geological point of view and this can be decisive for the economy of the facility. The caverns are generally unlined and the owner is basically only interested in volume capacity, which means that overbreak only translates into extra volume. However, this does not mean that reckless drilling and blasting is permissible because that always results in excessive costs for rock support. Instead, it means that when


OIL AND GAS CAVERNS

Access tunnels for oil and gas caverns need to be well-designed with hard ground surfacing in order to support the flow of large haulage equipment during construction.

poor ground conditions are encountered, the excavation can be terminated at that position and restarted elsewhere (unless strict boundaries are specified for the cavern installation). This also makes it possible to alter the design locally, provided the objective of the storage facility is maintained. One consequence of this strategy is that the designers must look for a site that is characterized by good rock conditions that are stable and yield very small quantities of water influx. All water that is leaking into a cavern has to be pumped out and passed through a purification plant before it can be let out or infiltrate the ground surrounding the facility. Pumping and treatment of water is a costly item and, therefore, a very ambitious study on the hydrogeological conditions is a must for all hydrocarbon storages. Local zones with increased water influx can be treated by use of pre-grouting.

Constructing a rock cavern storage facility is a large-scale underground excavation. That means that large equipment will be used to bring the building costs down. This also has

It must be kept in mind that cavern construction is, to a very large extent, a muck-shifting task. It is not unusual that 2 million m3 of muck has to be removed in 18 months during the benching phase of the excavation. That is roughly an average of one 30-tonne truck with rock spoil coming up to the surface every three minutes. The access roads are, therefore, often given a hard surface of tarmac or concrete. A well-designed access tunnel can be seen in the photo above where the surface is very compact and hard, which is crucial in order to adequately support the continuous flow of heavy haulage equipment during construction. The demand for fresh air is high as many large combustion engines are busy working underground. In the first phase of the project, fresh air is normally supplied via vent ducts located in the roof of the access tunnel. The combination of large equipment for excavation and large vent ducts makes it necessary to have accesses with a cross section that goes beyond normal praxis for access tunnels and cross sections of 80 m2 are not unusual.


101


Major undertaking

implications for the access tunnels as these must be large enough to take intense traffic consisting of large hauling equipment traveling at a reasonably high speed.

OIL AND GAS CAVERNS

10 m

10 m

10 m

20 m

Figure 3: In the construction of large caverns, 30 m high or more, the excavation sequence is split into three or four stages. Top heading excavation is the first stage (see top right) followed by the benching technique. This illustration shows a three-stage excavation.

The downhill access tunnel has a slope of 10–12%. Steeper slopes will hamper the speed of the fully loaded trucks as they drive uphill. For a 30 m high cavern, which is a common height, the excavation has to be split in stages. There can be three or four stages, where stage one is called the top heading. The other two or three stages are for benching. This means that for each stage access has to be provided to the base level for drilling and blasting as well as mucking. It is therefore normal to branch off from the descending access tunnel at those defined levels. This is visualized in the three-dimensional sketches on storage layout shown in Figure 3 and 4. The excavation of the top heading has much in common with road tunnel construction, although the tolerance on the contour is not so strict. It is a very wide tunnel, usually 20 m, and it is not uncommon to split the face in two or three parts where one part is advancing two to three rounds ahead of the other. This gives more headings to work on and better opportunities to improve the utilization of the equipment and, consequently, achieve a higher advance rate.

102

Besides this, today’s drill rigs are not capable of reaching all the holes to be drilled from one position. This means that the rig has to be repositioned to cover the whole face. In good ground conditions, 5 m long rounds are common. The height of the top heading depends on how the bench excavation is planned. If a four-stage excavation is planned, the top heading will normally be some 7 to 8 m high. This height will provide easy drilling of bolt holes 5 m in length, which is considered adequate for this size tunnel in good ground conditions. The definition of three- and four-stage excavation is shown in Figure 3 and 4. Note that the illustration is chronologically compressed as all the excavation stages are shown in one photo/diagram, whereas, in reality, each stage is completed before the next one starts. It is also possible to excavate all stages by use of horizontal blasthole drilling. This is sometimes preferred when the ground requires heavier support in the rock walls. The three-stage excavation aims for a 10 m high top heading. This makes it possible to go for vertical bench drilling on the first bench. In good rock conditions, it saves time to


OIL AND GAS CAVERNS

7.5 m 7.5 m 7.5 m 7.5 m

20 m

Figure 4: In a four-stage excavation, the top heading is normally 7-8 m high, which facilitates the drilling of bolt holes. Each stage is normally completed before the next one begins.

go for higher benches and vertical drilling of the blastholes. This concept offers the advantage of continuous mucking as the drilling work can be performed in parallel. The drill rigs of today have the possibility to drill horizontal holes as high as 13 m above the ground. For this type of drilling task large computerized rigs are the most suitable. Certainly the so-called DCS (Direct Control System) rigs will do the job as well, but their precision is inferior which will call for increased support and more time-consuming, hands-on work.

The excavation of these large cavern benches has more in common with large-scale mining than regular tunneling. But there are parts of the storage that are typical tunneling jobs, namely the access and infiltration gallery construction. The excavation equipment being used in the cavern’s top heading can be utilized for the access excavations, provided they are large enough. The infiltration galleries, which will have cross-sections in the region of 15–20 m2, need smaller equipment. The construction time for a large storage cavern is three to four years, including the installation of mechanical and electrical equipment. ◙


103


For mucking, wheel loaders with a 10-tonne bucket capacity are the right tools to use, in combination with trucks with a bed capable of transporting at least 30 tonnes. For bolting, normally the drill rigs mentioned above are the correct equipment to use, but in the event of extensive bolting, separate bolting rigs are recommended. The reason is threefold: the quality of the bolt installation, the difficulty of manually handling the 5 to 6 m-long bolts and the type of excavation, consisting of several caverns that offer many faces to work on for a bolting unit. This makes it possible to fully utilize the Boomer rigs on face drilling and drilling for pre-grouting where needed.

As large rock surfaces are being exposed at high speed, only high-capacity wet mix concrete spraying equipment should be considered. For scaling, mechanical scaling should be used. Normally rubber wheel excavators with a hydraulic breaker taking the place of the bucket are best suited for this task due to their high reach and mobility.

Figure 1: A 3D overview of how the space below ground in cities can be utilized to great advantage, ranging from sports arenas and parking garages to storage facilities.

The rising role of subsurface space

As people flock to the world’s big cities in ever-increasing numbers, the utilization of subsurface space is emerging as the only sustainable solution for preserving the quality of urban life. There are now more than seven billion people on the planet, and according to the experts, this is likely to rise to more than 9 billion by 2050. The figures may not be especially alarming in themselves, but the current rate of migration to the world’s big cities poses a serious threat to the quality of urban life. It’s a threat that cannot be ignored. For many communities already under pressure to improve the quality of life for their citizens, a constant stream of new arrivals is presenting major challenges on almost every level. Not only does it increase the

104

pressure on municipal services such as mass transit systems, it also dramatically ratchets up the human need for just about everything else – accommodation, food, water, lighting, heating, health care, education, and so on. The big questions are, therefore: how will the world’s municipalities cope with the burden of absorbing more and more residents each year and how will they be able to achieve it in such a way that will sustain and protect the quality of life over the long term? One solution – and it is rapidly looking like


UTILIZATION OF UNDERGROUND SPACE

the only solution – is to dramatically increase the utilization of underground space.

Innumerable benefits

Subsurface space is, of course, already widely used in modern society for such amenities as municipal drinking water, sewage systems, district heating plants, subways and telecommunications – but there’s ample room for more. As a result, some urban planners are urging politicians to prioritize investments in underground construction in a bid to preserve the quality of city life for future generations. It is easy to see the wisdom of such investments. Roads are a typical example. More roads mean more vehicles, which generally mean more noise and more pollution. To locate a greater portion of city road systems in tunnels is a perfect solution from almost every viewpoint, and it is not necessarily a great technical challenge. The technology and expertise required for this already exists. The same goes for parking lots, railways, power lines, power stations and other amenities. In addition, placing as much as possible below ground is not only more aesthetically and environmentally beneficial, it also frees up valuable real estate on the surface, enabling more green areas and other pleasant surroundings to be created for people to enjoy. In this context, the following benefits are strong arguments in favor of placing as many facilities as possible below the surface: • Underground rock caverns provide unparalleled protection for municipal stores, city archives, shelters, garages, trans former stations and defense installations. • Railway networks can operate in tunnels without being adversely affected by surface traffic or unfavorable weather conditions. • Wastewater treatment plants can be built close to residential areas, thereby avoiding the cost of long-distance transpor tation. • Large construction projects can be carried out in city cen ters without causing disturbance to traffic or polluting the environment with excess dust and noise. • Unattractive or otherwise objectionable facilities that might cause opposition and conflict are more likely to be tolerated if built underground and out of sight.

It also naturally follows that the availability of additional space below ground constitutes valuable real estate. This could be highly desirable for commercial businesses in city

Top: A Boomer drill rig at a Hong Kong construction site, driving a tunnel from a parking garage to the subway. Below: Facilities such as parking garages are suitably placed underground.


105


There’s also another aspect to utilizing the subsurface that should not be overlooked. Vital installations, such as communication cables, data transmissions lines, fiber optics, internet networks and so on, can be installed in tunnels, eliminating the risk of damage from road maintenance work, surface construction, vandalism or even sabotage.


centers that wish to expand, especially if the only alternative is to relocate to another area.

Getting the message

At the same time, it should be pointed out that some decisionmakers are now getting the message, and the advantages of subsurface space are increasingly being realized around the world – from the complex road and rail networks under construction in the U.S., Germany, Sweden and Switzerland to the giant rock caverns in China that are mainly for municipal storage purposes. Other examples include the Stockholm bypass highway and the Stuttgart railway bypass, which is constructed partly in tunnels and features a new underground station that has been excavated using the cut and cover technique. Chicago’s tunnel and reservoir plan (TARP) for drainage water management and the new underground subway line at New York’s Grand Central Station are two further cases in point. As one town planner puts it: “It makes sense to put every facility underground that does not have a good reason to be on the surface.”

Subsurface safety

Safety is a major concern these days, and many also believe that subsurface space far outstrips the surface in terms of providing a safe environment for locating certain facilities. For instance, underground factories, shopping centers, hospitals and even nuclear power plants are all considerably less exposed to the effects of earthquakes, storms, floods and terror attacks. Nuclear power plants are an interesting case in point. With the advantage of modern technology, an underground nuclear facility can be constructed in such a way that the energy released from an earthquake can pass right through the structure, affecting it only at the entry and exit points, but leaving the core buildings, such as the reactor, completely intact. This theory can be visualized using the familiar Newton cradle. By lifting and releasing one end-ball, the full force of the impact travels right through the line of balls and only affects the end-ball at the other end, with all of the balls in between left only marginally disturbed. Scientists also agree that should an underground nuclear plant experience a radioactivity leak, it would be easier to contain than on the surface. This means that the scope of the accident that occurred at Japan’s Fukushima power plant in 2011 would have been much less disastrous if the plant had been placed underground and inside rock.

Assessing rock caverns As cities become more densely populated, a wide range of facilities will be developed underground.

106

In good quality rock, underground caverns have been excavated to widths of 30 to 35 m with only a minimum of reinforcement. However, in sedimentary rock such as limestone, this span is restricted to 15–25 m. The largest natural



Beneath the busy streets of London more than 42 km of tunnels are being constructed for the Crossrail commuter railway line. It ranks as the largest construction project in Europe and involves more than 40 construction sites, including this site at Moorgate.

limestone caverns in the world differ widely in size. Some are 100 m wide or more, and the largest known cavern, the Sarawak Chamber in Borneo, measures an astonishing 390 x 690 m. Although these caverns lie beyond the scope of today’s technology, they give an idea of the underground potential. Location and purpose are two factors that determine the feasibility of any cavern construction project, combined with the eventual commercial value when in use and overall financial circumstances. An oil storage facility, for example, would warrant a cost/benefit analysis, which, if possible, would take into account similar installations that have already been constructed. Using existing references is particularly valuable when decision-makers have no prior experience with underground construction.

However, if the installation will function as a public facility, such as an underground shopping center, and form a part of society, qualitative considerations should be involved, and

A unique characteristic of underground installations is their extreme freedom of geometrical form. Caverns can be large, wide, deep or compound, and long tunnels can be built in any direction. The constraints of surface structures, which determine the construction of all surface buildings, do not apply underground. Made-to-measure, three-dimensional rock caverns offer incomparable advantages. In some countries, this independence from the surface brings benefits in terms of real estate legislation. Even though the tunnels may pass under a large number of properties, wayleave for water tunnels and building permits for the entire route can sometimes be obtained in a single decision, saving valuable time.

Geoplanning / Active design

The planning process for tunnels and rock caverns differs fundamentally from the planning of ordinary buildings; the construction material – the rock– is initially unknown and requires investigation. The aim here is to obtain as complete a picture as possible of the site conditions and to arrive at a technical and economic evaluation of the project.


107


Many types of installations are constructed underground solely for economic reasons. Oil stores, hydropower stations and other commercial installations are often built below ground even though an underground location is not strictly essential.

these have to be evaluated from many other standpoints rather than purely economics.


Urban construction projects often require equipment that is easily transported yet capable, such as this FlexiROC T15 R tophammer drill rig that weighs less than 3 tonnes.

If the intended purpose of the structure allows, step one is to adapt the position and alignment of the installation to suit the local structure of the rock. Step two is a matter of selecting a suitable excavation method and checking the need for reinforcement and sealing measures. Investigations do not cease, however, when the excavation has started. On the contrary, the rock is now exposed and can be observed throughout the construction period. It can later be inspected at certain intervals during the lifetime of the facility in the same way as ordinary buildings are inspected. This continual process of adapting the design to the rock is called “geoplanning,” although the designation “active design” is also being used more frequently. In addition to the design aspects, geoplanning / active design includes studies of the effects on the surroundings in terms of stability, effects on groundwater conditions, etc. Most crucial in the planning stage is the site selection and orientation of the facility in accordance with the actual rock structure. This is because it often has a major influence on the total economy of the project. Great savings can be made by undertaking appropriate studies at the initial planning stage;

108

i.e. during the feasibility and siting studies. This is where expensive mistakes can be avoided.

Overcoming the obstacles

Increasing the utilization of subsurface space is, therefore, a smart way of preserving the urban environment of today while, at the same time, improving it for generations of city dwellers to come. At the same time, it must be conceded that there are obstacles. Not all countries or construction sites have sufficiently competent rock formations to support underground installations, and the cheapest construction proposal is often the one that gets priority in municipal development programs. Despite this, modern technology offers many innovative and effective ways of dealing with unstable ground, and the cost of building underground is now much more favorable. In the 1960s, it was estimated that the cost of building an underground nuclear plant was only 5% more expensive than building it on the surface. Today it is even less, and considering the advantages to society of underground construction, that’s probably a price worth paying. ◙


109



Figure 1: One of several possible methods for final deposit of radioactive waste. Spent nuclear fuel is deposited deep underground and encapsulated in copper canisters, placed inside bentonite buffers.

A suitable resting place for nuclear waste Disposing of radioactive waste is a dilemma that has eluded the world’s nuclear power industry since it began some 50 years ago. Now the world’s first repositories for the long-term storage of spent nuclear fuel are about to be implemented. Compared to all other alternatives, nuclear power is undisputed as the number one method of providing the world with the vast amounts of energy it needs. Handled properly, experts are agreed that it is the cleanest, cheapest and most efficient form of energy currently available. Unfortunately, however, it has a few major disadvantages. The energy produced by the nuclear power industry produces a highly dangerous form of radioactive waste that poses a threat to the environment and to human health for thousands of years into the future. Tailings from uranium mining can also be extremely hazardous if not stored properly.

110

Since the early days of nuclear energy more than 50 years ago, scientists have been grappling with the technicalities of disposing of radioactive waste in a manageable, safe and acceptable way. It has proved to be an extremely hard nut to crack, not only because of the complex requirements involved, but because any proposed solution must also be politically and socially acceptable. In this sense, it can be argued that nuclear waste management is one of the most important issues of the 21st century since the decisions taken today on how to deal with it will


RADIOACTIVE WASTE DEPOSITS

inevitably impact a great many generations to come. At the same time, the search for a universal solution is becoming increasingly urgent as the use of nuclear energy as a central power source continues to expand across the globe.

Waste management today

In this context it is useful to understand that there are different levels of nuclear waste ranging from short-lived waste, such as material from research or medical facilities, to lowlevel waste, such as items that have been contaminated with radioactive material, through to intermediate waste from a variety of industrial processes and high-level waste in the form of spent nuclear fuel from the nuclear power industry. The total amount of high-level nuclear waste currently in the world today has been estimated at 250 000–300 000 tonnes – a figure that is growing by the day. The waste must be completely isolated and confined from human beings and the environment for a very long time. Nuclear waste storage times are based on quantitative analyses for the first 100 000 years, and a combination of qualitative and quantitative analyses for the period up to 1 000 000 years. The guiding principle is that the annual risk of exposure to cancer or hereditary effects shall be no higher than one in a million. Converted into dose rates, the requirement is equivalent to about one percent of the natural background dose in Sweden, to give one example. This waste is currently placed in interim storage facilities that are normally located on the surface and close to nuclear power plants. Water pools or ventilated dry facilities are used to cool the spent nuclear fuel before further treatment through either direct final disposal or reprocessing and final disposal of the remaining waste. Cooling before direct disposal is typically designed for some 40–60 years. Reprocessing may take place sooner than that but requires cooling of the remaining waste before final disposal. The temperature in the repository is set according to the size of the canister, with a dedicated thermal power aimed at a maximum of 100 degrees Celsius. In most nuclear-powered countries such as France, Britain, Germany, Japan, Sweden, Hungary and the U.S., these interim storage facilities are used for storing waste exclusively from domestic production, although some facilities do accept waste from other countries that lack interim storage facilities of their own.

Extensive underground excavation is required for radioactive waste deposit.


111


However, spent nuclear fuel or waste from reprocessing cannot remain in interim storage indefinitely and must be moved to permanent storage sites as soon as possible. These permanent storages must be located deep underground in solid bedrock in stable areas without volcanic or seismic activity. Furthermore, they must not be located in bedrock that is eroded or porous, which might cause groundwater ingress.


Investigations are carried out from the surface to locate the most suitable host rock formations for nuclear waste.

A world first for Finland

Against this background, the Nordic countries, with their excellent quality bedrock and low vulnerability to geological disturbances, have taken the lead in this field. Notably, Finland and Sweden have collaborated in the development of permanent repositories for direct disposal of spent nuclear fuel. As a result, the world’s first final repository for spent nuclear fuel is currently under construction in Finland. Appropriately named Onkalo (meaning “hiding place”), this facility is located at Olkiluoto, some 300 km northwest of Helsinki, and is a joint research program between Posiva, the Finnish nuclear fuel and waste management expert, and its Swedish counterpart, SKB. The Onkalo repository is expected to be backfilled and decommissioned in the 2100s. It is designed to store highlevel nuclear waste for up to 100 000 years. Sweden will not be far behind if plans get the go-ahead, after decades of research, to establish a permanent (final) repository at Forsmark, 120 km north of Stockholm. According to SKB’s plan, construction of the final repository aims to begin in 2019 and the facility is expected to be operational by 2029, providing a storage capacity of 200 000 m3.

112

The common denominator for these facilities is a complex system of underground tunnels constructed in solid bedrock, backed up by extensive scientific research and cutting-edge tunneling technology.

The Swedish approach

In Sweden, the Nuclear Fuel and Waste Management Co. (SKB) is responsible for nuclear waste management from the time the waste leaves the nuclear power plants. The company has developed a system for the safe handling of all kinds of radioactive waste from Swedish nuclear power plants and other Swedish sources for the foreseeable future. The cornerstones of this system are a central interim storage for spent nuclear fuel (Clab); a final repository for short-lived, low and intermediate level waste (SFR); and a sea transport system (M/S Sigrid). SKB aims to implement its plans for both the Forsmark repository and a repository for other longlived radioactive waste. SKB has developed the KBS-3 method for final disposal of the spent nuclear fuel (Figure 3). This is based on the multi-barrier system featuring encapsulation of the fuel in



SFR with harbour

Rock heap

Operation area

Ramp Shaft

Central area

Repository area

Courtesy of SKB, Illustrator: LAJ Illustration

Figure 2: The plan for a final repository near the Forsmark nuclear power station in Sweden.

corrosion-resistant copper canisters and placement of the canisters inside a bentonite buffer at a depth of about 500 m. The primary safety function of the repository is isolation, and the secondary safety function is retardation. The main role of the canister is to provide isolation, and the main role of the host rock is to protect the canister and the buffer so that the isolation is maintained. In the event that the isolation is breached, the buffer and the host rock should retard and disperse escaping radionuclides.

Suitable rock

After decades of site screening, the “tectonic lens” close to the Forsmark nuclear power station was found to provide the

The deposition areas, which together comprise the repository area, will be located about 470 m below ground level and consist of a large number of deposition tunnels with bored deposition holes in the bottom of the tunnels. The positioning of the deposition tunnels, as well as the spacing between the deposition holes, is determined on the basis of the properties of the rock, for example, fractures and thermal properties. The surface facility consists of an operations area, rock heap, ventilation stations and storeroom. When the canisters arrive at the repository, they are transferred to a specially built transport vehicle that carries the canisters down to the deposition level via a ramp. There, the canisters are transferred to a deposition machine to be transported out to the deposition area and finally deposited. After the canisters have been placed in the deposition holes, surrounded by bentonite clay, the tunnel is backfilled with


113


Most of Sweden is located on the Fennoscandian shield where granites and gneisses provide suitable host rock formations. Investigations since the 1970s have provided substantial knowledge on conditions in granitic and gneissic rock that has been used in several safety assessments. Based on these assessments, bedrock properties of importance for isolation and retention, i.e. the safety functions that should be supported by the host rock, have been identified.

most favorable conditions for repository safety. The final repository will consist of a surface section and an underground section (Figure 2). The underground section consists of a central area and a number of deposition areas plus connections to the surface in the form of a ramp for vehicle transport and shafts for elevators and ventilation.


Backfill

Rock

Buffer Canister

Courtesy of SKB, Illustrator: Jan Rojmar

Figure 3: The principle of vertical deposition of canisters, using the KBS-3 method.

swelling clay. Other openings are also backfilled when all spent nuclear fuel has been deposited. The KBS-3 method entails that the canisters can be either vertically (KBS-3V) or horizontally placed (KBS-3H). The reference design of the KBS-3 method is based on vertical deposition (Figure 3), but SKB is also investigating the possibility of changing to horizontal deposition later on. The development work being done on horizontal deposition shows that the method is interesting and promising, but more research and development is required before it can be considered available.

Constructing the Äspö Hard Rock Laboratory

Much of the research and development for the final disposal of spent nuclear fuel has to be done in a realistic setting and on a full scale. For this reason, SKB has constructed the underground Äspö Hard Rock Laboratory (Äspö HRL) on the island of Äspö, north of the Oskarshamn nuclear power plant on the southeast coast of Sweden. Built during 1990–1995, the main tunnel descends in two spiral turns to a depth of 460 m. The various experiments are conducted in niches in the short tunnels that branch out from the main tunnel (Figure 4). The laboratory is used to investi-

114

gate how the barriers in the final repository for spent nuclear fuel (canister, buffer, backfill, closure and rock) prevent the radionuclides in the fuel from reaching the ground surface. Another important purpose is to develop and demonstrate methods for building and operating the final repository. One example of this is the investigation of the excavation damage zone (EDZ) around tunnels. In the 1970s, the zone was known to develop, but its possibilities to transport radionuclides up to major fracture systems in contact with the ground surface was only vaguely understood. Consequently, the canister was conservatively decided to be placed outside of this zone in a borehole below the tunnel floor – KBS-3V. Today, the knowledge of the properties of the EDZ has risen to a level that theoretically makes it possible to design tunneling so that the EDZ plays a secondary role as a conduit for groundwater transport and transport of radionuclides, even in a drill-and-blast tunnel. Atlas Copco drill rigs have been used for the excavation work at Äspö HRL due to their ability to drill holes with great precision, in particular the tunnel contour holes. The charges were carefully calculated, placed and detonated with accurate initiation sequences. A 1.5 m high, 8 m long and 0.5 m deep rock block was excavated from the tunnel wall by wire sawing. This block was



Horizontal Deposition RNR Experiment True Block Scale Sealing of Tunnel at Great Depth Backfill and Plug Test Deposition Machine Test

Alternative Buffer Materials

Prototype Repository

Minican

Pillar Stability Experiment

BRIE

Lot

Canister Retrieval Test

Microbe Projects

TBT

Dome Plug Project

Lasgit Sulphide Experiments

Matrix Fluid Chemistry Experiment

LTDE Caps - Counterforce Applied to Prevent Spalling Swiw Experiment Expansion of Äspö HRL 2011–2012

Colloid Project

Concrete and Clay

True-1

Courtesy of SKB, Illustrator: Jan Rojmar

Figure 4: The Äspö Hard Rock Laboratory (HRL) is a research facility in Sweden where field experiments and rehearsals are held for the final repository of spent nuclear fuel.

then cut into 100–110 mm thick slabs, which were mapped for fractures and hydraulic connectivity. Fracture occurrence was visualized as seen in Figure 5. Two major theses could now be verified: careful drilling, charging and blasting limits the development of new fractures in the rock wall and floor and thus new hydraulic transport paths around the tunnel. In addition, it was verified that new fractures from different rounds are not connected due to the lateral offset between the hole bottom of a round and the hole start of the next round. Furthermore, the first part of a round is uncharged, making the distance larger than the extent of the blast-induced fractures. All of the KBS-3 method’s subsystems are available in the Äspö HRL for demonstration in a realistic setting, and many different countries and organizations are participating in the experiments. In the future, the facility will be used to train the personnel who will work in the final repository at Forsmark. Moreover, SKB permits external parties to carry out their own specific experiments and tests in the Äspö HRL in both the nuclear area as well as in conventional engineering fields.

Sweden’s nuclear power companies are obliged to pay the costs of the measures needed to manage and dispose of

Figure 5: A visualization of natural (red) and blast induced (green) fractures in a block cut into slabs. Contour holes are marked in gray.

the nuclear waste and to decommission the facilities. This includes the costs for management and disposal of the operational waste as well as a fee to a special fund, the Nuclear Waste Fund, as a contribution to the cost of the rest of the country’s nuclear waste program and future decommissioning of the nuclear power plants. The size of the fee is determined by the Swedish Government. ◙


115


Financing

Courtesy of SKB

Regulating air flows is a key consideration in all construction projects.

A smarter way to ventilate Fresh air and ventilation systems are indispensible in tunnel construction and are notorious for being major consumers of high-cost energy. Today’s systems are a good deal smarter. Few people think about ventilation as they go about their daily lives in our modern society. The fact that our offices, department stores, schools, museums, cinemas and so on are all well ventilated is something we take for granted. Below ground, however, it’s a completely different story. Here, ventilation is critical – and can never be taken for granted. Without proper ventilation, human beings cannot survive below the Earth’s surface and excavation work of any kind is simply impossible. Tunneling engineers depend on a constant supply of fresh air and ventilation in order to do their jobs. They need oxygen to breathe and ventilation for evacuating contaminated air, such as ground gases, dust from excavation, emissions from diesel driven equipment and, not least, the toxic fumes generated

116

by blasting. Research shows that although many ventilation systems do meet local health and safety standards, they often end up as being one of the biggest items on the project cost calculation sheet due to a high level of wastage, with fans running at 100% output frequency, and the spiralling cost of powering such systems. Fortunately, this is about to become a thing of the past. Many tunneling projects still use outdated ventilation systems that are inefficient, consuming excessive amounts of energy and thereby burdening the economy of the entire project. However, over the last few years, systems designers have recognized this dilemma and a number of interesting solutions have begun to emerge. These solutions have two things in common. They must be flexible in order to suit the widest


VENTILATION SYSTEMS: OPTIMIZING THE AIR FLOW

Atlas Copco offers a flexible ventilation system featuring high pressure fans and ducting that delivers air along extensive lengths, with a capacity of up to 200 m 3/s.

variety of tunnel requirements, in terms of tunnel length and design. They also must be optimized to adjust the air flows to each activity, such as drilling, blasting and hauling, in order to eliminate wastage and keep running costs to a minimum without compromising on safety. Supplying the right amount of fresh air to the right place, at the right time is not a simple task. Among the parameters that have to be taken into consideration in designing such a system are the types of tunnels being constructed, tunnel dimensions and length; the type and number of equipment that will be in use, such as drill rigs, loaders and haulage trucks; the number of personnel; the energy source; and the cost of powering the system.

In the main, older systems cannot be adjusted in this way and simply run at 100% of their capacity all the time, driving more fresh air into the tunnel than is needed and extracting air when there are no gases or fumes to extract. Furthermore, they normally leak substantial amounts of air along the way which reduces pressure and increases energy consumption which drives up the overall costs. In general, the maximum ventilation frequency is required only during intensive haulage and after blasting at the most distant sections of the tunnel.

Ventilation on demand

Today’s ventilation systems have individual components – fans and ducting – which are made from robust, top-class materials, specifically designed to cope with the demands of the tunneling environment and usually come with some form of control facility. This capability, which is often referred to


117

Tunneling Technique

A modern ventilation system is based on three main components: • Fan station – high pressure fans, silencers, mounting and starters • Flexible ducting – tubes that distribute the fresh air and dilute exhaust gases. These often come in a variety of sizes and lengths and in different material combinations • System design – calculations aimed at optimizing the air flow for a given project considering the various construc tion stages Compared to most industrial applications, the ventilation systems required for tunneling present a range of different and

often complex challenges. Drilling operations, for example, normally require a 30–40% ventilation capacity, whereas mucking and haulage will require significantly more. In other words, ventilation needs to vary during the excavation cycle and depends on the type of operation being performed at any given time, at any given stage of construction.


Optimized air flow

Atlas Copco offers a comprehensive range of high-pressure ventilation systems with fans and ducting that direct the right amount of air to the production area. An increasing number of mobile tunneling equipment is equipped with WiFi transmitters. These can be synchronized with the frequency inverter that enables the presence of vehicles, their type and work activity to be identified by the ventilation system, which then allocates the required air flow accordingly.

100%

50%

99%

1%

Figure 1: If ventilation ducts are not installed correctly, leakage of air from creases and holes will increase the required fan frequency.

as “ventilation on demand”, is the most effective and costefficient way of dealing with ventilation underground and give tunnel managers the freedom to tailor the supply of ventilation in accordance with the needs of the operation on a day-to-day or even shift-to-shift basis. On demand ventilation gives: • Air flow tailored to the needs of equipment or activity • Local adaptability • Reduced energy costs • Minimized energy waste

118

By using a frequency inverter, the speed of the fan will not be higher than necessary and the air flow during excavation will be optimized, increasing, for example, directly after a blast to evacuate the fumes as soon as possible, and then reverting to normal running mode. The potential savings on energy and costs from using the Atlas Copco ventilation system are considerable, possibly as much as 50 % compared with some traditional ventilation systems, as shown in Figure 2. In addition to its high quality materials, flexible ducting, low noise and control functions, the system also provides an extensive range of components that give the tunnel planner the opportunity to create different combinations for a variety of different tunneling scenarios. Atlas Copco’s ventilation system range includes high pressure fan stations that can deliver air along extensive lengths of ducting in different diameters with a capacity of up to 200 m 3/s. Even more important is that the system also offers highly efficient impeller blades with variable angles which can be set up in series during production. The possibility to simply adjust the pitch of the blade angle makes it simple and quick to adapt the fans to suit different motor dimensions and pressure requirements. With a nonadjustable impeller, we would need as many impellers as there are motors for each given diameter. To solve this problem, Atlas Copco has equipped the impellers with adjustable blades and the company's technicians also carry out static and dynamic balancing of each impeller on site before use. While quality components and flexible design are in high demand, a major plus point in favor of Atlas Copco’s solution is the fact that it comes with a comprehensive design, installation and service package including project monitoring. To illustrate the need for professional installation, just a small increase in leakage from 0.3%–1% can potentially double the required fan frequency (see Figure 1). Eliminating wastage should, therefore, be of top priority to project managers and engineers when ventilation systems are installed.

Flexible ducting

Ducting has one purpose – to get the air from the fan station to the tunnel face where excavation is taking place. The ducting, which consists of PVC-coated fabric, must be light and strong, and easy to mount, replace and remove. Although



Energy output (kWh)

100%

Blasting

Blasting

Mucking and Haulage

Mucking and Haulage

Scaling Concrete spraying

50% Bolting Drilling

Bolting Drilling

Average total energy savings 0%

Scaling Concrete spraying

30–50% (minimum)

Atlas Copco variable frequency system

Tunneling activity

Figure 2: Variable frequency is an essential feature of Atlas Copco's ventilation system. It enables the output frequency to be adapted to each activity, which results in substantial energy savings of 30–50%.

large-diameter ducting equates with good ventilation, a rule of thumb is that the larger the diameter is, the greater the risk of damage will be. A damaged duct loses its function rapidly due to the pressure drop and is easy to tear if it is too large for the tunnel. In order to optimize both the investment and the running cost it is essential to choose the right equipment combination. This is most important when choosing the size of the ducting. A larger duct reduces the risk of pressure loss, which, in turn, lowers the fan investment as well as the running cost.

Future development

Together, these advantages enable a multitude of solutions to be constructed for different requirements and the air flow to be optimized for each application, leading to a low overall running cost. The possibility to easily regulate ventilation fans from a central control point is likely to advance the technology even further. Since the cost of ventilation is a major item for tunnel excavations – often accounting for some 35–45% of the total energy consumption – it is an area that is ripe for modernization with huge potential gains for civil engineering projects as well as the engineers who carry them out. ◙


119

Tunneling Technique

But it’s not that simple. How can a large-diameter duct be installed in a hydropower tunnel, for example, if all of the available space is taken up by other installations, or where the size of the tunnel cross section is so limited that a large duct will obstruct machinery and disturb the excavation sequence? The solution is to be able to select from a range of fan stations and ducting, not only in terms of diameters, but also in terms

of the amount of pressure required. In addition, it should be possible to install one or more ducts in parallel.

High productivity and good drill steel economy are essential aspects when choosing the right drilling equipment. The Atlas Copco COP 3038 hydraulic rock drill, designed for the hole range 43–64 mm, is a popular choice among tunnelers for face drilling.

High precision drilling

for great tunneling results

Total control of the drilling process, from rock formation analysis to percussion pressure and hole deviation, is the most crucial factor on the road to high quality and profitable tunnel construction. In order for a tunneling project to be completed successfully – on time, on budget and profitably – it is not only essential to have a thorough understanding of all excavation procedures, but also how the various activities affect one another. Experience shows that quality and profitability can only be achieved when all activities in the excavation cycle are carefully controlled. The reason for this is that each activity in the tunneling chain affects other aspects of the work in one way or another. For example, poor scaling reduces safety during drilling; careless

120

charging has an adverse affect on the damage zone and, therefore, mucking efficiency, and so on. Of all the techniques needed for tunnel construction, the drilling process is the most crucial – and the most important one to control. Why? Because poor drilling and blasting limits the pull of the rounds; more rock reinforcement will be required due to the damage caused to the rock mass; scaling and mucking will take more time; more concrete for lining work will be required due to overbreak; and the quality of the grouting will be more difficult to define. These are just a


HIGH PRECISION DRILLING

2

3

4

1

1. Feed force, 2. Piston impact force, 3. Rotation, 4. Flushing

Figure 1: The principle of tophammer drilling. This method is usually employed in medium to hard rock formations.

few of the “knock-on” effects that are both quality and costrelated. Irrespective of whether the project is located in the countryside or in an urban area, or if it is a tunnel for a hydro power plant, or for infrastructure such as railways or roads, high precision drilling is required for blasting, pre-grouting, probe holes, spiling and more.

Another risk factor is that the spacing between the contour holes becomes too great. This will damage the rock supporting the contour, meaning that “smooth blasting” is not achieved. In other words, the full capacity of the smooth blasting technique is highly dependent on precision drilling. .

In urban areas, underground blasting often causes problems of vibration, especially when the tunnel being excavated is located close to an existing tunnel construction, surface buildings, and other sensitive structures. To be able to blast in hard, competent rock in sensitive areas, the amount of explosives must be calculated for vibration limitations and be adjusted for the contour.

Theory of percussive drilling

Vibrations in urban areas can have a significant impact on the feasibility and successful completion of the project. In such cases, precision drilling is paramount as the margin for error is minimal when drilling blastholes. Precise location is also of great importance for injection grouting holes and bolt holes.

Pressure is built up inside the rock drill, which, when released, drives the piston forward. The piston strikes the shank adapter, and the kinetic energy of the piston is converted into a stress wave that travels through the drillstring to the hole bottom (see Figure 1). In order to obtain the best drilling economy, the transmission of energy – from rock drill to drill steel to rock – must work smoothly, which means that all the components of the drillstring must be well-tuned and operate in harmony. The higher the percussion pressure, the higher the speed of the piston and, consequently, the energy. When the bit maintains good contact with hard and competent rock, the shock wave


121

Tunneling Technique

The contour also needs to be created with utmost care and as near the planned contour as possible. If deviation on the contour holes is too great, the blasted tunnel may exceed its planned dimensions and, in turn, make the remaining pillar between the next tunnel, or an existing tunnel, too small – thereby jeopardizing stability.

One of the first priorities when striving for accuracy is to understand the theory of percussive drilling. Percussive drilling breaks rock by delivering hammer blows to a drill bit at the hole. The energy required to break the rock is generated by a pneumatic or hydraulic tophammer rock drill.


s

Reflecting wave

energy is utilized to its maximum. Conversely, where the contact between the bit and the rock is poor, the energy is unable to leave the drillstring and instead reverses back up the drillstring as a tensile wave (see Figure 2). It is only when drilling in sufficiently hard rock that the maximum amount of energy per blow can be utilized, and without sufficient energy in hard rock, there will be a compressive wave sent back through the drillstring. In soft rock, to reduce the reflected energy, the percussion pressure, and thus the energy, will have to be lowered (see Figure 3).

+ –

Primary wave Figure 2: Poor contact between bit and rock results in poor efficiency.

For any given percussion pressure, the amplitude and, therefore, the stress in the drill steel will be higher the lower the cross section is of the drill rods. To get the longest possible service life from shank adapters and rods, it is important to ensure that the working pressure is matched to the drillstring at all times.

Energy losses

Precussion pressure

For every additional coupling, a shock wave loses 3–5% of its energy as it travels down the drillstring. This loss is partly due to the difference in cross-sectional area between the rod and the sleeve and partly due to imperfect contact between the rod faces. The rule of thumb is the poorer the contact, the greater the energy loss.

Soft rock

Hard rock

Figure 3: To reduce reflected energy, percussion pressure is lowered.

When the shock wave reaches the bit, it is forced against the rock and crushes it. However, the efficiency at the bit end never reaches 100% because some of the energy is reflected as a tensile pulse or compressive pulse. In this case, the poorer the contact between bit and rock, the poorer the efficiency. Therefore, to optimize drilling economy, the parameters of percussion pressure, feed force, and rotation must all be harmonized. A professional driller knows how to approach this task and utilize his/her equipment, including the drill steel, with the best possible efficiency.

Feeding

Feed force and rotation

The purpose of the feed force is to ensure that the drill bit maintains good contact with the rock at all times. However, the bit must still be able to rotate, and this means that the feed force must always be matched to the percussion pressure (see Figure 4).

Low percussion pressure

High percussion pressure

Figure 4: Feed force must be matched to percussion pressure.

122

The purpose of rotation is to turn the drill bit to a suitable new position in preparation for the next blow, which should occur on fresh rock for maximum effectiveness. Using button bits, the periphery is turned about the same diameter of the gauge button between blows. Additionally, the rotation rate is increased using a higher impact frequency and reduced bit diameter. Using insert bits, it is recommended that the rotation rate be increased by 25%.



Figure 5: Face drilling rigs are used for a variety of applications in tunneling, including blasthole drilling, bolthole drilling, grouthole drilling and drilling for pipe roofing or spiling. Each application has its own requirements for precision and accuracy.

Flushing the hole

The drill cuttings are removed by blowing air or water into the bottom of the hole. This is known as flushing. As the power output from the rock drill increases, accompanied by increased penetration rate, efficient flushing becomes gradually more important. The flushing medium is normally air for surface drilling and water for underground drilling. The required flushing speed depends on: • Specific gravity: Higher specific gravity calls for a higher flushing speed. • Particle size: The larger the particles obtained in breaking the rock, the higher will be the necessary flushing speed will be.

Tunnel excavation involves a great many applications that require precision drilling – from blastholes, rock bolting and grouting to spiling, meshing and more (see Figure 5) – and each application has its own specific requirements for precision and accuracy. For example, in blasthole drilling it is crucial to minimize deviation as any digression from the theoretical line in excavating the tunnel will incur far greater construction costs. Drilling has a direct impact on pull of the round in blasting, and if good control and minimal deviation are achieved, typically no greater than 1.5%, a better blasting result can be expected. If drilling quality is kept to a high standard, precision can also be applied to charge calculations and the firing pattern. This results in longer pull of the round, and reduced vibration. The overall aim is to follow the drill plan as closely as possible when producing parallel blastholes. As the blast effect


123

Tunneling Technique

• Particle shape: The more equilateral the particles are, the greater will be the necessary flushing speed. To illustrate this, it is easy to carry away a particle in the shape of a leaf than one of the same weight which is spherical.

Blastholes and contour


Figure 6: The look-out angle is the angle between the drilled profile (practical line) and the theoretical profile. If the look-out angle is incorrect, there will be either overbreak or underbreak which means uneconomical drilling results.

is calculated with a certain distance between all the holes, it is important to achieve identical spacing between them. If deviation has occurred and the spacing is too short or burden too large, the blast effect will be too great, resulting in vibrations, short pull and a damaging impact on surrounding rock. In order to avoid overbreak in blasting, the aim should be to reduce the look-out angle as much as possible and still have enough room to drill the next round (see Figure 6). Overbreak is costly in terms of haulage of excess rock but even more so if a tunnel lining is required, in which case the overbreak will need to be replaced by concrete. However, the space created by the look-out angle is needed in order to provide space for the rock drill in the next round.

Rock reinforcement

There are two kinds of rock support used in tunneling – temporary and permanent. Temporary reinforcement enables the tunneler to advance safely through weak ground and can include bolting, spiling or pipe roofing and sprayed concrete. This is followed by a permanent reinforcement system that often includes bolting and sprayed concrete (shotcrete) and sometimes concrete lining. To ensure that the permanent rock reinforcement installation will meet the requirements of the project, it is important to know exactly where to drill. It is important to follow the predesign pattern and to avoid disruption of rock reinforcement elements that may already be in place and covered by sprayed concrete.

124

Pre-grouting

The purpose of pre-grouting is to primarily seal the rock mass ahead of the face and to stabilize it to some degree. The sealing method used depends on the project and its requirements, for example, in order to stabilize the rock mass ahead or to prevent the excavation work from affecting the water table. The key factor when grouting is to be able to determine precisely where the hole should be located, especially the hole bottom. This can only be accomplished using advanced, high-precision drilling equipment.

Probe drilling

Probe drilling is required for a variety of reasons, such as to define and forecast rock quality around and beyond the tunnel face, to identify water ingress or locate different rock strata. In this case, with available knowledge of the location of the drill hole and the logged drilling data, a forecast can be made on the rock mass and water ingress. This applies to the rock surrounding the drilled hole and between other drilled holes. Manual examples of data collected from probe holes are the color of flushing water, the quality of cuttings, rock hardness, rock fracturing and water leakage. More sophisticated tools include rock formation analysis utilizing the Measure While Drilling (MWD) system.

Positioning the drill rig

There are several different ways of getting set up for drilling, and most of these are still performed manually. The manual setup technique is highly accurate when collaring a hole, but



A Boomer E2 C working at the construction site of the 4.4 km long Goetschka highway tunnel in Austria.

it is also extremely time-consuming and difficult to establish precise alignment of the feed. For high precision hole navigation, manufacturers such as Atlas Copco provide two options: navigation by aligning the feed with the aid of a laser beam or using the system Total Station Navigation. Laser navigation gives an accuracy of within 20 cm of the collaring position, provided the rig is well calibrated, and the operator aligns the feed with the laser correctly. The Total Station Navigation method gives superior precision, navigating the feed to an accuracy that is better than 1 cm if the rig is properly calibrated. Navigation is performed with fixed prisms mounted on the rig and on the tunnel walls, which minimizes human error. This system is particularly useful on curves and cross passes.

Faulty collaring and alignment

The benefits yielded by RCS are substantial for all equipment where the system is employed, not least when it comes

• ABC Regular – this level offers semi-automatic drilling. With the help of a predetermined drill plan transferred to the rig’s display, the operator can position and direct the feed for precise drilling. Drill plans and other data are generated by the site office using the Underground Manager software, see chapter "Data management tools" on p. 138. • ABC Total – fully automated execution of a complete drill round according to the drill plan with sequences pre pared using the Underground Manager. Apart from moni toring the process, the operator can use speed buttons on the rig’s display to switch between manual, semi automatic and fully-automatic positioning and drilling as required.

Minimizing deflection

To minimize deflection in the drill hole, the right type of drilling equipment must be selected, and the settings on the rock drill must be correct. This requires that the drill steel used is as rigid as possible to avoid bending in the feed and in the hole during drilling. A good guide, when it comes to blasthole drilling, is to use a 45–48 mm drill bit and a 39 mm round drill rod. This combination will leave a small space


125

Tunneling Technique

To obtain a good drilling result, it is essential that collaring the hole and the alignment of the drill rig are properly executed. To enable fast collaring and prevent misalignment, Atlas Copco drill rigs are equipped with the ABC system (Advance Boom Control), which makes it easy for the operator to follow the pre-designed drill pattern shown on the rig’s display screen. The ABC system is a part of the overall control system used on Atlas Copco equipment, called RCS (Rig Control System).

to high-precision drilling. For optimal drilling results, the Advanced Boom Control system is available with three levels of automation. • ABC Basic – the simplest form of automation. The operator controls the maneuvering of boom and feed, as well as directing the feed to the borehole position based on data displayed on the control panel.


The rock drill must have the right settings to enable smooth drilling for the first few meters and to cleanly penetrate fault zones and cracks, as well as have a good anti-jamming system. The correct rock drill settings are controlled by the RCS system.

Drill hole deviation

In order to drill with high precision, there are a number of variables that have to be taken into consideration. If one of these variables fails, it will result in deviation; i.e., the hole will not follow its planned direction or route, as illustrated in Figure 7. The structure or formation of the rock also has a major effect on hole deviation. Even if everything is done correctly when it comes to the drilling equipment – the right rock drill settings, a well-trained operator, etc. – considerable hole deviation may still occur due to the structure of the rock, especially in long hole drilling. In this case, deviation can only be minimized – not eliminated – by using the right drilling equipment and settings.

Automated rod handling

Adding new drill rods to the rock drill’s feeder is today an easy task thanks to modern rod handling systems, which automate the process. The use of mechanized rod handling systems is especially effective for extension drilling of extra long holes in drifts and tunnels. These systems enable the drilling of longer rounds, deeper holes for cement injection around the tunnel profile, and long bolt holes in confined spaces. They also allow the rigs to be used for exploratory drilling ahead of the face. The entire process is controlled from the operator panel, eliminating all heavy and dangerous aspects of manual rod changes. At the press of a button, one rod is simply added after another with a typical magazine capacity of 10 drill rods.

Figure 7: Hole deviation is of crucial importance as it impacts directly on blasting and the tunnel profile. Deviation may be a result of poor positioning, alignment of feed, a structural problem with the rock or incorrect settings on the drill rig such as too high feed force.

between the drill hole wall and the drill steel, enough to prevent bending but still large enough for flushing out the cuttings. In long hole drilling, the first rod should be a rigid guide tube for the same reason as in blasthole drilling. To be able to drill straight holes, the first 2–3 m are the most important because this provides a guide for the rest of the hole. In addition, straightness is assisted by keeping the feed firmly against the face during drilling, preventing it from sliding.

126

Safety and increased productivity are two main benefits of automated rod handling. Compared with the traditional, manual methods of adding drill rods, an automated rod handling system means people do not have to stand in the basket and be exposed to falling rock or moving machine parts or to manually handle heavy extension rods. Furthermore, it has been calculated that productivity is boosted by 40%.

Drilling tools

As button bits dominate 95% of face drilling applications, they should be the first choice. It is only in very special conditions that insert bits will be the better choice. Moreover, results have shown that bits with ballistic buttons outperform bits with spherical buttons in terms of penetration rate and, in some cases, also offer better service life and longer grinding intervals. Although buttons bits are preferred, rock conditions will also influence this choice.



For drifting and tunneling, two types of drill rods can be chosen. Standard drifter rods have male threads at both ends. Speedrods from Atlas Copco Secoroc have a male thread at the front end and an integrated coupling with a female thread at the shank end. Both rod types are carburized, which means that all surfaces, including the inside of the flushing hole, are hardened.

Drill bits Ballistic button bit Recommended for medium to hard rock formations. This type of bit gives higher penetration rates and longer grinding intervals compared with spherical button bits.

The Magnum SR conical thread system, unique and patented by Atlas Copco Secoroc, is adapted to the new and powerful generation of hydraulic rock drills. The conical thread shape offers more material at the rod end. Straighter holes and a much longer service life are two of the results of the SR system. Moreover, Magnum SR bits are easy to uncouple, allowing faster changes and more holes drilled.

Spherical button bit Should be used in hard and abrasive rock formations. A bit with spherical but tons is stronger and more wear resistant in this type of rock compared with a bit with ballistic buttons.

The carburization gives better wear resistance and a higher fatigue strength compared to an induction-hardened rod. Standard drifter rods, as well as Speedrods from Atlas Copco Secoroc, are produced with either a hexagonal or a round rod section. For a given hole size, the largest possible rod cross section should be chosen to match the required hole size and the rock drill in order to achieve the best possible service life, hole straightness and penetration rate. The long middle section of the drifter rod is generally hexagonal, with a 32 mm or 35 mm cross section. Round, 39 mm rods are getting more and more common, especially for hole lengths of 4 m or longer. The bit end of the rod is slimmer and has a smaller thread in order to fit the small bits and hole sizes used.

Ideal for extremely abrasive rock formations or in soft rock formations that cause "snake skin" problems on buttons. Produces straight holes but has lower penetration rates than button bits .

Reaming bit Dome reaming bit Used to drill the opening holes for a blasting round in a tunnel. An alternative bit to traditional reaming equipment. This bit should be used in a pre-drilled hole.

Drift rods

Using the round rod, the flushing properties for clearing the cuttings out of the hole are not as good as with the hexagonal rod. This can result in a higher risk of jamming round rods when drilling in fractured rock formations, mainly when drilling 45 mm holes or smaller. In homogeneous rock, this is normally not a problem.

Round standard drifter rod Drifter rod used together with separate coupling. The advantage of using a separate coupling is that it can be easily replaced separately, without changing the rod, if the coupling is worn-out or damaged.

L

Round Speedrod (Magnum SR) 39 mm Drifter rod with an integrated coupling. The advantage with these rods is that they have better energy transmission, approx. 3-6% higher compared to standard drifter rods with separate couplings. The round Speedrods are also stiffer compared with a hex Speedrod and give better hole straightness in difficult rock formations.

L

Hexagonal Speedrod (Magnum SR) 39 mm Drifter rod with an integrated coupling. The advantage of these rods is that they achieve better energy transmission, approx. 3-6% greater compared to standard drifter rods with a separate coupling. In addition, the hex Speedrods are manufactured with less material than the round Speedrods, which makes them both lighter and more flexible.


127

Tunneling Technique

In drifting and tunneling operations, it is always necessary to make an opening in the tunnel face to provide expansion space for the rock when blasting out the complete round. The most common method is the parallel hole cut. Cut hole drilling of the large center hole, or holes, is usually carried out by reaming, which first requires the drilling of a pilot hole with the ordinary blasthole drill bit. The pilot hole is then reamed from actual hole size to 64 mm–127 mm.

L

ØD

Hexagonal rods are today’s standard, while round rods, 39 mm in diameter, are becoming increasingly more common. The round rod is stiffer, because of more material in the crosssection. Round rods give straighter holes and are, therefore, recommended when hole deviation is a problem.

ØD

Hexagonal vs. round rod

Reaming equipment

Insert bit


Grinding interval drill meters

10 regrindings per drill bit

60

50

40

30

20

10

0

Total bit life Drill meters 100

200

300

400

500

600

700

Figure 8: Typical bit life grinding at different intervals. The Atlas Copco Secoroc Grind Matic BQ3 grinding machine can handle drill bits up to 127 mm in diameter.

Note that the stress level on the rod will increase with increased cut hole size. This can lead to premature thread wear or rod breakage. Reaming can be carried out using either a traditional pilot adapter with a reaming bit or the new Secoroc dome bit. The dome bit offers a shorter total time for drilling of the cut hole compared to conventional reaming equipment. Due to the reverse flushing on the dome bit, stress levels on the drill string, rock drill and drill rig are reduced when withdrawing the bit from the hole. The task of the shank adapter is to transmit rotation torque, feed force, impact energy, and flushing medium. It is made from specially selected material to withstand the transmission of impact energy and rotation from the rock drill to the drillstring, and it is hardened through carburizing.

Bit service life

It is a well-established fact that the service life of a button bit increases considerably if the cemented carbide buttons are ground. Nowadays, it has become extremely important to grind button bits at proper intervals to extend the service life of the rock drilling tool, maintain penetration rates and costs, and drill straight holes.

128

With so many parameters involved, it is difficult to estimate bit service life. First, a proper grinding interval must be established, preferably at the stage when the button has a wear flat of one third of the button diameter. When the number of drilled meters to reach this stage has been established, then the calculation of bit life can be made by multiplying the number of times it can be reground. As a general rule, a bit can be reground 10 times; smaller bits may achieve slightly less than this figure, while larger bits may achieve more. So, if the grinding interval has been established as 60 drill meters, then the average bit life will be 660 drill meters (see Figure 8). If a bit is overdrilled and the wear flat is more than half of the button diameter, there is a tendency towards cracked buttons. There is always a sharp edge created on the button, and this becomes sharper the more the bit is overdrilled. This sharp edge, especially on ballistic buttons, is very brittle. Once the edge cracks, pieces of cemented carbide break away and circulate in the hole, causing secondary damage to the buttons. When a bit doesn’t show any visible wear flat, it may be suffering from micro cracks on the cemented carbide surface.



100%

Button damage risk

100%

Penetration rate

Soft rock 75%

75%

Hard rock 50%

50%

Hard rock 25%

25%

Soft rock 0% Button wear flat

1/3 flat

1/2 flat

2/3 flat

0%

Button wear flat

1/3 flat

1/2 flat

2/3 flat

Figure 9, left: Risk of total loss when a bit is overdrilled. Figure 10, right: Penetration rate drops as the button profiles flatten.

This is known colloquially as snake skin and can be clearly seen when using a magnifier. In this case, the surface has to be ground away; otherwise the micro cracks lead to more severe damage on the buttons. Likewise, buttons that protrude too much must be ground down to avoid damage, as shown in Figure 9.

wear flat after just 10–20 drill meters accompanied by a small drop in penetration rate. When it has a wear flat equivalent to one-third of the button diameter, the penetration will have dropped by 5%. If the bit is used further until it has a twothirds wear flat, the penetration will have dropped more than 30% (see Figure 10).

In all rock excavation operations, the cost is usually expressed in cost per drilled meter (cost/dm), in cost per cubic meter (cost/m³), or in cost per tonne (cost/t). The cost to produce a hole depends on how fast it can be drilled and how many tools will be consumed. The cost to produce a cubic meter of rock is dependent upon the cost of the hole and the cost of blasting.

When a bit has a heavy wear flat, it tends to deviate, and by the time it reaches the bottom of the hole, it will have deviated far more than planned. As a result, the blast will produce short pull. In contour hole drilling, it is of utmost importance that the holes are straight. If the holes deviate, the tunnel walls will be uneven, which increases the risk for overbreak or underbreak.

If the blasthole is of poor quality, then more explosives will be consumed in blasting the rock. Worn bits very often give a poor quality hole with a greater risk of deviation.

Penetration Rate


129

Tunneling Technique

When the right bit has been chosen for the rock condition, it will provide maximum penetration rate along with acceptable hole straightness. In rock conditions like Swedish granite with a compressive strength of around 200 MPa, the bit gets a

Rock formations with different layers and joints are often characterized by heavy hole deviation, putting extra stress on the remaining rock tools in the drill string. A sharp bit always cuts better and will prevent both deviation – and its disadvantages. ◙

Using emulsion bulk explosives that are string loaded is a typical technique in the smooth blasting method.

Quality holes for safe and efficient blasting When it comes to blasting for tunnel construction, control is paramount. From drilling through to charging and detonation, it requires a careful, step-by-step procedure. Since Alfred Nobel invented dynamite in 1866, explosives have played a major role in tunnel construction all over the world. Suddenly, it was possible for men to blast their way through mountains easier and safer than ever before, thereby rapidly expanding the development of infrastructure and revolutionizing travel, commerce and communications.

Nowadays, blasting tunnels is an exact science, practiced by highly skilled specialists using modern technology and great care to ensure that the task is carried out in the safest possible way.

However, despite the fact that Nobel’s invention was a vast improvement on the volatility of black powder and nitroglycerine, the widespread use of dynamite still came at a heavy price. Ignorance and carelessness led to many injuries and fatalities.

At its most basic level, blasting involves the use of explosives inside drilled holes to displace rock mass in a predetermined size and volume. But in order to meet today’s strict demands for safety and efficiency, it is the straightness and quality of the blasthole that is the key to success. The lower the quality

130

Quality holes are key


CHARGING AND BLASTING

of the hole, the more difficult it is to meet these demands and, just as important, the harder it becomes to calculate the volume of the rounds and the desired rock fragmentation. In this respect, the 1970s proved to be a turning point as hydraulic drill rigs began to replace pneumatic equipment, resulting in considerably increased blasthole quality. Simultaneously, blasting technology also took a leap forward with innovations such as ANFO (Ammonium Nitrate and Fuel Oil), a bulk explosive that could be blown into the hole by high pressure air. Not surprisingly, this method became hugely popular and was soon followed by the modern emulsions and slurries that we now see being used worldwide. Today, computerized systems are also commonly employed for calculating charges and drilling patterns, and this has also made a vast improvement to blasting precision. At the same time, it is a rule of thumb that no amount of precision in charging and blasting can make up for poorly executed drilling.

Control at every step

To uphold modern standards of safety, speed and accuracy, quality must be maintained at every step in the blasting process – and there is little margin for error. A well-charged drill hole is defined by the success of the drilling because all decisions made during that stage will have a profound impact on the blasting operation as a whole. Charging of the holes, the next step, can be carried out relatively quickly, either manually using plastic/paper charges or, in the case of bulk explosives, with mechanized charging equipment such as trucks featuring charging baskets, hose reels, hydraulic support legs and onboard compressors. The most common explosives used for charging blastholes today are: • Cartridge • Bulk – ANFO – Emulsion The various explosives in cartridges, known as packaged explosives, are made up of nitroglycerine, nitroglycol, watergel or emulsion-based products. These typically include paper cartridges, plastic hoses and plastic pipes. Bulk emulsion explosives are composed of very small and dense droplets of ammonium nitrate solutions and other oxidizers enclosed by a mixture of mineral oil and wax, called matrix. At this stage, the product is only an oxidized substance.

The ANFO receptacle on Atlas Copco Chargetec UV2, a single boom truck that enables optimized ANFO or Emulsion charging of a full drill pattern.


131

Tunneling Technique

To turn the matrix into an explosive, it must be sensitized by adding a fumigant immediately in front of the charging hose. During the pumping of the matrix to the blasthole, a gassing agent is added and a chemical reaction begins. The development of gas bubbles in the matrix results in an increment of


the volume at the same time as the density decreases. The gas bubbles act as “hot spots” in the explosive, carrying the detonation through the explosives string. Due to the oil/wax packing of the ammonium nitrate, it is not sensitive to water. Its strength can be controlled by changing the weight of the blasting agent per meter blasthole. This can be achieved by varying the retraction speed of the charging hose. The hose speed and pumping flow are controlled using the charging truck’s computer system.

S

ANFO is just as powerful as dynamite but far less hazardous and more economical. It is, however, very sensitive to water and cannot match the versatility and safety of modern emulsion explosives, which are today the most commonly used blasting agents.

B

Whatever method of charging and blasting is used, the important thing is to always dimension the size of the charges correctly. This will have a direct impact on the rock fragmentation achieved in the blast, on whether or not remaining rock is damaged, and whether vibrations affecting the surrounding environment are kept within acceptable levels.

Recent developments

Since pneumatics gave way to hydraulics more than a quarter of a century ago, the capacity of blasthole drill rigs has increased considerably. The focus here has not just been on speed but also on the quality of drilling. The definition of quality applies when all rock characteristics, project demands and basic drilling parameters, such as hole location, straightness and length, percussion pressure, applied torque and feed force, are taken into account. In recent years, explosives have also become much easier and safer to use. For example, improved fumes characteristics in emulsions that are oxygen-balanced generate a minimum of noxious fumes and far less smoke. The development of non-electric initiating systems such as NONEL, which is the most frequently used, has increased safety during blasting operations because it is not susceptible to electrical hazards. The NONEL system has also made connecting of the detonators safer and faster, and emulsion explosives have shortened the ventilation re-entry time. Electronic detonators provide a detonation interval as low as 1 ms without any interference from each other. These are not commonly used due to their relatively high price, but they are economical whenever a smooth contour is essential and when blasting in close proximity to vibration-sensitive areas. Another advantage of electronic detonators is the flexibility they provide for sequential blasting with set delays and a large span of intervals. Figure 1: The three principal stages of detonation.

132

All of the above contribute to a faster work cycle and to better quality throughout the tunneling process, from drilling,



charging, blasting, ventilation, scaling, rock support work and grouting, loading and hauling to setting up for the next blast.

One free face

Unlike bench blasting, which is carried out on two or more free surfaces, tunnel blasting is carried out toward one free face. The mobility of the blasted rock is more constrained, and a second free face has to be created toward which the rock can break. This is achieved by creating a cut or opening in the tunnel face, which is done in one of three ways – as a parallel hole cut, a V-cut, or a fan cut. After the cut has been created, blasting toward the cut can begin. The process is similar to bench blasting but requires a higher specific charge due to the need for good fragmentation and the absence of hole inclination. The blastholes surrounding the cut should be placed in an even pattern with a space/burden ratio of 1:1. The rock is affected by detonation explosives in three principal stages. In the first stage, starting from the initiation point, the blasthole expands by crushing the blasthole walls. In the second stage, compressive stress waves emanate in all directions from the blasthole with a velocity equal to the sonic wave velocity in the rock, as shown in Figure 1. When these compressive stress waves reflect against a free rock face, they cause tensile stresses in the rock mass between the blasthole and the free face. If the tensile strength of the rock is exceeded, the rock breaks in the burden area, which is the case in a correctly designed blast. In the third stage, the released gas volume enters the crack formation under high pressure, expanding the cracks. If the distance between the blasthole and the free face is correctly calculated, the rock mass between the blasthole and the free face will yield and be thrown forward.

Burn cut

One of the most commonly used cuts in tunneling today is the burn cut, or parallel hole cut. The cut holes are drilled parallel to each other. One or more are left uncharged so that a free face is created for the other holes to break into. The holes left uncharged and void are usually reamed to a larger diameter, known as reamer holes. (see Figure 2).

To obtain good forward movement and centering of the muckpile, the cut may be placed approximately in the middle of

2 10

1 2

1. Big hole 2. Blasthole with explosives

Figure 2: In the burn cut technique, typical for tunnels, all holes are drilled parallel to each other. The numbers in the illustration indicate the firing sequence.

the cross section and quite low down. This position will give less throw as well as lower explosives consumption, because of more blasting downwards. A high position of the cut gives an extended and easily loaded muckpile with higher explosives consumption and more drilling due to upwards blasting which requires greater force. 1 Big hole location of the cut is on the knee holes, the The common 2 Blast hole with explosives row of holes above the lifters (floor). The burn hole cut comprises one or more uncharged large diameter holes that are surrounded by small diameter blastholes with small burdens to the reamer holes. The first detonated hole can only blast out the volume of rock that fits in the large hole.

The larger the opening becomes, the greater is the distance between the holes. The blastholes are often drilled in squares around the opening, as shown in Figure 2, which results in a geometrically appropriate angle for extracting the rock. The number of squares in the cut is limited by the fact that the


133

Tunneling Technique

The cut may be placed at any location on the tunnel face, but its location influences the throw (trajectory), the consumption of explosives and the number of holes needed in the round. If the cut is placed close to a sidewall, there is a probability of better exploitation of the drilling pattern with fewer holes in the round. Furthermore, the cut may be placed alternately on the right or left side in relatively undisturbed rock.

10 1


burden in the last square must not exceed the burden of the stoping holes or a given charge concentration in the hole. The cut holes occupy an area of approximately 2 m².

a=1.5d

d a=1.5d Figure 3: Typical design of the reamer hole with calculated distance for blastholes.

When designing the cut, the following parameters are important for a good result: • Diameter of the reamer hole • Burden • Charge concentration In addition, drilling precision is of the utmost importance, especially for the blastholes closest to the reamer holes. The slightest deviation can cause the blasthole to meet the reamer hole or the burden to become excessively large. Too large a burden will only cause breakage or plastic deformation in the cut, resulting in a too short pull.

Hole diameter

In burn cuts, one of the parameters for good advance of the blasted round is the diameter of the reamer hole. The larger the diameter, the deeper the round may be drilled, and a greater advance can be expected. One of the most common causes of short advance is that the reamer hole is too small in relation to its depth. An advance of approximately 90–95% can be expected for a hole depth of 4 m and one reamer hole with 102 mm diameter. If several reamer holes are used, a fictitious diameter has to be calculated. The fictitious diameter of the opening may be calculated in accordance with the formula D = d √ n, where D = fictitious empty reamer hole diameter; d = diameter of empty reamer holes; n = number of holes.

2

4 6

1

3 5

2

4 6

5 3 1

In order to calculate the burden in the first square, the diameter of the reamer hole is used in the case of one reamer hole and the fictitious diameter in the case of several reamer holes. The distance between the blasthole and the reamer hole should not be greater than 1.5 times the diameter of the reamer hole for the opening to be clean blasted. If the distance is longer, there is merely breakage, and when the distance is shorter, there is a great risk that the blasthole and reamer hole will meet. However, the distance mentioned above is only a rule of thumb. The actual distance in the cut depends on the rock conditions. Therefore, the position of the blastholes in the first square is expressed as: a =1.5d where a = C—C distance between the reamer hole and the blasthole, and d = diameter of the reamer hole. (See Figure 3) In the case of several reamer holes, the relation is expressed as: a =1.5D. Where a = C—C distance between the center point of the reamer holes and the blasthole, D = fictitious reamer hole diameter.

Figure 4: The principles of V-cuts and fan cuts.

134

The holes closest to the reamer holes must be charged carefully. Too low a charge concentration in the hole may not



break the rock, while too high a charge concentration may throw the rock against the opposite wall of the large hole with such high a velocity that the broken rock will be recompacted there and not blown out through the reamer. Full advance is then not obtained.

V-cuts and fan cuts

The most common cut with angled holes is the V-cut. A certain tunnel width is required in order to accommodate the drilling equipment. Furthermore, the theoretical advance per round increases with the width, and 45–50% of the tunnel width is achievable. By applying a more advanced arrangement of the blastholes, larger advances can be achieved, but this requires a far better accuracy in the location of the blastholes than normal (see Figure 4). The angle of the cut must not be too acute and should not be less than 60 degrees. More acute angles require higher charge concentration in the holes. The cut is normally in the shape of two Vs, but in deeper rounds may be a triple or quadruple V-cut. Each V in the cut should be fired with the same interval number using millisecond delay detonators to ensure coordination between the blastholes with regard to breakage. The delay between different Vs should be approximately 50 milliseconds to allow time for displacement and swelling. The principle of the fan cut is to make a trench-like opening across the tunnel face. Like the V-cut, it requires a certain tunnel width to accommodate the drilling equipment to attain acceptable advance per round. Fan-cut drilling means only limited constrain on the movement of the blasted rock. The drilling and charging of the holes are similar to that of the cut holes in the V-cut.

Figure 5: Minimized overbreak is crucial for all tunnels that require concrete lining.

Tunnel contour

Accurate blasting is a priority, especially in tunnels where the overbreak has to be replaced with expensive concrete (see

Figure 6: Stoping hole angle should not fall below 90 degrees. The numbers in the firing pattern indicate a firing sequence with 100–500 ms delays.

Figure 5). Numerous blasting techniques have been used to control overbreak and these all have one objective: to minimize the stress induced by the blasting leading to fracturing of the rock beyond the theoretical excavation line. In tunnels, as well as in road and railway cuttings, it is of the utmost importance that the rock around the profile is sound, otherwise fissures and cracks will require costly reinforcement work. It is often claimed that good overbreak control cannot


135

Tunneling Technique

The contour of the tunnel is divided into perimeter holes (wall and roof holes) and lifters (floor holes). The burden and spacing for the lifters can be the same as for the stoping holes. However, the lifters are more heavily charged than the stoping holes to compensate for gravity and for the weight of the rock masses from the rest of the round, which lie over them at the instant of detonation. For the wall and roof holes, it is not uncommon that the same explosives are used as in the rest of the round but with a lesser charge concentration. If the perimeter holes are widely spaced, the contour of the tunnel will then become rough, irregular and cracked, which is far from ideal. For this reason, the “smooth blasting” technique has been developed to obtain a smoother tunnel contour along which the rock is intact. Smooth blasting – where the perimeter holes are drilled close to each other and weaker explosives are used – produces tunnels with a contour that requires substantially less reinforcement than conventional profile blasting.


be expected in all geological formations. That is true, but carefully executed blasting will minimize overbreak, even in severe geological conditions. When smooth blasting, the perimeter holes are ignited after the main blast, and when presplitting, they are ignited before the rest of the round. The charge calculations have to take into consideration not only the perimeter holes but also the holes closest to the contour line. These have to be charged in such a way that they do not create cracks beyond the perimeter of the blast.

Firing pattern

The firing pattern must be designed so that each hole has free breakage. The angle of breakage is smallest in the cut area, where it is around 50 degrees. In the stopeholes, the firing pattern should be designed so that the angle of breakage does not fall below 90 degrees, as shown in Figure 6 on the previous page. It is important in tunnel blasting to have sufficient time delay between the holes. In the cut area, the delay between the holes must be long enough to allow time for breakage and displacement of rock through the narrow empty hole, which takes place at a velocity of 40 to 60 m/s. A cut drilled to a 4 m depth would thus require a delay time of 60 to 100 milliseconds to be clean blasted. Normally, delay times of 75 to 100 milliseconds are used in the cut. In the first two squares of the cut, only one detonator of each delay should be used. In the following two squares, two detonators of each delay may be used. In the stopeholes, the delay time must be long enough – say, 100 to 500 milliseconds – to allow movement of the rock, which generates space for expansion of the adjacent rock to be loosened. For the perimeter holes, the scatter in delay between the holes should be as small as possible to obtain a good, smooth blasting effect. Therefore, the roof should be blasted with the same interval number, normally the second highest of the series. Here we can benefit from electronic detonators because their scatter is practically nil. The walls are also blasted with the same period number but with one delay lower than that of the roof.

Smooth blasting

Smooth blasting is a technique that was developed and refined in Sweden during the 1950s and 60s involving holes that are fired together with the main round using later delays. Small-diameter light explosives with low velocity of detonation (VOD) and relatively low gas content were developed, such as Gurit (see Figure 7).

Figure 7 (top): Conventional charging using ANFO and cartridge explosives. Figure 8 (bottom): String charged bulk emulsion.

136

Today, however, it is more common to use emulsion bulk explosives that are string loaded, applying the same diameters to holes but only partially filling them (see Figure 8). The holes directly adjacent to the perimeter holes must also be given reduced charges to avoid damaging the contour. The



quality of the remaining rock largely depends on the spacing of the holes (S) and the burden (B) as shown in Figure 1, p. 132..For a good result, the ratio S/B should be around 0.8, making the burden greater than the spacing. The increased demand for stable rock surfaces in permanent underground chambers has resulted in smooth blasting being prescribed as the standard method for perimeter control blasting. Fewer cracks in the remaining rock mean less rock reinforcement. The stoping holes in a tunnel blast are closely spaced and constricted, and the crack formation from these holes may extend beyond the final contour if they are overcharged (see Figure 9). The firing of the perimeter holes should be carried out with only a few different sequence numbers for the best results, where the walls holes have the same sequence number followed by the roof holes and then the shoulder holes and lifters. To summarize, smooth blasting offers the following advantages: • Less scaling • Less mucking due to the overbreak • Less concrete when lining

Figure 9: The damage zone from blasted holes should not extend beyond the final contour.

More technology, more precision

Deviation in the excavation of a tunnel from the theoretical line will lead to an increase in construction costs, with a direct impact on four main items: mucking of excessive rock material, sprayed concrete support, secondary concrete lining, and extended construction time. Today, systems such as Advanced Boom Control (ABC) ensure that blastholes are drilled accurately with respect to collaring, orientation, length and straightness. For drill rigs equipped with this technology, the true excavation line can be maintained accurately at roughly 10 cm closer to the theoretical excavation line than traditional techniques. Accuracy is also important when it comes to the location and amount of explosives used, especially when blasting takes place in urban areas with nearby houses, tunnels and structures that are sensitive to vibrations. The concept of smooth and careful blasting implies that small amounts of explosives are used efficiently with a rigorous control of drilling. If drilling or blasting fails in vibration-sensitive areas it can have a significant negative impact on the project. To achieve careful blasting in very sensitive areas, it is advised that a combination of string loaded (pre-chosen charging concentration) bulk emulsion and electronic detonators is employed. This requires a meticulous, predesigned drill pattern yet enables far higher precision, which is the desired end result.

Service platforms on drill rigs are commonly used in tunneling for blasthole charging.


137

Tunneling Technique

This article has been produced with information sourced from Stig Olofsson’s book entitled Applied Explosives Technology for Construction and Mining, published by Applex. ◙

Easy access to information is a prerequisite for tunneling engineers in order to create tunnels that match increasingly complex designs.

A universal tool for the digital age

Increasingly complex designs characterize today’s tunneling industry. The Underground Manager is a holistic support tool that takes planning and evaluation to another level – while also meeting the growing demand for documentation and data gathering. Underground Manager is a family of support software for planning, administration and evaluation of drilling operations in mining and tunneling projects. It is an indispensable tool for fast, efficient and safe handling of data between the site office and the excavation equipment working at the face. Ever since drill rigs became computerized, starting with the Boomer models in the mid-90s, Atlas Copco has provided support tools and software that meet the challenges of evolving practices in the tunneling industry. Underground Manager is unique in that it integrates all of the key aspects of drilling

138

– planning, administration and evaluation – into one and the same system. Over the past decade, urban construction has forged ahead in many parts of the world. This has led to a consistent increase in the number of drill plans that are required for many tunnel projects. In fact, some projects today may involve as many as 300 drill plans, and at times even more. The main reason for this is an increased complexity in tunnel designs in recent years. Acute bends and ramps for road


DATA MANAGEMENT TOOLS

The need for fast, practical and professional data management has never been greater. Today's modern tunneling rigs, such as the Atlas Copco Boomer equipped with RCS, (Rig Control System) feature support systems that enable a seamless transfer of drilling and performance related data between the equipment working at the tunnel face and the worksite office.

tunnels and difficult ground conditions in cities with existing structures near the excavation line, as well as a surge in the number and types of installations, are just a few examples of challenges related to this development. Installations typically involve electrical equipment and cabling, communication and monitoring networks, water supply and ventilation systems. Underground Manager enables tunneling engineers to meet these challenges on a daily basis at the same as it provides support for all types of tunnel projects at worksites all around the world, including tunnels with simple designs. In addition to generating drill plans, it is used as a planning tool that collects, stores and transfers a wide range of drilling data.

Underground Manager – a multifunctional tool

Atlas Copco’s Underground Manager software is a dynamic, Windows™ based computer support tool for a range of tunneling rigs and applications. It is principally used for generating drill plans and provides easy data transfer between the site office and equipment working at the tunnel face. At its most basic level, the Underground Manager’s function is to:

The procedure starts with a 3D image of the tunnel that is imported into the Underground Manager tool. This includes tunnel lines, contours, fix points and laser points. The software is then used to generate drill plans after which data is sent to the drilling rig, which navigates the face using lasers and fix points. When all the holes have been drilled, data is collected regarding the position and length of the drilled holes. Reports are then created and sent to the site office using the IREDES data language standard in Underground Manager.

3D tunnel view

Using 3D modeling saves considerable time and effort when producing drill plans. The easy-to-use interface for


139

Tunneling Technique

• Create drill plans to guide the Boomer operators when plac ing the holes in the correct positions and directions • Provide the drill rigs/drillers with consistent information to position (navigate) the drill rig correctly in the tunnel • Manage drill log files that show where the holes have been drilled

In addition to these features, the Underground Manager can set up a 3D view of the tunnel/drift and charging and ignition plans, while also offering various reporting functions related to round/drill logs, profiler logs and the data provided by Atlas Copco’s Measure While Drilling (MWD) system, which integrates with Underground Manager. The Underground Manager software package is an option that is available when drill rigs are purchased or leased and is delivered in the ABC Regular (Advanced Boom Control) mode as standard, which enables semi-autonomous drilling. This can be upgraded to ABC Total, which provides fully automated drilling for a complete round, whereby the operator monitors the process.


Figure 1– 4: Using the Underground Manager, tunneling engineers can visualize data such as interpolation of contours, drill plans and charging and firing patterns.

Underground Manager (UM) comes complete with a 3D viewing function that can be turned on or off. Compared with conventional blueprints for tunnel systems, 3D modeling greatly reduces the risk of errors. It also means that a drill plan can be produced in a shorter period, with lower project costs as a result. This is all due to better insight into all the elements of a tunnel design. In addition, 3D renderings are very useful for all types of presentations and in coordinating with engineers involved in a project.

and contractors need to be well-equipped for a wide range of design challenges. Drill plans generated using Underground Manager can be tailor-made to the tunnel face with interpolated contours. For example, if a drill plan is to be created for a section of a tunnel that gradually widens but no contour exists for just that position, Underground Manager has a function to interpolate the contours at the face and bottom round positions (see Figure 1). This enables the user to design a drill plan for that unique situation.

The choice of items displayed in 3D view in UM includes: • Tunnel lines • Contours • Navigation items • Hole information • MWD • Bolts • Scanning

The drill plan designer is a key function of Underground Manager where all lines, shapes and holes (length, lookout, type and diameter) are allocated. Each defined section of a tunnel can also be given an individual contour design for generating drill plans, as shown in Figure 2. Any given number of holes can be allocated that may vary between the defined or interpolated contours.

Drill plan generator

Once the tunnel design data has been imported, showing everything from tunnel lines and contours to fix points and laser lines that can all be viewed in 3D, the next step is to generate the drills plans. Software functions for designing drill plans have developed in tandem with market demands for the type and complexity of tunnels. Today, flexibility is key,

140

Once the drill plan is complete, the Underground Manager can be linked up with Atlas Copco’s Rig Remote Access system (RRA).

RRA and Team Server

A prerequisite for obtaining an efficient flow of data logs and drilling reports is the Rig Remote Access (RRA) system, an optional but useful feature for Atlas Copco drill rigs. It allows



for a drill rig to be accessible over a worksite network. All that is needed is a PC with a Remote Display Program or an FTP program. In addition to transferring data whenever the drill rig enters a network area, the RRA system enables the menus on the drill rig display to be remotely accessed. This means that: • The drill rig is always online, and the administrative system can be updated automatically with the latest information • The drill rig operator has continuous access to the latest production planning • Log files are available for the planning department • Service can be planned based on actual needs Team Server is a function within Underground Manager that allows project members to work on the same data from several locations. As an advanced option, Underground Manager can work with a central database, allowing a worksite team to share the same data.

Navigation

Using lasers mounted on the drill rigs that are pointed toward predetermined fix points, a system known as Tunnel Profiler, the driller can navigate the face with maximum accuracy. The fix points are linked from the database in the planning office to the relevant tunnel lines using Underground Manager. There is also an optional method for precise navigation of drill rigs in a tunnel. Total Station Navigation is a function that has been designed to automate the process of positioning the drill rig with accuracy that is better than 1 cm. The system is fast and only takes a maximum of five minutes, compared with 30 minutes or so using manual methods. Moreover, it means that drillers do not have to be present for every positioning task. In the case of dynamic tunnel plans that feature bends, varying inclination, narrow and wide sections, etc., the 3D tunnel view coupled with laser positioning at the face is a crucial support facility for accurate drilling results.

Any changes to the drill plan will also be synchronized and shown in the firing and charging pattern.

Charging and firing pattern

MWD and reporting

By selecting designated sections and using a drawing tool, the Underground Manager enables various blasting scenarios to be tried and tested. Sections of blastholes can be given individual delay times according to a chosen sequence, including block and surface delays, as shown in Figure 4. This is very useful in ensuring that the right ignition sequence is employed.

With today’s systems such as Underground Manager, virtually any activity taking place at the rock face using drill rigs can be logged as data files. Drill/round logs are typical examples of log data used on a daily basis. These show how rounds have been drilled and serve as proof that the work performed meets the requirements for quality (see Figure 5). The data can also be used as build drawings. Subsequently, these drill logs can be summarized in production reports that cover any chosen aspects of a tunnel excavation. Apart from drilling data, the Underground Manager will gather data

Following proper analysis of the geometry and rock conditions, a lot of preparation goes into selecting the right explosives and firing sequences in order to achieve good contours and also to make sure that vibrations do not exceed stipulated limits and regulations for the project. All this can be designed and simulated using the Underground Manager, which offers dynamic drawing tools for both charging and blasting.

A laser pointed at fixed prisms mounted on the rigs and on the tunnel walls, enabling accurate navigation in the tunnel.

Regardless of design complexity, all data from blasted rounds can be analyzed using Underground Manager, which can be useful as a basis for discussion when evaluating a tunnel excavation.

141

Tunneling Technique



on rock bolting and also produce reports that reflect rock reinforcement efforts over any chosen tunnel section. It also gives the possibility to indicate different bolt lengths with different colors. The Measure While Drilling system (MWD) is often employed in projects developed in sensitive host rock either due to nearby structures or installations, such as in urban infrastructure projects, or because of poor ground conditions. In these cases, rock conditions can be visualized through MWD technology and be displayed as maps over the tunnel perimeter. In addition, operators can select specific holes for which MWD is to be switched on with an automatic function for data gatherings. Optional reporting features in MWD also include geological indices based on the drilling process and estimates of hardness and fracturing. This evaluation model incorporates data such as penetration rate, drill speed, feed pressure and other parameters that, when combined, provide an index for rock variations (see Figure 6). This index is often matched with real observations. To create an optimum contour is a key goal in drill and blast tunneling. Any deviations from the specified profile can be costly to correct later on. To this end, the scanning functions provided by the Atlas Copco Tunnel Profiler are highly useful as underbreak and overbreak can be corrected at an early stage of the tunneling cycle. Tunnel Profiler is a fully integrated system for measuring how the excavation conforms to the pre-planned design (see Figure 7). Underground Manager works seamlessly with Tunnel Profiler and will import all data related to the scanned tunnel profile. All data regarding the excavation, from drilling and the placement of holes to bolt holes and profile scans, can be visualized in 3D (see Figure 8).

IREDES – A common language

As more and more equipment used for tunneling becomes computerized and reliant on network communications, there is a growing need in the industry for a common data interpretation “language.” A proposed, universal standard – IREDES – has been developed over several years and is now gaining broad acceptance. IREDES stands for "International Rock Excavation Data Exchange Standard" and is a global not-for-profit initiative founded by more than 20 major players in the mining and construction industry for the development and maintenance of a practice-related standard.

Figure 5–8 from top: Drilling data report; MWD parameters; Tunnel Profiler comparison with theoretical tunnel line; 3D visualization of all excavation data.

142

IREDES brings together equipment suppliers in a common script for data exchange, enabling machines and computers to communicate regardless of the varying software and network systems being used on the market.



The latest version of RCS (Rig Control System) from Atlas Copco enables instantaneous monitoring of tunneling equipment. The system features two multi-functional joysticks for drilling and and a 15-inch touchscreen display.

The question of technology and compatibility between systems is one of the biggest challenges for the tunneling and construction industry going forward. IREDES provides a key solution because it meets the local requirements of any machine user. It covers all data flow required for the manual and automated operation of rock excavation equipment, such as drill rigs, load-haul-dump vehicles, bolting and charging rigs. To a large extent, Underground Manager owes its flexibility to the success of IREDES as this forms the basis for the support tool’s data exchange functions. Using a common electronic language, the benefits of Underground Manager can be enjoyed by the vast majority of tunnelers in all regions of the world.

RCS – a multifunctional platform

The operator console for RCS 5 features two multifunctional joysticks for drilling, a 15-inch touchscreen display and a unique user interface that incorporates elements of today’s consumer technology. The system’s intuitive design, which uses self-explanatory symbols that work globally, has shortened the learning curve for a new generation of tunnelers. RCS is an essential platform for Underground Manager as it makes the tool fully compatible with a broad range of useful functions such as Tunnel Profiler and Measure While Drilling (MWD). Consequently, with this tool, the bar has been raised for accurate drilling and blasting results in tunneling, reflecting the new frontiers of the digital age in civil construction. ◙


143

Tunneling Technique

Rig Control System (RCS) is the standard control system and automation platform for Atlas Copco equipment. Now in its fifth generation, RCS has enabled instantaneous monitoring of operational condition for items such as torque, intercooler temperature, fuel consumption, engine status, penetration rates, data transfer and many more parameters.

All of the functions on drill rigs, bolting rigs, raiseborers, LHDs and a lot of other products can be controlled remotely in semi-automatic or full automatic mode. Furthermore, with recent updates, RCS has made a quantum leap in terms of possibilities for automation and monitoring, including data logging capabilities, serviceability and greater machine accuracy.

The Robbins 34RH C can be used for conventional raiseboring, down-reaming as well as upward boxhole boring.

The raiseboring complement Although mostly used in the mining industry, the raiseboring technique is also being used to great advantage in a wide variety of civil engineering and tunneling applications, here’s why. Raiseboring technology is becoming increasingly useful in different various types of tunneling and civil engineering as an alternative to drill and blast. There are three main reasons for this trend – simplicity, efficiency and, not least, safety.

4. The pilot hole is reamed up to the planned diameter of the raise as the drillstring is reversed back to the machine on the upper level. The cuttings fall to the lower level where they are removed by any convenient method.

This is the basic principle behind the raiseboring technique: 1. The raiseborer is set up on the surface or upper level of two levels to be connected, as shown in Figure 1. 2. Next, a pilot hole is drilled down to the lower level using a small diameter drill bit attached to a series of drillpipe pieces that form the drillstring. 3. On completion of the pilot hole, a reamer head is attached to the drillstring at the lower level.

Typical applications

144

Raiseboring machines have been used in both mining and civil engineering since the early 1960s. It was in 1962 when James Robbins built the world’s first machine and laid the foundation for a new era of underground construction. Boring raises, rather than drilling and blasting them, proved to be faster, cleaner and above all, safer as the operators, using remote control systems, were able to work in well-ventilated


THE RAISEBORING COMPLEMENT

1 Raiseborer set up

2 Drilling pilot hole down

3 Attaching reamer

4 Reaming up

Drillstring

Pilot bit

Reamer

Figure 1: The raiseboring technique.

1 Drilling pilot hole down 2 Attaching reamer 3 Drill string 4 Pilot bit areas away from the hazardous worksite. Atlas Copco Safety is, therefore, a huge advantage, but so is the speed of 5 Reaming up acquired the Robbins brand in 1993 and today more than half of operation. Even in the early days, Robbins machines were 6 Reamer all the raiseboring machines in the world are made by Atlas setting new records by reaming 46 m (150 ft) raises in low Copco Robbins. Furthermore, the ongoing development of strength (soft) granite in just two weeks, a job that previously new models, all equipped with the Atlas Copco Rig Control took months to complete using conventional methods. Before System (RCS), is continuously raising the bar for efficiency, long, raises exceeding 300 m (1 000 ft) became commonplace safety and increased automation. Some of the company’s and raise diameters of more than 6 m (20 ft) are now bored in raise drills are capable of boring holes that are 1 000 m medium to soft rock. It is now possible to bore a single raise long and up to 6 m in diameter, making raiseboring the most 1 000 m in length (3 280 ft) in hard rock. cost-effective way of excavating openings underground. In civil projects raises are now used for wide variety of appliAnother advantage is that because there is no blasting the cations, such as penstocks and surge chambers for hydrorock is not shattered. This leaves a smooth surface inside the power plants, oil and gas pipelines, ventilation for road and rail raise which provides wall stability and a well-defined profile/ tunnels, (see case article from Inje Tunnel, p. 232.) and many cross section. In addition, raiseboring drastically reduces rock more. handling and requires far less manpower.

Horizontal and low angle boring

It is also possible to modify raiseboring machines to bore horizontally and at low angles(see case article "Naples Metro" p. 212.). Standard raiseboring machines, as shown in Figure 3, (next page) are capable of boring raises at angles of up to 45 degrees from the horizontal and have been completed with the addition of only a few accessories and minor adjustments.


145

Tunneling Technique

Raises are developed in two main ways, either by drill and blast or the raiseboring technique. In drill and blast, handheld rock drills and ladders are still used in some countries, despite the obvious dangers. More common is the Alimak method that makes use of a rising driller’s platform. The platform can be used from a single access point but still requires tunneling engineers to be inside the raise during construction, subjecting them to the risk of falling rock.


These modifications generally include a different routing of the gearbox lubrication system, a modified base plate and the addition of a rear support for the guide columns. Horizontal and low angle applications also require different types of mucking as the force of gravity is much less. For example, when horizontal boring, scrapers are used to remove the cuttings from the rock face. This is done to prevent the reamer from being forced upwards by the cuttings, causing unwanted bending stress in the drillstring. A large volume of water is also required to keep the rock face clean. The water can be introduced through the drillstring and either piped from the back of the reamer or through holes drilled in the stem. Additional water can be pumped from the machine onto the face on the outside of the drillstring. Raises larger than 1.8 m in diameter can normally be mucked using a small loader, while short raises can be mucked by hand.

Figure 2: In boxhole boring, the raiseborer can ream upwards with or, as shown here, without a pilot hole.

However, as the weight of the drillstring in a horizontal position causes deviation of the pilot hole, great care must be taken throughout the pilot hole drilling process. If the thrust on the bit is too high on, it will divert the pilot hole upwards. If it’s too low, it will divert the hole downwards. Stabilizers installed along the pilot hole will counteract some of the drillstring weight as will a balanced amount of bailing medium. Other methods have developed such as boxhole boring, pilot down, ream down hole opening, blind shaft boring and downreaming.

Boxhole boring Figure 3: Low angle raiseboring.

Boxhole boring was first employed in the gold mines of South Africa in the early 1970s, following the delivery of modified Robbins raiseborer machines. Boxhole boring is used to excavate raises where there is limited or no access to the upper level and a full diameter raise is bored upward. While boring upward, stabilizers are periodically added to the drillstring (see Figure 2) to reduce oscillation and bending stresses. The cuttings are carried by gravity down the hole and are deflected from the machine and removed at the lower level.

Pilot down, ream down

This method, also known as hole opening in mining, is used to enlarge an existing pilot hole with a small-diameter reamer. The operation is similar to pilot hole drilling, the only difference being that a small reamer is used instead of a pilot bit.

Figure 4: Pilot down, ream down.

146

The small reamer is designed to use the existing pilot hole to guide the drilling, as shown in Figure 4. Stabilizers are used in the drillstring behind the reamer to prevent it from bending. The pilot down-ream down method is only used when a standard reaming system is either impractical or impossible.



Blind shaft boring

Blind shaft boring is used where there is access to the upper level of the proposed raise, but limited or no access to the lower level. With this method, the raise is excavated from the upper level downward using a down-reaming system connected by a drillstring to the machine above it. Weights are added to the reamer mandrel as shown in Figure 5. Stabilizers are located above and below the weight stack to ensure vertical boring. A reverse circulation system, or vacuum system, is typically used to remove the cuttings out of the shaft.

Down-reaming

Down-reaming begins by drilling a conventional pilot hole and then enlarging it to the final raise diameter by reaming from the upper level to the lower level, as shown in Figure 6. Larger diameters can be achieved by conventionally reaming a pilot raise, and then enlarging it by down-reaming. During reaming, the cuttings gravitate down the pilot hole, or reamed hole, and are removed at the lower level. To ensure sufficient down-reaming thrust and torque, the down-reamer is fitted with a non-rotating gripper and thrust system and a torque multiplying gearbox driven by the drillstring. Upper and lower stabilizers ensure proper kerf cutting and reduce drillstring oscillations.

Drillability

Success in raiseboring depends on the drillability of the rock: in other words, the tensile failure of the formation under a compressive load. Studies show that the rock is initially deformed as force is applied to the cutting element, and as the force increases, a pressure bulb occurs. The bulb transmits pressure to the surrounding rock, causing tensile fractures that propagate to the surface and form rock chips. Rock breakage also relies on the interaction of several cutting structure elements and their contact points on the rock. The placement of the cutting structure elements is therefore a critical part of cutter design.

Figure 5: Blind shaft boring.

Cutting structures

Atlas Copco uses three types of cutting structure geometry for raiseboring applications – kerfed carbide insert cutters, rowed cutters and randomly placed carbide insert cutters. Kerf, or disc cutters, use an extension of the rock failure mechanism described above.When properly spaced discs are combined with sufficient cutter force, the result is very efficient drilling since the disc maintains continuous contact with the formation. The interaction between adjacent disc paths produces shear failure of the rock between these paths. The image on the next page demonstrates the pattern of a kerf type cutter on the rock face.

Figure 6: Down reaming.


147

Tunneling Technique

Kerf cutters tend to spall out 10–20 mm (0.4–0.8 in) long banana-shaped chips and smaller, almost circular chips – depending on the formation and the load. Compared to


From top left: Kerf cutter, rowed cutter, random cutter structure. Bottom right: the impact of a kerf cutter reamer on a rock face.

randomly placed carbide insert cutters, kerf cutters tend to require higher thrust and torque to spall out chips but are more efficient if sufficient load and torque are available. The kerf cutter concept is shown in the image series above.

situations where the length of the raise, and the rock characteristics, have proven equal or greater than a machine’s capabilities. The random insert cutter tends to spall out circular chips of approximately 40 mm diameter (1.5 in) or smaller.

Carbide rowed cutters perform somewhere between the kerftype cutter and the random insert-type cutter. The rowed cutter design has multiple rows of inserts (see photos) but no steel kerfs in which the inserts are located. The lack of kerfs allows more room for cuttings removal, less opportunity for abrasive rock to wear away the cutter shell, and greater penetration of the inserts into the rock with less power consumption.

Multiple passes of the cutter can provide a wide range of insert spacing on the rock. Rock failure occurs when sufficient passes have been made to achieve the shear failure between insert pressure bulbs.

The staggered insert location and multiple rows tend to decrease the torque requirements, somewhat similar to the random cutting structure, and the rows of inserts allow for rock kerfs to spall out of the rock, although generally smaller than a pure kerf cutter design. The patented design of random insert cutters employs a random pattern of inserts on the cutter shell to provide a fairly dense axial coverage in a complete revolution of the cutter. This design has shown significant increases in drilling rates while reducing drilling torque, which has proven beneficial for

148

An additional benefit of the random insert location is a reduction in the phenomenon known as “tracking”. Tracking occurs when the insert slips into an existing pressure bulb crater created by the last pass of the cutter. Tracking can wear the edge of the insert prematurely and result in shear failure of the carbide, thereby reducing the penetration rate over time. Tracking can also be reduced in non-random cutters through varying the angles between the inserts in a given row. The random location of the inserts helps produce a new pattern with every pass of the cutter. As a result of this design, efficient drilling can be achieved over a wide range of rock conditions, and is independent of kerf spacing.



Derrick

Derrick Bolts fastening the base plates to the steel structure

Steel structure

Concrete pad

Base plates

Concrete pad Rock bolts

Sloped sunken channel

Rock bolts

Rock bolts

Figure 7: Concrete pad mounting system.

Figure 8: Steel structure – concrete pad mounting.

Site preparation

availability of construction materials are important factors to consider. Once the decision has been made, a detailed design plan relative to the site layout and raiseboring machine needs to be drawn up and approved. The drawing should show the dimensions and position of the mounting system and the exact location of the pilot hole collaring point and base plates.

Preparing the site begins with a comprehensive plan for which the site planner must first receive the following information, well in advance of the scheduled boring date: • Survey drawings showing the proposed collaring point, proposed breakthrough point, and holes axis section. Here, the dip angle and the actual length of the hole should also be specified. • A geological section through the hole axis including its location and a brief geological description. Using this information, the site layout plan can be formulated for the surveyors. The raiseboring site layout must take into account the number and type of drillstring components to be accommodated. Easy loading and removal of these components into the derrick is the main consideration. The raiseboring site must have adequate overhead clearance for the setup and complete extension of the derrick.

Getting set up

The breakthrough site must be excavated to a suitable size to permit removal of the pilot bit and reamer stabilizer, and to install the reamer. The excavation must be large enough to allow the reamer to be positioned and to accommodate the rock cuttings produced by the boring operation. The site must also be accessible for loading and transport equipment. Direct communication between the breakthrough site and the machine operator at the raiseboring site is essential during operations involving the pilot bit/bit reamerstabilizer removal and reamer installation and a telephone system is typically installed for this purpose. This article includes extracts from the Atlas Copco reference book “Raiseboring in Mining & Construction”. ◙


149

Tunneling Technique

Before the raiseboring operation can begin, the derrick must be positioned and mounted at the site. The two most commonly used methods are “concrete pad” or “steel beam” (see Figures 7 and 8). When deciding what type of derrick mounting system to use, the layout of the site and the

Breakthrough site preparation

Rock bolting is an essential step for reinforcing excavated tunnels. Rock bolts are systematically arranged so that load is transferred to stronger parts of the rock. The technique is often supplemented by wire meshing and sprayed concrete.

How to keep rock fall at bay Rock support and reinforcement measures go without saying in today’s world of ever-increasing safety standards. But selecting the right solution for the job at hand is never an easy task. Constructing a tunnel without any form of rock support or reinforcement may well be technically feasible, but it is not an option, especially if the tunnel is to be used for public transportation systems such as roads or railways. The fact is that even with the best reinforcement systems in the world falling rock remains a constant threat.

reinforcement tools, matched to the behavioral characteristics of the rock mass. It is important to integrate rock support thinking at every stage of the work cycle, starting with drilling.

This threat has been reduced considerably in recent years with the development of new, highly effective reinforcement systems, and even more innovations can be expected in the coming years.

Over the past decade, high production, high precision drill rigs have laid the foundation for smooth and controlled blasting. This is crucial because precision drilling helps to minimize the fracturing of the rock mass immediately surrounding the blast area. Similarly, blasting technology has become much more efficient thanks to the development of charging trucks and easier detonation systems.

Selecting the right rock reinforcement system, however, is no easy task. It is not just a matter of selecting the right rock bolts, sprayed concrete (also called shotcrete) and other

Added to this is the recent introduction of many new rock bolt types for different ground conditions, together with a wide variety of concrete spraying and screening systems.

150


ROCK REINFORCEMENT

Making the right choices

Today’s construction planners have more and better equipment at their disposal than ever before with which to tailor a reinforcement system to the prevailing rock conditions. At the same time, this does not mean that all problems have been solved. Tunneling remains a complex undertaking, especially since engineers must constantly adapt to new challenges in order to meet tougher demands in the industry. Besides faster tunneling, these demands include a longer service life for tunnels, increased proximity to pre-existing structures, near-surface construction in urban areas, tunneling below high mountains with high stresses in the host rock, and tunneling under water with great pressure levels. Some basic recommendations for professional rock reinforcement: • Carefully select the rock support system to meet all require ments of the environment, from bad rock and convergence to seismic conditions. • The timing of bolt installations, using rock bolts close to the face, is always important. Bolt installation is usually re quired immediately after excavation, but there are cases when it is wise to allow for some rock deformation (con vergence) before the rock support is installed. Investigate if the system can be divided into primary and secondary rock reinforcement. • In unstable rock mass, evaluate the need for support ahead of the tunnel face. • Choose a rock support system that is adaptable to changing rock mass conditions. • Make sure that rock bolts and sprayed concrete interact well with the rock mass. • Make sure that the support system can handle the expected deformation. As a rule, reinforcement work is carried out immediately after each round has been blasted, and the blasted rock has been mucked out. In some cases, however, several rounds can be blasted without using any rock reinforcement at all or using only concrete spraying. A contrasting method is to apply an initial layer of sprayed concrete before the muck pile is removed. Having said this, a sensitive rock environment may also require short rounds to be blasted, and it may also be necessary to divide the cross section into several segments. The combined effect of this method is reduced vibrations, which means that rock support can be installed with greater efficiency. Splitting of the face may also be necessary in order to be able to handle the stability of the opening.

The MEYCO Versa provides an all-in-one solution for concrete spraying in mid-sized tunnels.


151

Tunneling Technique

The bolting process can also be divided into two stages – temporary (or primary) bolting and secondary (or permanent) bolting. The use of primary bolting will result in fast round times. Permanent bolts can then be installed when it best suits the productivity, although this is not an option in tougher

ROCK REINFORCEMENT

conditions where permanent rock reinforcement is required after every blasted round.

Grouted rebar

Cem Ce

e

ro nt g

nt me

Res

gro

ro in g

in Res

gro

ute u

re ted

ute u

d re

Safety regulations differ from country to country, but the dangers associated with insufficient rock reinforcement are now universally recognized: modern rock support limits rock fall and maintains a safe working environment during construction, not to mention the safety it provides, and reduces cost to society once the tunnel is in use.

bar

b d re

re ted

Safety is paramount

bar

Preventing rock from falling also helps to avoid enormous costs for society that will be incurred if a road or rail tunnel needs to be closed or if water pipelines or other infrastructure utilities get cut off.

ar

bar

In some countries, regulations stipulate that rock support is mandatory and must be performed after each round. In others, the rules are less specific. Nevertheless, it is clear that the regulations regarding rock reinforcement grow more stringent each year and that contractors are getting better at implementing them. A growing trend is for rock support to be designed in such a way that maintenance more or less becomes redundant, although this process is still in its infancy.

Friction bolts

Sw Sw

e

llex

elle

x

kb roc kb roc

olt

Specialized bolting equipment, such as the Atlas Copco bolting rig Boltec, has not been used to any great extent in tunneling. The reason is that it is difficult to achieve high utilization when only one or two tunnel faces are being excavated, which is generally the norm. However, as bolting is a very time-consuming aspect in the tunneling cycle, the latest generation of high productivity bolting rigs are in increasing demand among contractors.

olt

lt t bo e S it Spl t bol t e it S Spl

New thinking

Mechanical Anchored Bolts

Me

cha

n

A ical

nch

d ore

Bol

t

Figure 1: Rock bolts are divided into three categories: Grouted rock bolts, friction rock bolts and mechanical anchored rock bolts.

152

Using bolting equipment instead of manual methods, or even face drilling equipment, is, by far, a safer practice for operators because this equipment has been specially designed to withstand potential hazards that are unique to the bolting process. As a result, mechanized bolting is a preferred method in all situations. One approach is to combine mechanized rock bolting with automation to keep operators out of the most dangerous zones. This is food for thought, especially for equipment manufacturers, and a large measure of new thinking in this area is required to meet the high safety demands of the future. New thinking is also under way regarding sprayed concrete. This involves the training and licensing of sprayed concrete operators to increase the quality of the sprayed concrete applied to rock walls as it is not always easy to estimate the applied thickness. That said, having a quality product to begin with is equally essential.


ROCK REINFORCEMENT

How scaling is performed is dictated by the geological conditions, but there are also many regional differences. However, to provide temporary rockfall protection in the excavation area is always the primary aim of scaling. Any section of rock that may pose an immediate hazard to tunneling engineers and equipment is the key focus. In very weak rock it is common not to carry out any scaling at all. While mechanical equipment is mostly preferred, manual techniques such as crowbars are also often used to remove loose and dangerous rock. And there are others too, such as hydro scaling that involves the use of high pressure water

Radial bolting

Rock bolts used for stabilization are steel rods that are fixed with a mechanical or chemical anchor at one end and a face plate and nut at the other. Their purpose is to transfer load from an unstable rock exterior to the stronger interior of the rock mass. Rock bolts can be divided into three categories. Mechanical anchored rock bolts feature a wedge that is pulled into a conical expansion as the bolt is rotated. Grouted rock bolts are confined in the borehole by means of cement or resin grout, and lastly, friction rock bolts, such as Swellex bolts, consist of a split steel tube along their entire length with a dome-shaped plate at the end (see Figure 1). All three types are used for temporary as well as permanent support under various rock conditions. There are also cases where pretensioned bolts are applied.

Massive rock

The first step to secure the roof and walls at the tunnel heading is scaling, a method which involves the removal of loose rock, fragments or blocks, commonly using a variety of mechanical tools including hydraulic breakers and excavators. This is done after blasting and before mucking and haulage.

Jointed rock

Scaling

Low stress levels

Heavily jointed rock

As with bolting operations, mechanization and automation in sprayed concrete techniques have increased the level of safety for operators. Due to deeper operations and increased regulations, the demand for high quality, durable sprayed concrete, which offers greater safety and reduces health risks and negative impact on the environment, is increasing continuously.

High stress levels

Massive rock subjected to low in situ stress levels. No permanent support. Light support may be required for construction safety.

Massive rock subjected to high in situ stress levels. Pattern rockbolts or dowels with mesh or shotcrete to inhibit fracturing and to keep broken rock in place.

Massive rock, with relatively few discontinuities, subjected to low in situ stress conditions. Spot bolts located to prevent failure of individual blocks and wedge. Bolts must be tensioned.

Massive rock, with relatively few discontinuities, subjected to high in situ stress conditions. Heavy bolts or dowels, inclined to cross rock structure, with mesh or steel fibre reinforced shotcrete on roof and sidewalls.

Heavily jointed rock subjected to low in situ stress conditions. Light pattern bolts with mesh and/or shotcrete will control ravelling of near surface rock pieces.

Heavily jointed rock subjected to high in situ stress conditions. Heavy rockbolt or dowel pattern with steel fibre reinforced shotcrete. In extreme cases, steel sets with sliding joints may be required. Invert struts or concrete floor slabs mey be required to control floor heave.

Figure 2: The impact of high and low stress levels on various rock structures and their consequences for rock stability. Source: Support of Underground Excavations in Hard Rock, Hoek E., P.K. Kaiser and W.F. Bawden. 2000, Balkema.

Spot bolting involves the use of a few bolts in spot locations in the tunnel (see Figure 3). Their location and lengths are

Figure 3: The principle of spot bolting.


153

Tunneling Technique

Bolting is not an exact science as a large number of physical and geometrical parameters are dictated by the ground conditions prevailing on site (see Figure 2). However, three common methods can be grouped under the concept of radial bolting, which refers to the spacing of bolts in a radial arch. These methods are spot bolting and two types of systematic bolting – pretensioned and untensioned bolting.

ROCK REINFORCEMENT

(Hoek & Brown, 1980) is also recommended for which 3D computer modeling is available. Stereographic projection provides a mapping function whereby a sphere is projected onto a plane, which is useful in geophysics and provides rock bolting engineers with a visualization of the loose block. In addition to calculating the dimensions of the loose block, it is important to check that sufficient anchoring length for the chosen bolt type has been allocated to avoid rock bolt failure. Altogether, the accumulated data will help to decide on the length and number of bolts and the bolting pattern that will hold the block. A rule of thumb, however, is that bolts should always extend 1–2 meters into solid rock. If systematic bolting is chosen, the rock will most likely be heavily fissured, impacted by groundwater corrosion or other factors, which means that a systematic installation of rock bolts is required. As indicated in the grey area in Figure 4, the formation of a natural arch is the result of stress redistribution in the rock as the opening is created. The rock in the arch is subjected primarily to compressive stresses. In this example, untensioned rock bolts have been anchored in the natural arch to maintain stability. As most tunnels are permanent, the space between the bolt and the rock can be filled with cement or resin grout.

S

Figure 4 and 5: Systematic bolting using untensioned and pretensioned rock bolts.

determined on site by an engineer after making an assessment of the bolting requirements related to limited loose blocks. The size of these blocks can be determined by observing the position and directions of the fracture planes that define the block. An inclinometer compass may be useful to register the dip of these planes, especially for large blocks. When the block dimensions are known, the weight can be obtained by multiplying the volume with the density (normally 2.6–2.8 t/m³). The volume must be estimated from the location, size and orientation of structures that define the outline of the block. In order to determine the shape and weight, as well as the potential sliding direction of blocks or wedges in the roof and walls, the stereographic projection technique

154

Untensioned bolts are generally preferred in moderately jointed rock where the lower boundary of the natural arch is relatively close to the roof of the opening. This type of bolting is adapted to the natural movement of the rock mass. The length of the bolts is estimated by calculating the block volume, weight and density against the span of the opening measured in meters. The number of bolts and spacing between them is determined by the joint density. In less competent rock structures where the lower boundary of the natural arch is further away, tensioned rock bolts are often preferred. As shown in Figure 5, these form an artificial arch near the ceiling of the opening and are used to increase both the shear resistance of the joints and the normal stress across joints. Various formulas can be adopted to determine the length and spacing between the bolts. All bolts, however, should be of the same length. By using pretensioned bolts to create an arch or beam over a tunnel, the rock can be given a compressive stress of approximately 0.5 kg/cm 2, provided that tensioning is performed accurately. Any existing stresses in the rock must be superimposed on this value.

Mechanized rigs

Manual methods for bolting using handheld pneumatic rock drills were widespread until the advent of hydraulic drilling in the 1970s. Although manual bolting methods are still used in small tunnels, mechanized rigs are dominating today. It is common for tunnelers to employ existing drilling equipment


ROCK REINFORCEMENT

Dry spray method (typical set up)

1. (1 5 m -2 m )

1. (1 5 m -2 m )

Wet spray method (typical set up)

Dry mix

Compressed Air

Liquid accelerator

Concrete, thin stream

Concrete, dense stream

Water Dosing pump

Liquid accelerator

Wet mix

Liquid accelerator

Liquid accelerator

Dosing pump

Illustration: Courtesy of BASF

Compressed air

Illustration: Courtesy of BASF

Figure 6 and 7: The principles of concrete spraying using either the dry or wet spraying method.

that is used for blastholes to bolting. Specialized equipment, however, such as the Atlas Copco Boltec and Cabletec rigs, may be used for larger projects. The fully mechanized bolting rigs of today incorporate all of the benefits of modern technology and can handle a wide variety of bolts efficiently and with maximized safety. At the same time, for most tunneling projects, it is difficult to achieve high utilization of these specialized machines. A semi-mechanized method for bolting is often the preferred choice whereby drilling is performed by a hydraulic drill rig, such as the Atlas Copco XE3 C. The installation of bolts is then carried out by the operators working from the platform mounted on the drill rigs, which is usually equipped with a protective roof. The basket is also used for installing steel mesh. Having said this, it has been proven that mechanization and automation of the rock bolting process offers improved quality and safety in tunneling work.

Applying sprayed concrete – an indispensable technology

Sprayed concrete is a form of concrete that is pneumatically projected onto the rock surface at high velocity using concrete pumps and compressed air. The sprayed concrete is sprayed via nozzles mounted on specialized equipment and sticks to the rock by adhesion. This has a stabilizing effect on the rock.

The sprayed concrete mix differs somewhat from that of regular concrete used in the lining of tunnels. The aggregate has a maximum size of 8 mm, and the cement content is considerably higher. In most cases, there are additives that accelerate the hardening process, which means that the applied sprayed concrete sets within minutes. If the adhesion effect between the sprayed concrete and rock surface is insufficient, the rock can be further stabilized by the installation of bolts and wire mesh. More than a century of scientific research and product development lies behind today’s modern sprayed concrete technology. First used in tunnels and mines in 1907 and patented as Gunite, it consisted of a simple blend of sand, aggregates and water. Today, there is a multitude of different compositions and an equally wide variety of equipment designed to suit an ever-increasing number of applications. Modern concrete spraying, also called shotcreting, must live up to stringent requirements for high quality, durability, resistance to water ingress, and low risk to health, as well as low negative impact on the environment. There are two basic types of sprayed concrete currently in use – dry-mix and wet-mix. For many years, the only way of applying sprayed concrete was to use a dry mix. This involves


155

Tunneling Technique

In general, thin layers are applied that are rarely more than 5 cm in thickness per round. A total layer thickness of 15 cm is common. Due to the adhesion capacity of the sprayed concrete layers, the blocks of rock around the tunnel opening become linked to each other, and the compressive load of the rock becomes more evenly distributed.

There are three principal constructive bearing systems that can be distinguished when reinforcing a hard fractured rock mass using sprayed concrete: • The load of a loose block is transferred by adhesion to sur rounding rock. • The load of loose rock mass or loose blocks are transferred via a sprayed concrete arch to the tunnel profile. • The load of a loose rock mass or loose blocks is transmitted via the sprayed concrete to bolts that are anchored in solid rock. This can also include screen/wire mesh and lattice girders.

ROCK REINFORCEMENT

The addition of steel fiber or polypropylene into sprayed concrete (see Figure 8), which acts as a reinforcing agent, dramatically increases the tensile strength of the sprayed concrete and enables tunnelers and miners to reduce the effort of installing wire mesh, thus saving a considerable amount of time and money. The thickness of the sprayed concrete layers varies, depending on the mix type and the project requirements, but it is normally up to 50 mm for wet mix and 30 mm for dry mix in one path. In many cases though, a thicker application is required, which means that multiple layers have to be applied. A great many parameters are taken into account when matching sprayed concrete to different applications. These include sand/aggregate grading, cement type and amount, hydration control of admixtures, type of plasticizers/super plasticizers, workability, accelerator type, temperature, pulsation, and nozzle systems, to name a few.


Figure 8: An example of steel fiber added to the sprayed concrete.

a premix of sand, cement and aggregate, typically 8 mm diameter stones, which is fed into a hopper. Compressed air is then used to drive the mix in a stream through a hose to a nozzle where water is added (see Figure 6). During transport in the hose, the components are mixed. The wet mix method, introduced in the 1970s, involves premixing sand, aggregate, cement, water and an additive in a concrete plant. This mix is then conveyed by piston pumps through the hosing system to the nozzle, which is positioned 1.5 m from the rock surface, where compressed air is used to accelerate the concrete to a speed suitable for application (see Figure 7). Special chemicals known as accelerators are frequently added to speed up the hardening of the sprayed concrete. In underground construction, the wet method is preferred due to the larger quantities being sprayed, using large all-in-one concrete spraying mobiles, and is generally more advantageous and, therefore, a preferred choice. The dry mix system tends to be more widely used in mining as smaller volumes of sprayed concrete are mainly required, using smaller trucks and more compact equipment. However, in both tunneling and mining, sprayed concrete has been used both for initial excavation support, commonly viewed as temporary tunnel lining, and for permanent tunnel lining.

156

The faster the contractor can apply the sprayed concrete, the better it is for the overall economy of the project, and the more likely that the contractor will meet the contracted completion date. Similarly, the more concrete spraying time can be reduced, the faster the advance, thereby reducing the costs for tunneling. Wet mix is now mainly used in tunneling thanks to its high capacity. On large tunnel profiles such as highway tunnels, up to 24 m3/h of wet mix can be sprayed, whereas the dry mix method would only give a maximum of 10 m3/h. In this context, Atlas Copco MEYCO AG equipment is extremely economical. Due to a patented control system on the concrete pumps, it produces less waste material, known as “rebound,” and uses less chemical accelerator thanks to highly accurate dosing systems. Thus, accurate mixing of concrete and chemical accelerator guarantees high final quality concrete. Moreover, robotic units keep operators out of danger zones and ensure optimal spraying parameters, such as distance of spraying nozzle to rock strata and a consistent spraying angle of 90 degrees, which reduce rebound and give full coverage of rock strata. Robotic equipment also lessens the dependency on skilled operators. It is true to say that concrete spraying is an indispensable element of modern rock support in all subsurface construction. However, the technology is far from complete, and efforts to develop innovations in this field are intensifying. In the future, leading sprayed concrete specialists, including Atlas Copco MEYCO, will develop new methods and products to further increase functionality, performance and safety. This will be especially important as tunnels are increasingly driven through weaker rock strata, in increasing length, and with high overburden.


ROCK REINFORCEMENT

Support ahead of the working face

While working underground within a geologically difficult section, it is important to implement actions to maintain the planned theoretical cross sections during excavation (see Figure 9). The most relevant methods are: • Bolting • Spiling and pipe screening • Injection • Jet grouting • Freezing Spiling, also known as pre-bolting, is normally considered a temporary support measure and is, therefore, performed without corrosion protection. A typical spiling arrangement for a tunnel profile will involve 6 m bolts installed with a spacing of 0.3 m. The recommended bolt angle to the tunnel axis is usually 10–15 degrees. A key consideration in this technique is to achieve safe anchoring at the rear end of the bolt before each new blasting round. A typical procedure will be to use steel straps, radial bolts, and fiber reinforced sprayed concrete as back anchorage. The spiling method may be combined with sprayed concrete to create a temporary support solution. In these cases, bolts with corrosion protection must be used. The bolts are installed in grout so that they adapt to the rock mass. Another method for providing support ahead of the tunnel face is pipe screening (pipe roofing), which has traditionally been used when tunneling in loose material. Today, it is applied when excavating a tunnel in rock mass with wider weakness zones. The method involves the installation of a screen of steel pipes in front of the tunnel face, over the entire roof or part of it, in the tunnel profile. The dimensions of the pipes used are 76.2-139.7 mm diameter. The steel thickness in the pipes is 5–7 mm. Injection is also a common method for improving stability before excavation and is relevant for rock mass with poor stability in combination with water ingress. The weakness zones are characterized by densely cracked rock and uncompacted material. Here, grout will be injected via pre-drilled holes into the rock and seep into the fissures where it sets. Injection grouting holes are usually distributed over the entire tunnel face with a typical spacing of 1–1.5 m. The Tube-AManchette method (TAM) is commonly adopted for injection grouting and involves the use of PVC or metal pipes in which rubber sleeves cover holes that are drilled in the pipe at specific intervals. Grout is pumped to a packer that has been inserted into the Manchette tube. Seals on the packer force the grout through the holes in the tube, past the flexible rubber sleeve, and into the grout zone to help stabilize and/or seal it. TAM pipes installed in the ground will allow grouting to be carried out individually and repeatedly.

It is fair to say that rock support, including scaling, bolting, screening, cable bolting and concrete spraying, is still

a bottleneck in the working cycle in tunneling. Clearly, any reduction in the time required to install the necessary support will have a direct impact on the overall cycle time and, consequently, the overall productivity and efficiency of the operation. Geotechnical monitoring techniques indicate that the greatest relaxation or movement of the rock mass occurs immediately following excavation. They confirm that after a certain period, the rock will establish a new equilibrium based on its own inherent self-supporting capacity, and the best quality rock will remain self-supporting for extensive periods of time without the need for extra support. The poorer the quality of the rock, the greater the degree of support required. It becomes increasingly crucial to install reinforcement before excavation using techniques such as spiling, screening or grouting stabilization as quickly as possible after excavation. Quality and time are, therefore, the two main parameters that must be taken into account when determining what type of rock support should be used. Likewise, tunnel planners involved in the design of rock reinforcement systems must satisfy ever-increasing demands to optimize the designs for maximum safety and economy. ◙


157

Tunneling Technique

Time versus quality

Figure 9: An example of rock support installed ahead of the working face, through a weakness zone with poor rock mass.

The robust Scooptram ST7 loader has a high lifting design for quick and easy truck loading.

Well-matched equipment makes a world of difference

Tunneling engineers are constantly under pressure to reduce the time it takes to complete a project. One of the parameters in meeting these demands is well-matched equipment. It has long been believed that the smaller the tunnel, the less time it will take to excavate. Theoretically, it’s a reasonable assumption, but in practice it is a misconception. The fact is, whatever the size of the tunnel, the true excavation time can only be determined by two factors – the excavation sequence and the choice of equipment. A rule of thumb is that the rate of advance is totally dependent on the time required for each critical phase in the excavation process, which explains why contractors strive to minimize

158

these phases as far as possible. For instance, a simple change in the choice of mucking out equipment will have a profound effect on the rate of advance. Since the introduction of railbound equipment – the first step towards mechanization – productivity in loading and haulage operations has improved tremendously. However, rail bound equipment has obvious limitations. Wheel-bound LHD vehicles, on the other hand, offer faster and more effective mucking due to their flexibility and versatility.


LOADING AND HAULAGE

They are particularly suitable for tunnels where excavated rock needs to be hauled long distances before it can be dumped onto trucks, and equally so if niches, or loading bays, in a tunnel are located at great distance from each other. <300 m

Wheel-bound LHDs

The mechanization of underground production and development work has led to the increasing use of LHD equipment, and with good reason. Not only are these robust vehicles highly maneuverable, they are also able to climb steep gradients and move quickly over long distances. LHDs are specifically designed and built to load, haul and dump material. They can maintain high capacity over long hauling distances and provide a profitable solution in all tunnel sizes. The basic aim is to clear the face of blasted material and haul it to waiting trucks (see Figure 1). If trucks are not available, the LHD will dump the material onto a secondary muck pile to keep the excavation area clean.

<300 m

If the tunnel is too narrow for wheel loaders and conventional (pin on) haulage, emptying the bucket rock into trucks, the secondary muck pile can be placed in turning/loading niches (Figure 2), while in larger tunnels the loading on trucks can be done in the tunnel itself (Figure 3). Equipping loaders with buckets that can be tipped sideways (Figure 4) is another method that has become increasingly frequent, as this offers the opportunity to load the trucks right up at the face. So what makes LHDs so superior for modern tunneling? Here is a shortlist of the main advantages: • Suitable weight distribution • Large bucket volumes • Approximately 50% higher payloads compared with front end loaders with the same engine size • Good stability and high tramming speeds at full loads due to a powerful engine and a long wheel base Wheel loaders are used only for loading and therefore have a simpler and more economical design than LHDs. Their highly mobile and versatile features make them ideal for pile preparation after blasting and short distance hauling. LHDs, on the other hand, are specifically designed and built to load, haul and dump material. They can maintain a high capacity over long haulage distances.

Driver environment

Every Scooptram is fitted with an operator’s cabin or canopy that is certified to meet current regulations, including ROPS/

Figure 1-4: LHD vehicles are suitable for narrow tunnels and long distances, using varying methods of loading.


159

Tunneling Technique

Creating a safe and comfortable environment for drivers is now more important than ever. For example, in the Scooptram, Atlas Copco's LHD, the driver is side-seated for bi-directional operation and maximum visibility.

LOADING AND HAULAGE

Figure 5: When haulage vehicles are in continuous transit, loaders can be used for scaling and clearing out of blasted rock fragments.

FOPS, EC and MSHA. The comfortable seat with plenty of legroom has the correct ergonomic positioning and is designed to reduce driver fatigue and greatly improve safety. The cabins are proofed against sound and vibration, and wider windows give the driver good visibility enhanced by well-placed, high intensity lights.

Choosing the bucket

Although it may be sufficient to let the density of the material to govern bucket selection, this is not always the case when truck loading. In this instance, the bucket should be matched to get the most tonnage in the truck with complete buckets. Rock may swell by as much 60% when blasted, and its loose weight, measured in cubic meters, has to be established before recommendations can be made about bucket size. Likewise, the abrasiveness of the material will affect the choice of wear parts for the bucket. The bucket rated capacity will normally be quoted by reference to heaped capacity, but average fill achieved will depend on other factors such as driver expertise, blasting fragmentation, roadway condition, and route alignment. Atlas Copco establishes a rated tramming capacity for each of its Scooptram models, which is the gross recommended payload. The standard bucket size is then calculated based

160

on material weighing 2.0 or 2.2 t/m³. If the material to be moved is heavier than this, a smaller bucket may be fitted. If the material is lighter, a larger bucket may be recommended to take full advantage of the rated tramming capacity.

E-O-D buckets

Eject-O-Dump (E-O-D) buckets are optionally available for Scooptram loaders where the back height, the maximum height from road base to top of the tunnel, at the dump point is low, preventing dumping of the standard bucket. The movable pusher plate on the E-O-D bucket is retracted for loading the bucket and tramming. This hydraulically operated, hinged plate moves forward from the retracted position to discharge the load with the bucket in a horizontal position. A side-dumping bucket for parallel side dumping is used when there is little room to maneuver and dump with a normal bucket. Less maneuvering means faster cycle times, reduces fuel cost and increases project efficiency so side dumping is ideal for tight places in narrow tunnels

Breakout force

The breakout force in the muck pile is a combination of mechanical and hydraulic force provided by the movement of the bucket and boom by the operator. To reduce


LOADING AND HAULAGE

Figure 6 and 7: Continuous loading requires either wheel-or rail-mounted systems.

bucket-loading time, powerful hydraulics are required with both tilt and lift functions operating simultaneously. The difference between these two types of breakout forces is important in assessing the design productivity of the vehicle, as not all of the hydraulic breakout force can be utilized if it causes the rear wheels to leave the ground. Most manufacturers of LHD loaders use the bucket tilt circuit to maximize the hydraulic breakout force. Breakout force = Maximum sustained upward vertical force, in newton, generated at a point 100 mm (4 inches) behind the leading edge of the bucket of a loader, or behind the foremost point of the cutting edge for a loader having a bucket with an irregular (pointed, curved, etc.) cutting-edge shape, by a lift or tilt cylinder, with the bottom of the bucket's cutting edge parallel to, and not more than 20 mm above, the ground reference plane (GRP).

Continuous loading is a method used in tunneling operations. It employs a unique system of digging arms that loads the rock onto a conveyor, which fills the transportation vehicle at a constant flow. This digging arm-conveyor combination produces uninterrupted optimal volume loading of the transportation vehicle without spillage and offers load capacities as high as 5 loose m³ per minute. During shuttle movements of the transportation vehicles, the loader can be kept busy by cleaning, scaling or gathering sections of the rock mass, as shown in Figure 5. The benefit of the continuous loader is that the muck is loaded directly at the face and renders forward and reverse travel unnecessary. This reduces the need for turning niches and has proven to be highly productive and economical and a more sustainable choice compared to other loading methods in small to medium-sized tunnels. In most small tunnels, a front-end loader has to load the truck from the side, but an Atlas Copco Häggloader moves the rock over itself, front to back. When operating a front-end loader, special niches for loading from the side have to be excavated. With the continuous loader system, these niches are needed only as turning niches for the trucks or as alcoves for bidirectional tunnel trucks and parking. The continuous loader needs either a rail- or wheel-mounted hauling system (see Figures 6 and 7). When a continuous


161

Tunneling Technique

This can result in confusion, so comparisons should only be made between vehicles with similar buckets and where the depth of the cutting edge or bucket volume is the same. In a powerful loader which makes the best use of its hydraulics, the breakout force using the lift circuit should be sufficient to raise the rear of the machine off the ground. The hydraulic breakout force using the lift circuit with the rear of the machine anchored, should exceed the force obtained using the bucket tilt circuit.

Continuous loading

LOADING AND HAULAGE

The Atlas Copco Häggloader enables blasted material to be loaded from front to back, reducing the need for excavated niches.

loading system is combined with transport equipment of the Atlas Copco HäggCon type, for example, the need to excavate niches or alcoves via removal of secondary rock is eliminated, ultimately saving time and cost (see further down, “Shuttle train haulage”). The Atlas Copco continuous loading system, called Häggloader, has a compact design with individual four-wheel steering, which makes sideways moving in larger tunnels easy. Consequently, the loaders can move diagonally and are optimized for narrow drifts and tight cornering. Two different boom applications are available on Häggloader models – dual digging arms or backhoe. The dual digging arms can be maneuvered up and down, outwards and inwards and laterally, within an operating radius of 180 degrees. When using the backhoe system, the machine can also be equipped with a quick coupling device in order to fit a hydraulic hammer or other equipment. The loading capacity of the backhoe system is 70-80% of the standard digging system. For mucking in soft rock areas and scaling of roof and walls, the backhoe system is also recommended.

powered to cope with the steep gradients, have low heights and short turning circles to negotiate underground roadways, and are extremely robust. All Atlas Copco Minetruck versions feature ROPS/FOPS canopies and cabins with back protection and SAHR brake systems for reliable braking. The productivity of trucks is measured by the tonnage carried per km/hour. The cost per tonne of moving the material is then derived from this figure. Atlas Copco Minetrucks have payload capacities of 20–60 t. LHDs and haulage trucks match each other in size. The general rule for filling the Minetruck using a Scooptram is that the loader should complete the operation in three or four clean passes. The Scooptram bucket volume may be changed to achieve this ratio in order to maximize the truckload.

Atlas Copco’s continuous loading system is electrically driven which contributes to low diesel consumption, ventilation investments and running cost. The conveyor on the Häggloader can be raised and lowered to suit the loading height of different haulage vehicles. The Häggloader 10HR, for example, is a wheel-mounted system that operates on ramps as steep as 1:7 going down, and 1:5 going up.

For back-end loading, the bucket width should be 150 mm narrower than the inside dimension of the truck box, and for side loading, the tip of the bucket should extend no more than 300–500 mm below the box side in the dump position. The bucket lip should reach to the centerline of the box for perfect loading. Eject-O-Dump buckets are used when ground conditions do not permit adequate back height for side loading of the truck. Using this system, the bucket pin height should be able to clear the box side. Eject-O-Dump buckets reduce the Scooptram capacity by 10–15%, and this should be taken into account when selecting the most suitable Minetruck.

Haulage trucks

Shuttle train haulage

Minetruck vehicles are specifically designed for underground use for long or short hauls. They have compact dimensions, four-wheel drive traction and articulated steering. They are

162

The shuttletrain is designed for transport in tunnels (and drifts in mining) and is composed of several car units linked together and towed by a locomotive. A conveyor in the base


LOADING AND HAULAGE

of each car transfers the rock inside the train, from the loader in the front to the last car, to fill the complete train. The discharge end of each car fits the loading end of the car behind. Thus the chain conveyors form a single, train-long unit, as shown in Figure 7. Loading and haulage can always be carried out in one continuous operation, without troublesome car switching. By matching the number of cars in one train to the volume of the blasted rock, the complete round can be removed by one train. This method minimizes the need for time-consuming car switching and tramming throughout the tunnel.

Belt conveyors

It is often said that belt conveyors are the most economical mode of transportation. Conveyor belts have traditionally been used for transporting overburden and other materials but in tunneling they are limited to a maximum rock size of about 300 mm. Nevertheless, conveyor belts are much more widely used these days due to the development of mobile and semimobile crushing equipment, which enables crushing to be performed close to the face. Compared to other methods, conveyor belt transportation provides almost unlimited capacity, low operating costs, often lower total investment costs and a better overall environment. However, this method is most cost-effective when dealing with heavy materials and extensive lifting heights. Another advantage is that conveyor belts can be used over long distances without any loss of efficiency.

Loose weight of material

When dealing with rock mass and determining the most suitable loading capacity for a given method, the tunneling engineer will often relate to the loose rock volume that is to be handled. In removing the rock, a certain fixed volume is taken out and crushed into smaller fragments. In its crushed, loose state the material has a greater volume than its original state and this change in volume, from solid to loose rock, can be expressed as the coefficient “swell factor”. This swell factor varies depending on the size and geometry of the fragments and this should be taken into account when transporting large blasted boulders or, for example, crushed gravel.

Evaluating loading equipment

The evaluation process of the loading equipment usually also includes the capacity and cost performance calculations. These calculations provide valuable information when selecting equipment for optimizing performance and tunnel advance rate. It is highly recommended that contractors establish the best possible combination of loading and hauling equipment for any given tunnel project. An optimal distance between loading and turning niches will have a great impact on the loading cycle. In determining the best excavation method, the haulage distances that need to be covered by an LHD or haulage truck, in order to reach the desired capacity, must be calculated. These are just a few of the prerequisites. Other important considerations when choosing the excavation method include: • The amount of rock to be loaded • The loading cycle time in relation to the whole excavation cycle • Size limitations due to tunnel size and available turning and loading niches It is clear that whatever excavation method is chosen, high demands will be placed on the loading and hauling system, and whatever equipment is ultimately selected to do the job will have a profound effect on the economy of the whole project. ◙


163

Tunneling Technique

Figure 8 illustrates that once blasted from the earth, the material comes to rest with “voids” between the different sized, irregularly shaped fragments and it is this “in-situ” volume that is said to “swell”. Depending on the type of material and the degree of fragmentation, it could “swell” by as much as 60% or more compared to its “in-situ” volume. The total weight of the volume has not changed but its weight per cubic measure has changed.

Figure 8: Rock volume may swell by up to 60% when in blasted form.

The Unigrout range from Atlas Copco is designed to suit grouting applications in any tunneling environment. This Unigrout Smart M4 platform is mounted on a truck, which is particularly common for pre-grouting in Scandinavian tunneling.

The essential art of grouting Grouting is an indispensable aspect of almost all of types of civil construction, not to mention mining, and provides a safe workplace for tunneling personnel, long service life for the tunnel and protection of the surrounding environment. Grouting is widely used and has advanced heavily in the tunneling segment. The reason for this is simple. Whether a tunnel is driven by drill and blast or TBMs (Tunnel Boring Machine), surrounding ground needs to be carefully assessed in terms of stability and ingress of water. Injection grouting can be used to strengthen critical areas, to seal against water inflows and to maintain ground water levels according to stipulated rules. Today, successful and economically sound tunnel construction is as much about grouting technique as it is about excavation technology. In fact, without professional grouting, many tunnels in the world would not be possible to drive in accordance with the safety and environmental regulations that are becoming stricter in most countries.

164

Water ingress in a tunnel can affect safety during and after excavation. There are some who are skeptical of the practice and often refer to it as a hindrance to the rate of advance. The missing link is the risk associated with not taking the right measures, which could lead to possible consequences in terms of safety and overall cost. Experience shows that if grouting is not carried out in a proactive way (i.e. pre-grouting) and wherever necessary, it can lead to very time-consuming and costly corrective actions like post-grouting in presence of high water. In some cases, the cost of pre-grouting is below 10% of the cost of post-grouting to reach comparable and satisfactory results. However, in almost all cases, it is not possible to achieve the same tightness when low influx of water is


GROUTING

demanded. When it comes to sealing, however, there can be no discussion. Sealing the ground is a must in order to reduce the impact of the excavation on the surrounding environment. Any change in the water table may result in subsidence and damage to existing surface structures, loss of capacity of drinking water wells, among other undesirable consequences.

Injection grouting

Injection grouting can be defined as an injection under pressure of fluid material (cement-based in most cases) into fractures and cavities in rock, soil or artificial structures. Briefly, this involves drilling a hole that transverses the rock mass’s fissure system or reaches the target cavities in the ground. The hole is then sealed with a so-called packer that is connected via a hose to a pump. The pump then injects grouting fluid into the hole, which spreads into the fissure system and/or ground. Depending on the composition in the grout mix and the extensiveness of grouting, the purpose is to stabilize, strengthen and seal the ground or a combination of all three. Grouting can be used as an independent method, e.g. for sealing, or complement a system like rock support and bolting. Grouting’s main purposes can be defined as: Stabilization and strengthening By injecting grout mix into fissures, cracks and cavities in the ground, we create a skeleton of grout in weakness zones to avoid sliding and/or to improve the ground with respect to load bearing and stress control. In most cases, even if a man-made structure can be an option, it is less expensive to utilize and strengthen the existing rock compared to replacing it with a new concrete construction. Sealing This refers to grouting being developed in order to achieve near water tightness. As can be expected, this often requires dense grout holes to cover most of the fissures, and a variety of grout mix and pressures are employed to reach satisfaction. Generally, water permeability tests in check-holes are used to verify the result achieved. Filling Grouting is utilized to fill gaps; for example, backfilling/ contact grouting behind concrete lining in water-bearing tunnels or simply filling the gap between a reinforcing element and a drilled hole in bolting/anchoring works. Even in bored tunnels where the excavated shape and diameter are controlled within narrow limits, there will be a slight annular gap between the outside of the lining and the inside of the bore.

Grouting is a well-established technique in tunneling and is used to address a variety of challenges. These include water

ingress control (pre-/post grouting) and rock stabilization (pipe-roofing, bolting). One of the most significant tunneling trends today is the increase in the number of projects in urban areas with nearby structures that are sensitive to vibrations. At the same time, greater focus is being placed on tunnel quality, life cycle costs and the working environment. Any, any change in the water table caused by tunnel excavation may result in subsidence and damage to existing surface


165

Tunneling Technique

Tunneling

Unigrout equipment used for anchoring in a slope.

GROUTING

Figure 1: Examples of application areas for grouting, from left: 1. Pre-grouting 2. Curtain grouting 3. Bolting 4. Piling and micropiling 5. Anchoring and slope stabilization 6. Consolidation grouting 7. Pipe-roofing/forepoling.

structures and loss of capacity of drinking water wells, among other undesirable consequences. In other instances, especially in unstable ground containing running and flowing material under pressure or in karst formations, grouting may be necessary to stabilize, strengthen and seal the strata.

Dam construction

The use of injection grouting has a very long history in dams. It is used to strengthen the dam and spillway foundation (as in consolidation grouting), to seal the gap between the concrete and rock (contact grouting), and to seal the rock underneath and on both sides of the dam to reduce water passage (curtain grouting). The curtain grouting technique is known as the most extensive type of grouting. The aim is to seal the rock or Earth’s strata to dramatically reduce water flow and, in certain cases, to cut off groundwater streams by sealing cracks in the Earth’s strata to prevent uncontrolled seepage under the dam.

Mining

In mining, grouting has been used for many years. Although the use of this technique over the past decades has been

166

mainly limited to bolting and water ingress control, it is expected to see an increasing trend in the coming years due to an increased focus on safety and environmental issues.

Surface geotechnical works

There are many other applications in surface geotechnical works globally where grouting is used to assist engineers. These include tunnel portals, road works (slope stabilization) and work site preparations (anchoring).

Grouting equipment

Atlas Copco has been active within the area of grouting for more than 80 years. The company originally started to develop and manufacture grouting equipment in an attempt to rescue expensive holes. These generally occurred when entering poor, fractured rock, in which the drillstring showed signs of getting stuck or flushing fluids were lost. Later on, grouting tools would accompany Atlas Copco diamond drilling equipment on large international tunneling projects. Today, grouting encompasses so much more than traditional ground injection in tunnels, although it is still generally


GROUTING

defined as an injection under pressure of fluid material into fractures and cavities in rock, soil or artificial structures. Depending on the composition and mix of the injected material, it will react physically and chemically inside the rock to varying degrees, but always stabilize, strengthen, or seal the ground or the structure. Mixer Grouting starts with preparing grout mix, and, therefore, all grouting equipment has a mixer onboard. There are mainly two type of mixers used – paddle and high shear colloidal types. Paddle mixers provide a simple setup but limited mixing quality. They are often considered in the lower range of productivity due to the longer time needed for mixing. On the other hand, high shear colloidal mixers offer superior mixing quality covering a wide range of mix designs, including low-water cement (W/C) ratio, and providing higher mixing speeds. Agitator Grout mix is a suspension type and needs to be kept in good shape during injection to avoid settlement of solid particles (e.g. cement). In addition, the air that has been added to the mix as a result of the mixing procedure needs to be released to improve the grout parameters. On the other hand, in most grouting work, it is necessary to perform continuous injection. Considering the fact we make the grout mix in batches, this brings a demand for an intermediate reservoir of grout. All of the above-mentioned functions are fulfilled by an agitator, which is a crucial part of any modern grouting setup. Pump At the heart of any grouting equipment, the pump provides the required flow and pressure of grout. Two main types of pumps are typically used in the industry: piston pumps and progressive cavity pumps. Both types have their advantages and limitations and should be selected based on the project specifications for the grouting work. In general, piston pumps are more common due to the wider range of flow/pressures that are covered. Some of the pumps have independent control over flow and pressure and are also easier to service. Recorder Another key element in grouting work is monitoring and recording of the grouting data. Grouting plays an important role in the safety of mines and civil structures. Since the result of grouting is hidden underground, it is important to carefully control the operation and record the data to enable analysis and verification plus traceability and quality control.

Injection grouting is a common procedure whereby holes are drilled and grout is pumped into the rock to stabilize, strengthen and/or seal the roof and walls of tunnels and other structures, both below and above ground.


167

Tunneling Technique

Grouts and grouting materials There are many different types of injection material – polyurethane, cement acrylics and various hybrids of all of these. Cement is the most tried and tested material and the most commonly used. It has consistently been refined, and the performance of cement suspensions has to a large extent been improved. In addition, deeper knowledge has now been

GROUTING

Importance of water control

To detect water inflow and seal the rock prior to excavation is crucial in order to create the best possible conditions for tunneling. Controlling the water flow is also important in terms of reducing the impact of tunneling on the external environment. Another key consideration is local regulations regarding the disturbance of groundwater levels. For example, in Scandinavia these rules are fairly strict, and as a result, injection grouting is used to seal the rock prior to excavation, as well as for stabilization purposes. In other parts of the world, lowering groundwater levels may be permitted provided they are restored once the tunnel lining is completed. Most tunnels that are located at deep levels, 50 – 100 m, are drained. While injection grouting is used as a general term for stabilizing and strengthening rock or soil with grout, sealing is a more extensive grouting technique whereby the grout penetrates into more joints and fissures to dramatically reduce water ingress. Pre-grouting in tunnels fall into the “sealing” category as described above.

Pre-grouting and post-grouting in tunneling

The most effective form of injection grouting is carried out prior to the excavation of a rock structure. This is known as pre-grouting. Any unacceptable remaining leakage may be sealed off by post-grouting work, i.e., after blasting. The cost of pre-grouting can be 5–10 % of the cost of postgrouting to reach comparable and satisfactory results. The main reason is that both the grout pressure and the grout flow can be fully utilized in undisturbed rock, whereas postgrouting is always performed against a free surface that is often fractured from blasting and excavation.

Figure 2: Long holes are injected with grout resulting in a number of fans that overlap each other.

acquired about rheology, i.e. the flow characteristics of fluids inside the rock’s fissure system. It is usual to distinguish between cement-based and noncement-based grouts. Cement-based products are the most common grouting material used for rock grouting. Non-cement-based grouts are most frequently used in post-excavation grouting when there is a need for an extra round of grouting or in special cases such as a major water inrush.

168

Pre-grouting means that the rock is treated ahead of excavation. These two operations are repeated until a satisfactory result is achieved. The pre-grouted zone should always go beyond the area that is disturbed by blasting, bolting or excavation. Investigation drilling is done during the actual tunneling and in parallel with the pre-grouting work in order to investigate the characteristics of the rock, such as cracks, fissures and fissure systems, occurrence of water, and soft or weathered rock for the next 50 m or so.

Pre-grouting in Scandinavian tunneling

Grout holes drilled for pre-grouting in tunnels are usually 15–25 m long and should end up 3–4 m beyond the theoretical contour (see Figure 2). In addition, they should only be allowed to deviate a maximum of 3–5% from the intended target. This requires starting with guide rods and then using a rod handling system on the drill rig. The diameter of the grout holes is normally 51–64 mm and the length of the holes will also have great influence on deviation.


GROUTING

The Atlas Copco Unigrout platform provides high quality mixing for grouting operations in tunnels, here at the Holmestrand Underground Railway Station in Norway.

When the ground is of poor quality, it is harder to drill the holes. In these cases, it is essential to place the grout precisely where it is required. Where possible, grout holes should be drilled at right angles to the main fissures in order to intercept as many as possible. This is important when post-grouting in tunnels, as well as in traditional surface grouting. It is common practice to start by grouting the floor holes and then continue progressively upwards toward the crown. Even in a situation where, for example, there is a lot of leakage in the shoulder, it is recommended that grouting should be initiated at floor level. One reason for this is that the floor holes are particularly difficult to reach later, and so it is wise to deal with them before they are affected by other holes. It has been found that floor holes with residual leakage are very awkward to grout post-excavation.

Sealing the future

The first known use of grouting stretches back to the 17th century. However, it is mainly over the past decades that grouting techniques have developed, and the use of grouting has taken a leap forward, becoming an essential part of mining and construction projects. Whether it be to reduce leakage of water through rock in tunnels, to strengthen foundations and support the weight of overlying structures such as dam walls, or to correct faults in existing concrete structures, grouting will, in all likelihood, be relied on to an even greater extent in the future as more complex projects get underway. New areas of application for grouting are also likely to arise in the future as the transportation, power and utility needs of society continue to evolve, placing new demands on construction and rock support expertise. ◙


169

Tunneling Technique

Another reason for starting with the floor is that the cement mix is heavier than water, and so by starting at the bottom, gravity is utilized. Water is “squeezed” forward and upward, and cement is injected in, which is often evident by the use of less cement in the uppermost holes.Prior to injection grouting, the drill holes have to be flushed thoroughly in order

to remove cuttings from drilling and other residue or loose material that may interfere with the grouting procedure.

The diamond wire cutting technique provides a versatile way of excavating rock without creating vibrations, which can be harmful in sensitive areas.

On the cutting edge Drill and blast and the TBM method are not the only techniques available for removing rock. There are several other ways of doing it and without the need for explosives. These so-called blast-free methods are now more relevant than ever. An increasing number of alternative rock removal techniques are coming to the fore as more and more tunnel projects are being located in urban environments and other sensitive locations. These so-called blast-free techniques all share the same aim: to reduce, and in some cases eliminate, the problems associated with rock blasting, such as noise, vibration, shock waves, flyrock, dust and emissions and damage of remaining rock. They can be employed in densely populated areas, close to sensitive structures, or in confined spaces where blasting is simply not possible. Typical applications are sections of tunnel projects such as inner-city subway stations and other

170

underground installations associated with transportation, infrastructure and utilities. The most common types of blast-free techniques in use today are: • Diamond wire cutting • Breaking with hydraulic breakers • Hydraulic fracturing • Expansion chemicals • Water cutting Of these, wire cutting has emerged as the most interesting technique largely because it can be used in practically all


DIAMOND WIRE CUTTING

situations where blasting is not permissible. Moreover, it can be used to create architectural designs in rock and results in smooth surfaces that require less post-excavation attention.

How wire cutting works

The wire cutting technique is based on the use of a steel wire with beads impregnated with industrial diamonds and driven around sections of rock in order to cut slabs or blocks that can be removed as individual pieces. The industrial diamonds that are mounted on the wire are sufficiently strong to cut through hard granite rock and a wide range of other materials. The idea of wire cutting is to wear down the rock and create a cut. With one or several cuts, a part of the rock is exposed and can be removed as a homogenous piece.

Figure 1: Vertical cut.

First, holes are drilled into the rock, either vertically or horizontally. Then the wire is passed through the holes and the ends are joined together to form a continuous loop around the wedge that is to be removed. After mounting onto the cutting machine’s flywheel, the wire is rotated under power around the block at variable speeds (see Figure 1-4). As it cuts through the material, the machine is moved backwards, allowing the wire to be tensioned. If this is not possible, the wire can be pushed against the rock mass by using a system of bars and pulleys. This is known as performing a “blind cut” (see Figure 2). In the blind cut method, the wire is fed down the hole and back with the help of a pulley, up to the surface level and then down in the next hole. From the second hole, the wire goes back to the motor. With this system, the cut is made from the surface level down to the desired depth. The wire is cooled with water, and the same water is also used to f lush away the cuttings and dampen the dust. Due to the wire’s high velocity, normally 27 m/s, there is a risk of a lashback if the wire breaks. The safe operating distance is, therefore, the same as the length of the wire. The whole process is virtually vibration-free and relatively quietrunning.

Figure 2: Blind hole cut.

Figure 3: Horizontal cut.

Born in the quarries

Wire cutting was once almost exclusively confined to the dimension stone industry, but it is now proving to be highly useful for an ever-widening wide range of applications in large-scale urban infrastructure projects.

Figure 4: Vertical cutting at 90 degrees.

The principles of diamond wire cutting in rock conditions using four methods.


171

Tunneling Technique

In Stockholm, Sweden, for example, where two such projects are underway – the Northern Link highway and the City Link rail line for commuter trains (see p. 228) – wire cutting has been successfully used to remove rock in several locations where blasting would have constituted a hazard to nearby rail traffic and buildings. In addition, it has enabled the engineers to work longer hours because the low noise level of wire cutting in operation is less of a disturbance to residents.


Other alternatives

In addition to wire cutting, there are also a number of other methods currently being developed that could become serious alternatives to conventional drilling and blasting in a broader sense. These include controlled foam injection, plasma blasting, water cutting, electric pulse boring and electric pulse disaggregation. Controlled foam injection (CFI) This method involves the injection of high viscosity foam into the drill hole. The foam is injected under high pressure, which effectively splits the rock. The equipment used for injecting the foam can be mounted on a drill rig in order to create a continuous excavation process. Plasma blasting In plasma blasting, special electrolyte cartridges containing aluminum powder and copper oxide are inserted into the drill holes. A powerful electric charge is then added that converts the electrolyte in the cartridges to plasma. The plasma expands, generating extremely high pressure as well as heat, causing the rock to split. The method is fast and relatively noiseless. Water cutting Water cutting is based on spraying water at such high pressure, with or without an abrasive additive, that it can cut into rock. This is a variation on water chiseling, a relatively common technique used for exposing rebar during the renovation of concrete bridges. During tests, the method has proven to work best in soft rock formations, but it has also been used in the production of granite blocks. The advantages of this method are similar to those that can be achieved by wire cutting except that a large volume of water has to be taken care of. Electric Pulse Boring (EPB) and Electric Pulse Disaggregation (EPD) This method is based on electric discharges that have an extremely high tension that, when applied in short bursts, can split rock in a very short time. This is achieved via electrodes in fluid. Despite the high voltage level, the total energy consumption is not especially large. In Norway, where the method is being further developed, it is hoped that it will enable extremely deep holes to be drilled to exploit geothermal energy deep in the bedrock. The method is still not commercialized.

Meeting the urban challenge

From quarries to cities: the use of diamond wire cutting machines, such as the SpeedCut, has migrated from the dimension stone industry to tunneling.

172

Many of the Earth’s densely populated areas are badly in need of new tunnels for a multitude of purposes – transportation, water, sewage, power line installations, storage, and much more. At the same time, many municipalities now insist that underground construction is carried out without any risk of inflicting damage on existing structures or of making life intolerable for residents living close to the worksites.



It is largely for these reasons that the two primary methods of excavation – TBM (Tunnel Boring Machine) and drill and blast ‒ are frequently ruled out. Contractors are challenged to propose alternative solutions that can meet stringent demands for a minimum of impact on the surrounding environment and energy efficiency. In this context, diamond wire cutting undoubtedly has the edge. The technique is both environmentally-friendly, energy efficient and highly versatile because it can be used for cutting concrete, steel and other materials, as well as various types of rock. Wire cutting equipment is also easy to operate and can be used with great precision.

Cutting a shaft

One of the fastest growing application areas for wire cutting technology in tunneling is shaft construction, whereby a square or rectangular shaft can be created by wire cutting all four sides. When cutting shafts, four holes are normally drilled from the upper level down to the tunnel or cavern in a square or rectangular shape. The wire is fed through one of the holes down to the lower level and then back up to the surface through another hole. The two ends are connected and fitted on the flywheel of the machine, which is normally mounted on rails at the upper level. The wire is then driven round and begins to wear through the rock. When one side is cut, the wire is moved and cutting starts on the opposite side. The resulting rock slabs are removed either at the upper or lower level in order to be blasted into manageable pieces, and as the slabs are removed from the rock mass, blasting can be carried out without creating large vibrations that might affect the surrounding environment. Under what will be the shaft, a concrete pillar is cast to bear the weight of the rock mass when it is disengaged. The holes are angled out from each other so that the shaft obtains a cone shape. This is to ensure that the rock volume doesn’t get stuck when all four sides are cut. After all sides have been cut, the rock mass will stand on the concrete pillar. The pillar is then blasted, and the cut rock falls down into the tunnel where it can be blasted into pieces for removal. Another solution is to remove the rock upwards, but this may not involve cone shaped shafts. The sides of the shaft are then scaled and reinforced if necessary.

Capacity and productivity

efficiency by approximately 35–40% compared with pulling the wire. Wire cutting technology is in a constant state of development not only to increase productivity, but also to address a constantly growing number of new requirements. It is reasonable to assume that today’s machines will develop into even more useful tools for tunnelers in the years ahead. By significantly reducing post-blasting operations, they will also become more economically justifiable. ◙


173

Tunneling Technique

From the point of view of speed, today’s machines cut rock at the rate of about 5-20 m3/h, depending on the characteristics and compressive strength of the formation. When using the technique with rods and pulleys, blind cut, the wire is pushed against the rock instead of pulled, and this reduces

The "blind cut" technique involves sawing through a series of tightly positioned holes. The diamond wire is fed through one of the holes and back up to the surface through another, with the help of a pulley device, and then down again through the next hole.

The complexity of a tunnel design and ground conditions are typical factors that determine whether the drill and blast or the TBM method (Tunnel Boring Machine) is to be used.

Drill and Blast or TBM? A guide to making the right choice Choosing between the two most common tunneling methods – TBM or drill and blast – is no easy task and requires careful analysis. Below, a look at the prerequisities for decision-making. There are numerous considerations to take into account when deciding which excavation technique to use for tunnel construction – the TBM method (Tunnel Boring Machine) or drill and blast. Some of the issues involved in the process are purely technical and some are economical, but in each case it is essential to conduct extensive investigations and analyses. The prevailing geological conditions are naturally of utmost importance, but very often these are not fully known or fully

174

documented. It is also the case that faulty information and interpretations will have more serious consequences for the TBM excavated tunnel than for the drill and blast equivalent. The general assumption for a small-size long tunnel in rock of moderate compressive strength is that it should be excavated by the TBM method. Similarly, for shorter tunnels with larger and sometimes varying cross sections, the assumption is that the preferred method should be drill and blast. Where geological conditions may be problematic, drill and blast offers a safer way to meet targets and time schedules. However,


CHOICE OF METHODS

deviations from this rule are not hard to find, and it is clear that the factors influencing the decision of which method to use also vary from one project to another. The absence of a logical and well-established decisionmaking procedure may seem odd but is explained by the fact that tunnel projects, to a large extent, involve non-technical professionals. Project owners are frequently public entities, such as highway or railway administrations, and the time span between major tunnel projects is often very long. This means that for some decision makers, a tunnel project and the procedures required can be beyond their scope of experience. In addition to this, there are also political issues that have to be taken into account.

TBM technology

1

2

Most tunneling engineers are familiar with TBM technology whereby all rock excavation is carried out by mechanical means. The actual cutting tool is a large disc (see Figure 1) that rotates and is pressed against the tunnel face with a force large enough to chip the rock. The disc has an outer cutting ring that is mounted on a rotating unit or hub which is equipped with roller bearings that can take both radial and axial forces. The disc is mounted on a circular cutter head. The cutter head is forced to rotate under load, and as it turns, the discs rolling on the rock surface are chipping out fragments of rock in variable shapes and sizes. The cutter head has a defined number of cutters mounted on it and each cutter has an individual distance to the center of rotation. There is another technique called road header excavation where “picks” are used as the cutting tool, but this is used to a very limited extent in tunneling and will not be discussed here.

The disc cutter

Disc sizes vary but for today’s TBMs they are typically 400– 500 mm in diameter. The radial distance between them, as mounted on the cutter head, is typically 75–100 mm. The maximum load that can be applied is in the range of 250– 350 kN. The variation of the load bearing capacity depends on the size of the cutter; the larger the cutter the higher the load it can take. So why aren’t these made larger to be able to take higher loads? The answer is the larger the disc, the larger the contact surface between steel and rock, and consequently the stresses in the rock will not increase as planned.

1. Chipping 2. Adjacent groove 3. Cracks

Figure 1: Cutter being used on a rock surface showing the roller bearing in the upper part of the hub.

cutter, which in itself means higher hourly output from the TBM. It is normally assumed that the penetration increases by the power of two the applied load. To make the cutter rotate on the face and penetrate the rock, there is a need for force to overcome the rolling resistance. The rolling resistance, also called “the drag factor” for the individual cutters, is in the range of 5–15% of the applied load. The deeper the penetration is, the larger the drag factor will become. A consequence of this, when excavating in rock with disc cutters, is that the penetration only rarely goes beyond 15 mm. As the TBM cutter wheel rotates and all cutters are rolling against the surface of the rock at the tunnel face, the added rolling resistances calls for a defined amount of torque to be transferred to the cutter head to make the rotation happen. It is the rotation of the cutter head that consumes most of the power consumed in TBM excavation. The bearings in the cutters are not only limited by the load they can take, but also by the rotation speed of the cutter. With today’s cutters, the maximum applied rolling speed is in the range of 2.5–3 m/s. Consequently, it is the outermost cutter on the cutter head that sets the rotation speed of the cutter head. A 4 m diameter TBM will then have a rotation speed


175

Tunneling Technique

In the past, going back to the 1960s, the cutters were certainly smaller (250–300 mm), but today’s diameters have been used for the two last decades. In reality, very few cutters as large as 500 mm in diameter have been used. Another drawback with very large cutters is the weight. They become difficult to handle. The drive for high cutter loads is based on the condition that higher loads generate better penetration of the

3

CHOICE OF METHODS

lining takes care of loads that may arise from collapsing or squeezing ground. These TBMs can be either single shield or double shield machines. The single shield version has a single tube and no gripper pads through which the torque and thrust reaction forces are transferred into the rock wall. Here, the reaction forces are transferred to the lining segments by hydraulic jacks. This means that the excavation performed by the cutter head has to come to a halt during segment installation.


A TBM setup involves the use of a trailing unit, to support the machine, that may have a length that is ten times greater than the length of the TBM.

that is twice that of a cutter head with a diameter of 8 m. If the two machines give the same penetration per revolution, the smaller one will generate twice the advance rate when boring as the larger machine.

Open and shielded TBMs

The TBM itself is a steel structure that holds the cutter head and provides power and torque for rotation and for applying loads on the individual cutters. The reaction forces that will arise from the action on the tunnel face are transferred via the TBM to the walls in proximity to the tunnel face. The debris or muck that is the result of the cutting action will fall onto the tunnel invert where it is picked up by buckets mounted along the periphery of the cutter head. The debris is then lifted and dropped onto a belt conveyor for transport out of the tunnel. There are two basic types of TBMs: open and so-called shielded machines. By open is meant a TBM (see Figure 2) that has a structure that holds and powers the cutter head without any specific protection from falling pieces of rock, except for a small shield in the roof area just behind the cutter head. This shield allows rock bolts to be installed to stabilize the tunnel, although often with limited effect. The shielded TBMs (see Figure 3 and 4) are encased in a steel cylinder or tube that protects the machine from falling rock. Shielded TBM tunnels are, in most cases, given a precast segmental concrete lining installed at the rear end. This means that only a small proportion of the tunnel periphery is momentarily visible for inspection and that the segmental

176

It was for this reason that the double shielded TBM was invented. Here, the single tube is split into two units, and the cut is made perpendicular to the longitudinal axis of the TBM, meaning that there is a front shield and a tail shield. The joint between them overlaps, making a telescopic movement possible. The front shield that hosts the cutter head advances while excavating, and the rear shield is standing still. The gripper pads that transfer the reaction forces from the TBM to the rock walls as in the case of open TBMs are, in this case, mounted in the rear shield, and square openings in the shield structure allow free passage for the grippers. By this arrangement, which avoids having hydraulic thrust jacks pushing on the segmental lining during excavation, segment installation can be performed while the cutter head is in operation. Reaction forces arising with the turning of the cutter head are transferred via hydraulic jacks to the rear shield. These jacks simply push the front shield, and during the entire stroke the TBM is encased in a tube thanks to the telescopic design. The double shield is not suitable in tunneling conditions where the shield has to be sealed and pressurized to keep water out. The single shield can master the job of keeping water away. It is an effort to build a sealed machine that also has the capability to muck out, considering the pressure on the outside of the TBM shield. This is a common task for those TBMs operating in soil.

TBMs for soil excavation

The majority of TBMs being manufactured today are meant for excavation in soil. Although soil excavation as such is not covered in this article, soil tunneling technology deserves a brief mention. Soil tunneling existed long before the invention of TBMs but was restricted to specific soil conditions that made open face excavation possible, as in the over-consolidated London clay. In mostly dry conditions, support ahead of the face by use of forepoling was adequate to maintain stable conditions and is another example of successful open-face excavation in soil. In wet conditions in fine grained soils, pressurization of the excavation face by use of compressed air was frequently applied. In the 60s a TBM was used for the first time to excavate a metro line in Paris, using air pressure to stabilize the face. The project was successfully completed, and before long, the Japanese discovered that there were other methods available for underground construction in soil than cut and cover.


CHOICE OF METHODS

The open excavations in Tokyo had long been a disturbance to traffic. Major efforts were made to develope so-called slurry shields that were adapted for ground conditions in the Tokyo basin, which consists of thick layers of river deposits. The slurry shields are also called TBM. They create slurry in front of the cutter-head comprised of water, bentonite and excavated loosened soil material. This pressurized slurry keeps the tunnel face stable and is used as a transport medium for the material excavated by the TBM. The slurry is pumped out of the face zone to a surface installation that separates water and bentonite from the excavated material. The cleaned and upgraded bentonite water mixture is then pumped back into the space at the cutter head. This type of TBM excavation requires the construction of a sealed lining right from the rear end of the TBM. It is also necessary to seal the small gaps between the lining segments and the shield in order to prevent water and mud from seeping through into the interior of the TBM. This sealing work, as well as maintaining the correct pressure, is a complex operation. Slurry technology gave rise to the technology known as earth pressure balance. Depending on the gradation of the soil material in certain conditions, EPB (earth pressure balance) technology can be more advantageous than the slurry method. The EPB method stabilizes the tunnel face by means of a paste that consists of excavated material, water and additives of various types. The paste is discharged from the face area by a screw conveyor that is long enough to handle the difference between the hydrostatic overpressure at the inlet end and the atmospheric pressure at the outlet end. There are also other ways to get rid of the muck such as using piston discharging, which may be needed as a supplement to the screw conveyor in cases where the screw is not capable of handling the pressure difference.

1. Shield 2. Cutter head 3. Disc cutter 4. Gripper 5. Thrust cylinder

4

1 2

5

3

Figure 2: A simplified sketch of an open TBM.

1. Shield 1. Shield 2. Thrust cylinder 2. Cutter head Disc cutter 3. Cutter3. head 4. Gripper 4. Disc cutter 5. Thrust cylinder 5. Segment lining

5

1 2 3 4

Figure 3: A simplified sketch of a single shielded TBM.

TBM “backup” unit

So far, we have focused on activities right up close to the TBM. However, it should be noted that the TBM setup also comprises a trailing unit that may have a length up to 10 times the length of the TBM. The sole purpose of this “backup” unit is to support the machine itself.

Considerations when choosing methods

1. Shield

2. Thrust cylinder 1. Shield 3. Cutter head 4. Disc cutter 2. Thrust cylinder 5. Segment lining 3. Cutter head 4. Disc cutter 5. Segment lining 6. Gripper

1

5

2 3

6

4

Irrespective of what is said about the advantages and disadvantages of one or the other of the two methods, the choice

ATLAS COPCO

Figure 4: A simplified sketch of a double shielded TBM.

1. Shield 2. Thrust cylinder 3. Cutter head 4. Disc cutter UNDERGROUND CONSTRUCTION 5. Segment lining 6. Gripper

– TALKING TECHNICALLY

177

Tunneling Technique

The list of conditions that influence the choice of excavation method is long and varied, but the main issues are: • Rock conditions • Geometry of the tunnel • Crew on the TBM and drill and blast equipment • Excavation time and robustness of the methods • Mobilization and site setup • Attitude of decision-makers and costs

CHOICE OF METHODS

The use of locomotives is common for TBM projects to transport out excavated material and deliver tools and materials to the TBM.

is far from obvious. It must be remembered that each tunnel project is unique and short cuts in decision-making exposes the project to hazard.

Rock conditions

With regard to rock conditions, there are two that are always in focus. These are the strength of the rock material and the rock mass stability. In addition, the water conditions, which can be regarded as part of the ground condition, have to be considered. The strength of the rock has a great impact on the advance rate of a TBM, especially when the unconfined compressive strength is more than 150 MPa. The effect of strength is considerably more pronounced for TBM excavations than for drill and blast excavations. For drill and blast it is only the drilling performance that is affected, which typically only takes some 15% of the total time for excavating a full round. With a TBM it will affect 45% of the total time or even more if the cutter wear is related to the strength of the rock, which is usually the case. This means that a misjudgment of the rock strength has much greater impact on TBM performance than on drill and blast. How is the strength of the rock measured? The most common way to measure rock strength is to establish the unconfined compressive strength (UCS). Testing of the rock strength is conducted on a cylinder of rock that has a length 2.2 times its

178

diameter. It is compressed axially and the load when failure occurs is registered. The load is divided by the cross section of the cylinder, and the result is the rock strength. Such tests are costly however, and therefore it is often the case that the number of tests that have been performed for many tunneling projects is inadequate. This fact increases the uncertainty in determining the performance of a TBM on a tunnel project. Experts on both drill and blast and TBM tunneling consider that information founded on unconfined compressive strength alone is not good enough for establishing the performance. Atlas Copco uses the physical property “brittleness” as another factor to consider. It is given almost the same importance as the unconfined compressive strength when estimating the penetration in percussion drilling. The Norwegian (NTNU) DRI method uses a miniature drill apparatus and crush testing of rock samples to estimate the penetration in percussion drilling, as well as TBM penetration rate. These two test methods are related to surface hardness and brittleness, although they are not the result of direct measuring. An indirect and very inexpensive method is the point load test which can be considered a form of indirect tensile strength test. In this test, values are established with which the point load results are multiplied. For example, the compressive strength is generally considered to be 15–20 times greater than the tensile strength, resulting in reasonably reliable assessments of the unconfined compressive strength. The


CHOICE OF METHODS

question, “Why convert tensile strength to compressive strength?” is a relevant one because failure under the percussion bit and the TBM disc cutter is better related to tensile than compressive conditions. The answer is that the UCS factor is widely used, while tensile strength results are very rare. The wear of drill bits and cutters is of great importance, especially the cutter wear that in regular hard rock excavation cases may cost USD 15 per cubic meter just for the cutter, plus the cost of changing cutters which is both labor intensive and time consuming. For drill and blast, the corresponding figure is typically less than USD 2. It is obvious that knowledge of the wear properties of the rock along the tunnel alignment is of the utmost importance. To keep track of the quartz content in combination with rock strength is the key to sucessfully establishing wear costs. There are many instances of how lack of information or negligence has caused major delays and drastic cost increases. There are test methods available to establish the wear of bits and cutters. One of the more well known methods is the Cerchar abrasivity index whereby a needle with a diameter of 6 mm and a conical tip is dragged over the rock sample for a defined length (some 60 mm) and given a defined load (70 N). The indexes are then determined by the diameter of the worn conical tip. In the NTNU testing of wear, rock crushed to powder is passed under a tungsten carbide drill bit or a piece of cutter ring steel at a defined load and wear length. The weight loss of the bit is measured. There are also other wear indexes such as RAI (Rock Abrasivity Index) which is a product of unconfined compressive strength quartz content, adjusted for specific geotechnical conditions. The excavation rate is affected not only by the rock’s mechanical properties but also by rock structures like jointing, foliation and other weaknesses in the rock that occur with some regularity. If discontinuities occur like parallel joints at moderate distances it will certainly boost the penetration of the TBM, and a factor of 2 is not unusual for TBM excavation. The span for the factor is very large and when comparing massive high strength rock with rock of the same type but intensely fractured, the factor will be well beyond 2. When excavating in low strength rock, the factor is closer to 1 than 2. For blast hole drilling this effect is not pronounced. Certainly the percussion rate is increased by closely spaced joints, but that is not a condition that is taken into account because problems like jamming of the drill steel may force the rock drill to hold back from very fast penetration. It can be concluded that TBM is favored by a fractured rock mass but only up to a degree where stable conditions are maintained.

the actual ground conditions. Typical examples of hazardous ground conditions are swelling and squeezing ground where the likelihood of the TBM getting jammed is an obvious risk. Squeezing is a real hazard when dealing with high overburden which could be in the range of 500 meters, while swelling ground can be a real risk for jamming even at low overburden. Highly fractured water-bearing ground is another big threat to TBM tunneling. Major collapses in the TBM area are likely to occur and are difficult to avoid due to the difficulties of treating the ground ahead of the tunnel face. At shallow overburden, shielded TBMs may be capable of handling the situation, especially if the shield can be sealed and operated under outside water pressure. Now how does this differ for drill and blast tunneling? Certainly, troublesome ground with squeezing and swelling will generate problems, but it is far easier to mobilize the means to overcome these issues when drill and blast is used. • The tunnel cross section can be easily expanded to com pensate for the convergences that will arise. • The tunnel face can be stabilized by bolting in the direction of excavation by use of long fiber strands that will be cut as the tunnel-face advances. • Water-bearing and highly fractured ground can be sealed and stabilized by grouting and sometimes spiling or pipe roofing ahead of the tunnel face. No one can say that tunneling in poor ground is an easy task, irrespective of what excavation method is used. It is, however, obvious that the drill and blast method offers more options to overcome the obstacles due to its flexibility and the easy access to the tunnel face that it provides. But when the ground becomes a soil with overburden of less than 100 meters, the open face excavation method can hardly beat TBM technology, unless the tunnel is very short. Here, drill and blast is not used at all unless big boulders occur in


179

Tunneling Technique

Minor instabilities can be handled without any major obstacles by open TBMs and moderate instabilities by shielded TBMs. But when dealing with major instabilities, TBM excavation can run into serious difficulty. It all depends on

A typical narrow tunnel with rail tracks for transportation to and from the TBM, as well as a separate walkway for personnel.

CHOICE OF METHODS

Construction of the Leipzig City Tunnel in Germany involved the use of TBM. Once the tunnel was completed, the walls were knocked down to provide access to the train station at Wilhelm-Leuschner-Platz.

the tunnel alignment that require blasting. It is important to state that there are TBMs designed to cope with soil. Water, even at moderate pressure, in combination with highly fractured rock is almost always troublesome. A way to master those problems is to seal the ground ahead of the excavated tunnel face. This sealing is mostly done by use of the socalled pre-grouting technique. Long holes (20 to 30 m) are drilled from the face contour in the direction of the tunnel. The holes are given a lookout angle and are, therefore, located outside the tunnel periphery for most of their length. The holes are then used for grouting of the rock mass surrounding the tunnel, preferably with cement. This pre-grouting procedure is quite time-consuming and by far much easier to perform when tunneling using drill and blast. There are TBMs that can be closed and withstand outer water pressure, but these are normally designed to cope with pressure less than 6 bar. This type of TBM requires a more advanced mucking system and is primarily used in soil, but can also operate in rock. A TBM designed to cope with water pressure exceeding 10 bar will be very costly and, as a result, very few of these have been built. Temperature is another condition that requires some attention. It is well known that the rock temperature increases when going deeper into the earth’s crust. High temperature

180

is a problem for both men and machines. The TBM itself generates a lot of heat and a rough figure is that some 20 kW hours are consumed for every excavated cubic meter. This power is turned into heat which adds to the rock temperature. It is the same situation for drill and blast operations, but the power consumption is much less and to a large extent released during blasting of the round. This heat is largely exhausted when the ventilation is operating to clear the blast fumes and much of this is also shipped out with the heated muck. Irrespective of the choice of excavation method, pre-investigation and interpretation of the rock conditions along the tunnel route are most important. However, the consequences of faulty results are normally far more drastic for the TBM excavated tunnel than for the drill and blasted one.

The effect of tunnel geometries

The term “tunnel geometry” refers to quite a number of figures that describe the tunnel in terms of length, size, shape, slope, curving, overburden, variation in shape and size and lengths of various rock conditions. Looking at statistics, it is obvious that TBM technology has played a major role, particularly when excavating small and long tunnels. Such tunnels are often associated with waterways in hydropower projects like headrace tunnels and sometimes tailrace tunnels.


CHOICE OF METHODS

In the TBM method, tunnel drives are initiated from "launch box" areas which is a common term for the large caverns where TBMs are assembled onsite.

Typical for these tunnels is that they often have a length of several kilometers, – 5, 10 or even more – and it is common that these tunnels have no variations in cross sections. TBM tunnel walls are generally smooth when compared with drill and blast excavated tunnels and for unlined tunnels this gives an easier flow for water and/or air. This has a large impact on the head losses which is why the TBM tunnel can use a remarkably smaller cross section; a reduction of 25% is not unusual for a small tunnel. For concrete lined tunnels this difference is eliminated, but drill and blast produces more overbreak than TBMs which means larger quantities of concrete are needed for lining tunnels excavated by drill and blast.

Length [m] Diameter [m] x (Unconfined compressive strength [Pa])1/3 Many conditions have been omitted so this estimate can only be considered a simple guide. Why is size (cross section) of the tunnel of major interest? For drill and blast tunneling, larger cross sections do not have to mean that the construction time will be longer. If the increase of tunnel size means that there is room for larger equipment, such as loaders and trucks or drill rigs with more rock drills, or if there is room for placing two drill rigs in parallel at the tunnel face, a larger tunnel may mean an even higher advance rate. If, however, the same gear can be used as in the smaller tunnel, the advance rate will certainly go up. The effect on time, though, is not linear. An increase of the cross section normally means that the drill meters per cubic meter of excavated rock will decrease; the mucking will have higher capacity due to more space; and mobilization times for the various activities in the sequential cycle will not be affected.


181

Tunneling Technique

For large cross-section tunnels, the cost per excavated cubic meter goes down (unless the support measures become a heavy burden due to the size of the opening). The cost reduction as a function of the tunnel cross section is much higher for the drill and blast technique than for TBM excavation, which means that somewhere between small and large tunnels, the drill and blast technique becomes the cheaper alternative. Where on the scale this will occur depends on many other factors, such as rock conditions, access to the site, how easily access tunnels can be made, availability of suitable staffing, etc. A very simplified way of determining which method to choose is to run the equation below. The numerator is the length of the tunnel and the denominator is the product of the excavated diameter

and the third root of the unconfined compressive strength. The length and diameter are given in meters and the strength in Pascal. When the result is larger than 1.5, it is worthwhile to look deeper into the TBM alternative. Please note that there is no deeper science behind this tool.

CHOICE OF METHODS

At the 2.6 km long twin-bore Sparvo tunnel project in Italy, Atlas Copco compressors were used to move the TBM machine into position.

For TBM excavations, the situation is somewhat different. The cutting tool, the disc cutter that rolls on the tunnel face and breaks the rock, has limitations on the load that can be applied and the velocity at which it may roll. It is the material capabilities that set the limits on the cutter bearings but also to some extent the capacity of the cutter ring that interacts with the rock surface. As mentioned before, using 432 or 483 mm (17 or 19 inch) cutter diameters, the rolling velocity should stay below 2.5 to 3.0 m/s. For the small tunnel, three drill and blast headings would probably be needed to match the tunnel meters produced per month and two for the larger one. It is assumed that some of the headings are excavated as double headings. Certainly a higher penetration per revolution would give higher monthly advance rates for the TBMs, but the increase is far from linear as the effective hours would go down. There is a defined amount of work that has to be done per linear meter of tunnel. A higher penetration rate for percussion drilling has no drastic influence on the long-term advance rates. To summarize, in larger tunnels, conventional excavation (drill and blast) is more competitive than in smaller tunnels and that is reflected in the equation on the previous page. Variations of shape and size in the tunnel are difficult to match with TBM excavation. The shape is round and rarely anything else in TBM excavation. (There are a few Japanese machines being built that produce another shape). Sometimes that is an advantage, for example, for water tunnels of different kinds. In sewage tunnels, that are often only partly filled with

182

sewage, the narrow lower part of the round tunnel improves the velocity of the flow, which reduces the risk of clogging. There are possibilities for temporary enlargement of the TBM tunnel section by use of so-called over bore cutters which will allow an increase of the tunnel radius by some 10 to 20 cm. This is something that might be needed in sections of the tunnel where bulky rock support in the form of steel arches has to be installed. This is an option only rarely used. There are tunnel projects where the whole cutter head has been exchanged for a smaller or a larger one. In those cases, there is a need for more modifications of the TBM, but as long as the change of dimension is moderate, it may be a feasible action to take. The lack of flexibility of the TBMs is also valid for curve taking. A typical figure for curve radius is some 300 meters, but this may vary. A limiting factor is the conveyor belt that is transporting muck out of the front area. The conveyor is a long, straight unit on the backup, and in narrow curves it will hit the walls and hamper the advance. There are ways to overcome those problems but they may be demanding. In Japan, a TBM has been designed and built to handle a far smaller curve radius, but special efforts are required. The flexibility that drill and blast technology offers with respect to curvature and alteration of tunnel dimensions along a tunnel route cannot be met with TBM technology. The slope of the tunnel is another issue. In drill and blast tunneling using regular tunneling gear, slopes only rarely exceed 1:6 which means a gradient of 17% or 9.5 degrees (1/6). Steeper


CHOICE OF METHODS

tunnels of (1:4) 15 degrees have been made, but this excavation requires specific means of transport up and down. When going uphill in steep slopes, mucking with a wheel loader is demanding and the capacity for the loader is notably reduced. For TBMs, the slope also affects the progress, at least on steep downhill slopes. The problem is the conveyor transport as the gradient (or slope angle) of the conveyor on the TBM is already going steeply uphill (often 1:6) when the TBM itself is in a horizontal position. By going downhill on a gradient of 1:6, the total gradient will be in the range of 1:3, or 19 degrees. This is beyond what a regular conveyor can handle and the material will slip on the band. Uphill excavations on steep slopes with TBM are fully possible and have been carried out by specially designed machines with extra clamping on the tunnel or shaft wall to avoid back fall of the machine. On gradients of more than 45 degrees, the excavated material will fall down by gravity. On more gentle slopes, assistance with water flushing is needed. When dealing with steep slopes, both excavation methods require deeper analysis of the excavation and muck and haul approach before a tunnel project of that kind should be given the go-ahead. The overburden of the tunnel may be classified as a geometric condition, although the problems associated with the overburden height are also geological or better expressed as a rock mechanical issue. What is meant by high overburden is hard to define. Most people can agree that 1 000 m is a high overburden and that 100 m is a low overburden, at least when dealing with a non-pressurized tunnel face. High overburden may cause instabilities of the excavated tunnel opening, often in the form of a brittle failure called slabbing, which will typically arises in high strength rock like igneous and highly metamorphic rocks. For 200 MPa unconfined compressive strength rock, slabbing may occur at a depth of 500 m.If the tunnel is running close to a slope, it may occur even at lower heights because stress concentrations are not uncommon close to the surface on steep slopes. A comparison between brittle and ductile material is shown in Figure 5.

Brittle

Ductile

Area under curve = absorbed energy

Strain, ε Figure 5: Strength levels of brittle and ductile material.

Rock support for both methods

It is often claimed that a TBM excavated tunnel will require far less rock support compared to a drill and blast excavation. Certainly the smooth mechanical excavation performed by the TBM causes less damage to rock walls and roof. What that means with respect to support is hard to state in general terms. In many cases, TBM tunnels have been given too little support and, as a result, supplementary rock support has to be installed when the ground has failed. As all temporary rock support work is much more demanding to install in TBM tunnels, many of them are given a concrete lining in the form of precast segments that are installed at the rear end of the TBM, which means some 10 to 15 meters behind the face. The segments are installed under the protection of the TBM shield. This is an expensive support solution unless the design calls for a concrete lining. In any event, the rock support required along the tunnel route has to be established before the tunneling work is allowed to begin, and this is valid for both methods. Overbreak of rock means rock that has been excavated beyond the boundary lines. In drill and blast, overbreak cannot be avoided. In the TBM case, some overbreak may be needed to compensate for deviation in the machine’s boring path and wear on the cutters. For water tunnels this is normally not needed as deviations have little effect on water transfer. The flexibility or robustness of the drill and blast method makes it more capable of dealing with unforeseen conditions, and


183

Tunneling Technique

In ductile rock, typically shale, clayey limestone and many low metamorphic rocks, the openings will, when located under high overburden, converge over time depending on the deformation, often called squeezing. Both these failure phenomena (slabbing and squeezing) are more easily dealt with when excavating the tunnels by drill and blast. In drill and blast, the profile can be over-excavated to deal with a converging periphery that in serious cases may jam the TBM. To make it easier for the shielded TBM to handle this situation it can be given a conical or tapered profile, which means that the shield diameter is somewhat larger at the front than at the rear. This will allow for some free convergence in the tunnel heading. Stopping for a longer period, a couple of weeks or even a few days, may be risky as the entire shield, not just the front-end, may get jammed.

Stress, σ

CHOICE OF METHODS

the estimated completion times for a tunnel project are far more frequently met when drill and blast is applied. TBM tunnel projects can, on the other hand, be completed well ahead of the planned date. Again, this mostly depends on better geological conditions than anticipated. Mobilization is another interesting issue. Mobilization refers to the time that passes from the signing of a contract until the start of the excavation work. This time span for a tunnel site is often in the range of three to four months. Within that time, purchase and delivery to the site of the tunnel gear should be completed. This is valid for most of the drill and blast tunnel excavations. For TBM tunnels, the situation is somewhat different. The design and building of a new TBM often requires a full year, and added to that are shipping and site assembly that will take another two months. In some cases with smaller machines based on standard design, the delivery time can be reduced by two to four months, and when going for a first assembly onsite instead of at the manufacturers plant, the time can possibly be cut by a further two months. To summarize, it can be said that, at best, a TBM operation can start some six months later than a conventional tunnel excavation (drill and blast), but that in some cases the time lag can be closer to one year. This means that the completion date for medium length tunnels will not differ very much between the two excavation techniques. This is, of course, more pronounced for larger tunnels as the advance rate for the TBM is less than for smaller ones. It is hard to give a generic answer as to what tunnel length is needed to motivate TBM excavation with respect to completion time. Each tunnel project is unique and needs a proper analysis of what can be achieved. Many sites are located in rural areas, which often means a lack of good access roads or rail connections. Old roads have to be upgraded or new ones have to be built, a fact that may extend the mobilization time and diminish the gap for mobilization between drill and blast tunneling and TBM. It may also be the other way around: that the drill and blast equipment can be shipped on the existing roads, but TBM gear demands a higher load-bearing capacity or better geometry of the road alignment. The access conditions are of great importance. There are even places, especially in the Himalayan area, that are completely closed for months over the winter season so a delay in delivery of one month in the fall may cost another five months due to road closure.

Staffing and crews

There is an evident difference in the demand for skilled labor when considering the two tunneling methods. It is not possible to grab labor off the street and make a drill and blast operator out of him/her. There is a need for months of training

184

under supervision of an experienced operator. The same goes for staffing to carry out the rock support work. Certainly when going for an open TBM where rock support has to be installed the traditional way, the demands on the skill of the support crew are more or less the same as for conventional excavation. For the TBM excavation and mucking, there is far less demand on experience than for drill and blast excavation. If the crew lacks skills, this can easily be provided through training for the TBM method. This also means that in many cases the salaries for the TBM staff can be kept lower. In general there is not much difference in manhours per cubic meter of excavated rock. There may be large variations such as a factor of ½ to 2 when comparing the two methods, but these are rare. The differences will also vary depending on where in the world the tunneling work is carried out. Local regulations and trade union demands will in many places have great influence on the staffing.

Investment and cash flow

There is a great difference in investment cost for a TBM setup and a drill and blast setup. The difference naturally varies depending on the size of the tunnel. For a 6 m wide tunnel, the investment is often four times larger for a TBM set up. To produce the same amount of tunnel meters per month, at least two setups of drill and blast gear will be needed. For smaller tunnels the number of drill and blast setups must be larger than two and more like four to match the meters produced by the TBM gear. Large investments in equipment have to be made before an excavation can begin, and while this is true for both methods, the TBM alternative requires a far greater investment. A large initial investment will be a burden throughout the tunneling project. The higher the interest rate, the bigger the disadvantage for the alternative with high, upfront costs, which is normally the TBM alternative.

Looking to the future

It is always hard to predict the future. We can conclude, however, that the TBM technique is taking larger market shares, although the technique may in many cases generate higher excavation costs. What is the reason for this? Many clients want to avoid blasting operations in built-up areas for a variety of reasons. There will be a shortage of professional drill and blast tunnelers, which is likely to increase the salaries of these professionals. There is already a lack of trained operators in the mining industry. On the other hand, the tunneling market has expanded, most likely due to the technical development of mechanical excavation in soil. People and decisionmakers have become aware of the potential of underground solutions to a much larger extent in both soil and rock. This also means that the drill and blast market will remain and most likely increase in volume. ◙


185

Tunneling Technique


Deviation collaring (cm)

Deviatio

20

10

-20

-10

0

0

10

20

-10

-20

Deviation collaring (cm)

-20

-10

Deviation hole bottom (cm)

20

20

10

10

0

0

10

20

-20

-10

0

-10

-10

-20

-20

0

10

20

Figure 1: The Atlas Copco Boomer range meets 21st century demands for high precision and productivity. Insert: screen view of deviation from targeted collaring position (above) and targeted position of drilled blasthole bottom (below).

The evolution of

tunneling practices

From concepts such as “continuous excavation” to traditional handheld equipment, tunnels are still constructed using a range of varying techniques. A number of trends, however, are discernible that are likely to shape more consistent, global industry practices in the future. Giving a complete and accurate picture of current technical trends in the tunneling industry is not entirely easy as practices vary considerably from one location to another. Whether or not a certain technique catches on depends entirely on the geographical area of a tunneling project and existing preconditions. In Europe, for example, increased safety standards and stricter environmental regulations have greatly influenced

186

technological development, and the same goes for the U.S., parts of South America and many other regions. In these places, combined with other factors such as evolving labor costs, such trends have led to a widespread alteration of applied techniques. By contrast, in some countries, the majority of blasthole drilling for tunneling projects is still carried out using handheld rock drills and pusher legs. Due to low wages, it is still


-20

-10

TECHNICAL TRENDS IN TUNNELING

The drill and blast method is flexible and often favored in urban construction, due to increasingly complex tunnel designs and pre-existing nearby structures.

profitable and, therefore, deemed the most viable option. In these cases, gantries are built with multiple decks to allow for larger numbers of drillers to work simultaneously on the same face. This technique was applied in Europe more than 50 years ago, but that does not mean it will take as long to adopt what would be considered more modern techniques, involving mechanized machinery and computerized control. For example, in the Asian market, a large number of TBMs (Tunnel Boring Machine) are in operation, of which the majority is manufactured domestically. These examples illustrate the point of various trends in the industry depending on location. What is valid for one region may stand in stark contrast to how tunnels are built in another.

Continuous excavation

When looking at tunneling in the Western countries which offer reasonably good salaries, we see a trend towards so called “continuous excavation”, which is the opposite of sequential excavation that typically involves drill and blast tunneling.

At the same time, more and more tunnels are being driven in densely populated areas in complicated host rock with a myriad of existing underground structures, projects for which drill and blast is often the only viable solution. The demand for higher precision, particularly with respect to tunnel lines and grades, is not only being met but even surpassed by the capabilities of computerized technology in today’s drill rigs. Collaring of holes is mostly done at 5 cm from the intended position, while the bottom of the hole is mainly collared 15 cm from the intended position. This task is sometimes carefully monitored, as illustrated in Figure 1.


187

Trends in tunneling

The reason for this might be a shortage of skilled professionals who are more urgently needed in sequential excavation, or, in other cases, because faster advance of the tunnel-heading

is needed for the project. However, this does not necessarily mean faster completion of a tunnel as there may be possibilities for developing several headings at the same time. In the case of small and long tunnels the cost is usually lower for continuous excavation. For small but long tunnels with variable cross sections, the lack of flexibility in the TBM method will mean that the drill and blast method is chosen instead, which has advantages in terms of dealing with complex tunnel designs. Weighing these factors against each other will determine which method is used. TBM minimizes the use of explosives and generally enables a faster completion time, both contributing factors to the method’s growing popularity.

TECHNICAL TRENDS IN TUNNELING

and the gassing agent are mixed while being pumped into the blasthole. The amount to be charged in each hole is established. The flow of bulk explosive and the retraction speed of the hose are controlled by computer, which means that the holes can be evenly filled to a variable degree, for example, 100% or 25% or any other percentage that will fit the location of the hole in the tunnel face, as illustrated in Figure 2. It is very likely that this technique will spread and be further developed.

Increased transparency

Another technical trend is vastly improved transparency in terms of activities at the tunnel face, as a result of advanced data processing capabilities. Drilling data that includes drill performance and actual hole locations can be transferred to other software packages for evaluation and inclusion in improvement processes.

Figure 2: Blastholes with the same diameters are filled to variable degrees with bulk explosives.

Charging and blasting

In addition to drilling, modern techniques in blasting are increasingly being focused on. For example, the use of electronic detonators is clearly growing because they enable more precision in detonation times and sequences. Although they are more expensive than traditional detonators, they give the opportunity to blast larger tunnel rounds even in vulnerable built-up areas as each and every hole can be given a unique number, consequently reducing vibrations. Both underbreak and overbreak are better controlled, making it possible to improve the quality of the rock walls and roofs after blasting. To reduce the amount of sprayed concrete and regular concrete when used as secondary lining, due to a more accurately excavated contour, easily motivates the use of a technique that is somewhat more expensive to acquire. This in no way hampers the progress of a tunnel face. Similarly, trends in charging techniques have centered around the idea of using one type of explosive for the entire round. This has been made possible by the so-called “string loading” technique. In this case, the blasting agent is a bulk explosive that only becomes an explosive once it has been inserted into the blasthole. The bottom booster with the detonator is inserted into the blasthole by the charging hose. The matrix

188

To simplify the digital communication between operating units and software packages, a common standard has been created – IREDES (International Rock Excavation Equipment Data Exchange Standard). This method of data transfer is the first step in allowing integration between digital tunneling technologies. This has enabled site offices to participate daily in the developments at the face. In addition to this, the function Measure While Drilling (MWD) is being employed more frequently as proactive tunneling becomes the norm. MWD provides information on rock conditions for upcoming rounds and helps tunnelers to prepare for adequate rock support. Moreover, MWD is an essential tool in meeting the sharply increasing demands for documentation around the world. Large tunnel openings in poor ground have until lately been excavated by splitting the face into smaller parts that are excavated individually. This sometimes means that installed rock support is dismantled when an adjacent section is excavated. By installing rock support ahead of the face to a much larger extent, it has opened up the possibility to excavate the full tunnel cross section. Although not widely practiced yet, there is a growing interest for these types of solutions. Examples include spiling, pipe roofing and bolting at the tunnel face in long strands, which will be cut as the tunnel face advances. The strands are applied to keep the face from creeping inwards in squeezing ground. To summarize, it can be said that the evolution of tunneling practices, besides the from day-to-day capacity improvements, has brought about more accurate excavation with respect to lines and grades. We can also see an extended and improved monitoring of the excavation activities as well as an increased transparency. Furthermore, recent years have witnessed an increased focus on what lies ahead of the tunnel face, yielding developments such as improved stability, tightness against water leakage and increased monitoring of ground conditions. ◙



189

Trends in tunneling


Zero tolerance: rock reinforcement, modern tunneling equipment and protective gear for personnel are a prerequisite for meeting increasingly strict safety requirements.

Safety underground:

a total commitment

Ensuring the health and safety of tunneling engineers is a top priority for today’s tunnel contractors. Wherever strict regulations have been imposed, accidents have dropped. But more needs to be done to raise the awareness. Safety is one of the construction industry’s prime concerns, especially when it comes to underground operations such as tunneling. The reason is obvious – accidents and injuries can have disastrous consequences, both for worksite personnel and productivity. There is no denying that there are still plenty of accidents that occur every day at construction worksites around the world, some involving fatalities, but statistics indicate that these are generally less frequent and less severe. This is due in large

190

part to the efforts made in recent years by the world’s leading construction companies, as well as equipment suppliers, who have consistently come up with innovative solutions to a range of hazardous operations. The driving force behind this trend is a common desire to eliminate risks and protect the lives of tunneling engineers, as well as recognition of the fact that safety goes hand in hand with the aim to achieve high and sustainable productivity. Today’s tunnelers are better equipped for the job than ever


SAFETY

Site managers are responsible for making safety a priority at the tunneling worksite. This requires regular checks on routines.

with modern headgear, protective glasses, ear protectors, proper coveralls and a range of personal safety devices. In addition, the equipment that is available to them is chock full of automatic features that help to reduce heavy manual labor and the risk of injury. The most obvious of these include good protective roofs known as FOPS (Falling Object Protective Structure) and ROPS (Roll Over Protection System), innovations such as Atlas Copco’s RHS (Rod Handling System), motion sensors, and the mechanization of rock scaling operations – to mention just a few examples of notable safety developments in the past decade.

Putting safety first

Attitudes toward safety in underground construction vary greatly between countries. Although, traditionally at least, high safety standards have been nurtured in the West, many other countries that are now considered fully developed also have a large safety focus which has lead to many improvements.

By contrast, safety in tunneling is very much in the hands of the tunnel site management. Large international construction companies have their own differing codes on safety. While these are generally of a high standard, a major problem in the industry is that large projects tend to involve a great number of subcontractors, and it is difficult to guarantee that these companies adopt the same strict approach toward safety, especially when it concerns smaller subcontractors. But that’s not all. To a much greater extent, the workforce in underground construction is often recruited from different regions and countries, meaning that multiple languages will often be spoken at worksites. Communication may become a challenge, and the misinterpretation of critical information can have a devastating impact on safety. Fortunately, these issues are being addressed in a number of creative ways. Equipment suppliers, for example, can easily


191

Trends in tunneling

It is generally the case that countries with strong traditions in mining will also have adopted extensive safety measures for constrution. Having said that, there is a fundamental difference between mining and construction in terms of safety. To

begin with, mining personnel are usually engaged for much longer periods of time over the lifetime of a mine. This means that miners are more familiar with the rock conditions on the site. Furthermore, trade unions in the mining industry have a strong position and place high demands on mining companies to introduce stricter safety measures.

TT6_3A-Tunneling_ver2

SAFETY

• Walkways to workstations • Drill and Blast excavation • Primary support • Transport • Final lining • TBM (Tunnel Boring Machine) work • Toxic substances in breathing air • First aid The vast majority of all tunnel installations are of a temporary character, as they will be required only during construction. Even so, these installations have to live up to standards for maintaining a well-illuminated and safe worksite. This, for example, means that only licensed electricians are authorized to carry out the electrical work. Similarly, ventilation needs to be installed in a professional, proactive way in order to ensure a good supply of fresh air in all areas where people and machines are at work. To a large extent, the volumes of fresh air deemed necessary are ruled by the power output of the combustion engines that are utilized. A simplified calculation shows that 3 m3 of fresh air is needed for every kW of installed combustion power. The use of rubber-wheel equipment leads to large flows of fresh air, and this means that access tunnels have to allow for extra height to provide space for the ventilation ducts (see Figure 1). Figure 1: The need for fresh air during haulage is calculated on the output of combustion engines. Extra height is required in access tunnels to provide space for ventilation ducts.

adapt their technology to different languages. As is often the case, the weakest link is the human factor, and to emphasize communication methods that can be universally adopted and understood is a key task for tunneling site managers.

Stricter regulations

In addition to the improved standards imposed by contractors, governmental regulations have become stricter than ever before. Increasingly, clearly defined codes stipulate how underground operations should be managed with respect to health and safety. Cooperation is also growing between organizations all around the world, which indicates that safety standards that often originated in the West, in the traditional sense, have begun to migrate to other countries. Although this can be a long process, positive results have begun to show. It must also be borne in mind that health and safety codes are continuously being upgraded, meaning that what is acceptable today may change in the next decade, or in just a few years. Typical health and safety standards, will cover the following aspects of tunnel construction: • Tunneling equipment • Tunnel installations

192

Illumination is another key aspect of tunnel installations that has a direct impact on safety. While all areas should be welllit, special attention needs to be given to areas that feature rescue chambers, power transformers or first aid kits, as well as critical traffic intersections. When it comes to rescue chambers, for example, site managers need to ensure that these are not placed too far from the tunnel face. It is also an advantage to have good lighting at highly trafficked openings in order to keep safety high as the level of traffic increases. In other words, the concept of “think safety” should be an obvious and integral part of project planning in all aspects.

Modern cabins

The FOPS protective design for cabins enables rigs to withstand impact from falling rock, up to a certain kinetic energy level. Today’s modern cabins are also designed for maximum all-round visibility. Although rock fall in tunnel construction is comparatively rare, incidents do occur from time to time where both staff and equipment are affected. For this reason, a zero tolerance approach must be adopted that also encompasses charging – a task that should be performed either from the tunnel invert or from a service platform, thereby eliminating the traditional and hazardous use of ladders. Charging and blasthole drilling should not be carried out simultaneously, despite it being commonplace in some countries. But if practiced, the distance between the hole


SAFETY

Top left: The automatic Rod Handling System relieves drillers from the hazardous task of changing drill rods. Right: a FOPS protected haulage rig cabin.

being charged and the hole being drilled must be two meters, at the very least. When it comes to haulage and the use of wheel loaders, LHDs or continuous mucking systems, it is important to keep staff away from the heading area where machinery is in operation unless they are in the cabin of a loading unit. Here, adequate illumination must also be provided, which is usually solved by the lights mounted on the mucking units.

Zero tolerance

It goes without saying that all equipment manufacturers should also ensure that their products live up to highest safety expectations and actively support the drive for maximum safety in underground construction, thereby contributing to the campaign for ”zero tolerance”. Fortunately, more and more manufacturers are proving that they take this responsibility seriously.

These are just a few examples of what has to be observed in drill and blast tunneling work. Tunneling by TBMs (Tunnel Boring Machines) requires further safety recommendations. In both methods, it is always a good idea to enlist the help of professional service engineers from manufacturers. Not only will they keep equipment working at optimum levels, they often establish a close relationship with operators and, furthermore, are perfectly placed to use their expertise and point out risk areas in order to ensure that safety levels are kept to the highest standard. This article has been produced with information sourced from “The TBG handbook on safety in underground construction”. (TBG means Tief bau – Berufsgenossenshaft and is the German organization for safety issues in underground excavation). ◙


193

Trends in tunneling

At Atlas Copco, for example, one of the world’s leading suppliers, safety is not just afforded the highest priority, it is the very first consideration and starting point for all product

development. To deal with the language barrier, the company is also taking steps to increase the visualization of messages and instructions with graphics, much like the airline industry’s system of symbols.

Adopting a greener mindset not only makes environmental sense, but is economically beneficial and crucial for future competitiveness.

Green thinking for a sustainable future

There is no denying that human activity has severely impacted Earth’s fragile ecosystem and climate. As a result, social aims are being reconfigured – a greener mindset is gaining momentum. Reducing energy spend is both feasible and necessary, and the benefits are far-ranging. Electricity, water, ventilation and compressed air – these factors are the lifeblood of any underground operation. But they also account for why tunneling, and construction as a whole, is and always has been an energy-intensive industry. Contractors all over the world are now facing the pressing challenge of having to reduce their consumption. More than half of the world’s population today lives in urban areas. Cities are expanding at a rapid pace, and according to

194

UN projections, about 70% of the global population will be living in cities by 2050. At this point, it has also been estimated that 9 billion people will be living on the planet – all requiring access to the necessities of life: clean water, food, shelter, electricity and healthcare. But that’s not all. Smarter housing solutions and infrastructure systems will be crucial in order to sustain the global population of the future, and this includes tunnels for transportation and a wide


ENERGY CONSUMPTION

The electrically powered equipment for rock excavation that is now available, including loaders and trucks, is up to 70% more energy efficient than diesel options.

range of other applications. Not only will tunnels need to be more advanced and durable in their design, but also more energy efficient throughout their operational life – and it all starts with the construction phase. It has been proven that the development of society over the past century has had a negative impact on the Earth’s climate and fragile ecosystem. As global awareness grows about the environmental problem, the ingenuity of engineers is attracting the spotlight. While it is impossible to construct tunnels without energy, there are many solutions available that make for good news.

are very different, but also the preconditions for excavating large volumes of rock. All of these factors have an impact on energy consumption, ranging from ventilation to combustion engines, pump systems and compressed air.

Good housekeeping – a green mind-set

It is becoming increasingly clear that reducing CO2 greenhouse gases, which have a negative impact on the world’s climate, not only makes environmental sense, but is also sensible from an economical perspective. For example, the need for fresh air and ventilation at tunneling sites is one of the largest consumption areas as far as electricity is concerned. Here, recent innovations, such as “ventilation-on-demand” systems that feature frequency inverters, are making a significant difference – reducing energy consumption by as much as 30–50%.

Green thinking is on the rise in the construction industry. Having a comprehensive plan in place for how to conserve energy and minimize or eliminate waste, toxic chemicals, and all forms of contamination is becoming an international requirement for many projects.

“How can resources management be improved?” is a crucial question for today’s site managers. Water retention is another typical example where modern systems can give rise to reduced total consumption. In tunneling, water is primarily


195

Trends in tunneling

Stricter demands are imposed regarding environmental issues, but with the current high electricity costs and those expected in the future, the need to both increase productivity and reduce total energy consumption cannot be ignored. As such, adopting a philosophy of good housekeeping is essential for any project. Tunnels can be short or long with a large or a small cross section. They can be located near the surface or deep down in the ground where not only rock characteristics

Whether a tunnel is excavated by conventional drill and blast or TBM (Tunnel Boring Machine) also makes a difference. In terms of power consumption, ballpark figures do exist, and for conventional excavation, they indicate some 10 kWh per excavated m3. The corresponding figure for TBM excavations is 20 kWh/m3, but this figure can vary greatly.

ENERGY CONSUMPTION

Operator activates air-mist flushing (adjusts amount of water to control dust), rotation, feed forward and percussion and begins to collar hole.

Operator drills the hole as normal, though may adjust the amount of water introduced into the flushing stream to keep dust production under control.

Figure 1: Water is used in tunneling to keep dust levels low and to flush out the drill holes. The Water Mist solution from Atlas Copco uses compressed air and reduces the need for flushing water by up to 80%.

consumed for the purposes of binding together dust particles, but it is also used to flush away the residual product of drill cuttings from the drill hole. There are already solutions available for reducing unit consumption on drilling machines by mixing incoming flushing water with air. Atlas Copco has an available option called Water Mist (see Figure 1), which can reduce the need for flushing water by up to 80%. Although compressed air via onboard compressor or a compressed air system will then be needed, it is an option worth considering.

Energy rules the worksite

The use of combustion engines in tunneling increases the demand for fresh air ventilation and, hence, the consumption of energy. But if all combustion engines were banned from construction sites, there would still be a considerable need for fresh air. TBM tunnels usually have a very small input from combustion engines, yet the demand for air velocity at the tunnel heading is at least 0.5 m per second, and this often increases as more heat and dust are generated. This means that for long- and small-diameter tunnels the power consumed by the ventilation system may be as high as the power used by the TBM itself to cut the rock and advance the tunnel. Similarly, in drill and blast tunneling, there is a minimum demand for fresh air. Even if all the equipment used for mucking out is electrically powered, other equipment used for drilling, bolting, concrete spraying and scaling is mostly reliant

196

on combustion engines for transport, and it is believed this is not set to change any time soon. As a general rule, the demand for fresh air is roughly 3 m3 per minute and kW of installed combustion power. In order to fully grasp the crucial necessity for energy in all aspects of tunneling, it is useful to give an idea of what power installations might be needed at a worksite when excavating a 70 m 2 large and 4 km long tunnel using the conventional method, drill and blast. Drill rigs typically consume a lot of energy. Each rock drill is supplied by a 75–90 kW electric engine, and for a 70 m 2 tunnel, the rigs are often equipped with three rock drills. The drilled meters for every m3 of excavated rock, including drilling for rock bolts and other purposes, is roughly 3 m/m3 and will result in a power consumption of 3 kWh/m3. Scaling of the roof and walls at the face will engage the scaling unit for about an hour, although the rig’s hydraulic hammer will only be used 50% of the time spent at face. The power consumption will then be 0.3 kWh/m3. If the tunnel is given a sprayed concrete lining with a nominal thickness of 10 cm, the average quantity coming out of the spraying nozzle is about 4 m3/meter of tunnel. This gives a power consumption of 0.5 kWh/m3 for the concrete spraying work. Consumption in the form of diesel fuel, primarily used for loading and muck transport, has to be added to get the full picture of energy demand in tunneling. Rubber-tired equipment has a much higher rolling friction to overcome when compared with rail-bound transport. The difference is


ENERGY CONSUMPTION

more than tenfold, at least, when compared to rubber-tired transport on roads, considering the typical standard of road surfaces in temporary tunnels. If diesel trucks and loaders are employed to carry out a mucking out assignment, using the same 70 m2 tunnel example and assuming that the face is located 4 km away from the portal, the transport power need will be 1000 kW. Using 3 m3 per minute of installed kW, the required air flow will then be 50 m3/sec (1000x3/60). Electric power is also needed for water and sewage pumping. The latter can vary considerably depending on inflow quantities, pumping distance and lifting height. When considering the total power consumption at a worksite, the input of diesel fuel should be included in the breakdown. Calculations here are based on the assumption that one liter of diesel has an energy content of 10 kWh per liter. The fuel consumption corresponds to 0.8 liter of diesel for each excavated m3 of rock in the above tunnel example. This gives 8 kWh per m3 of excavated rock. The explosives used to blast and loosen the rock hold about 1 MJ/kg. A charging density of 2 kg explosive agent/m3 yields a consumption of 0.6 kWh/m3 of loosened rock. In the quest to lower energy consumption in tunneling, the most obvious activities focused on are mucking out and ventilation, partly because they are the largest contributors to high energy consumption and because they both offer good opportunities for achieving significant reductions.

A better way to ventilate

The need for ventilation capacity has increased over time due, on the one hand, to meet increased demands for an improved working environment and, on the other, to the fact that tunnels are increasingly being driven at greater depths, with more complex designs and bigger machines. However, it is often the case that small and long tunnels are, comparatively, the most energy intensive. The reason for this is that small, long tunnels have small cross sections that only allow for limited space when installing fan ducts with a diameter large enough to provide a moderate velocity of the fresh air flow. For example, if a long tunnel requires 25 m3/sec of air at the inlet, the power consumption will triple as the tube diameter goes from 1.4 m to 1 m as the air pressure increases. For long TBM headings and small vent tube diameters, the power consumption may be almost as great as the rock cutting work.

Ventilation systems must be installed by professional technicians to minimize the risk of air leakage and wastage of energy.


197

Trends in tunneling

This often presents site managers and planners with a tricky equation. The rule of thumb is that the longer the tunnel, the greater demand will be for fan capacity in order to maintain the required flow of fresh air at the face. Longer tunnels need higher air frequency and more air as more trucks and/or LHD vehicles will be needed to transport the rock. Another reason the ventilation output is increased in longer tunnels is that

ENERGY CONSUMPTION

Figure 2: Ventilation-on-demand systems can reduce energy consumption by as much as 30–50%. They use frequency inverters to adapt the supply of fresh air to each ongoing activity at the worksite.

longer ducts often involve a greater risk of leakage along the tunnel route, which needs to be compensated. Beyond this, blasting also puts high ventilation demands on projects because toxic fumes need to be vented before tunnelers can safely return to the worksite. Diesel-operated loaders often have a greater demand for ventilation in order to provide a good working environment. Electrically powered loaders with cable operation have been available for a long time but have not enjoyed major success despite many advantages. A big disadvantage is that the cable length often reduces the machines’ working area, in addition to the fact that they cannot move around with sufficient ease and efficiency if there are several tunnel headings and muck points. The industry is expecting solutions whereby electricitypowered underground vehicles can be maneuvered independently without cable installation. Until then and even beyond, it will be imperative to manage ventilation systems in better ways. Some tunneling projects are still losing fortunes in ventilation costs because they allow these systems to operate at full flow at all production points at the same time, even in areas where no excavation is taking place.

198

This method of working is growing obsolete with the arrival of modern, ventilation-on-demand systems. Using sensors and automated communication between equipment and ventilation control, these systems will regulate the air flow frequency in the ventilation fans according to specific areas of a construction site and ongoing activities. As illustrated in Figure 2, frequency control provides ventilation only where it is needed and closes it down in areas that are lying dormant – enabling huge savings, 30% or more, in energy and costs.

Haulage choices: pros and cons

When choosing the right system for mucking out and haulage, a number of advantages and disadvantages will be weighed against each other. Although rail-bound transport drastically reduces the demand for fresh air, it has its limitations in terms of grades and curves in the tunnel. In other words, locomotives are less flexible with complicated ground conditions. Similarly, electrically powered loaders also have the benefit of lowering the demand for fresh air, but here there is also a trade-off when it comes to flexibility.


ENERGY CONSUMPTION

Using conveyor belts instead of haulage vehicles as a haulage system in TBM excavations can significantly reduce the consumption of energy.

In TBM tunneling, conveyor transport has become a favored method for muck transport. This is probably not primarily due to potential energy savings, but rather the increased reliability of such a system and its capability of maintaining a high and constant capacity while allowing space in the tunnel for other transports. Contrary to TBM excavation, drill and blast excavation requires crushing of the muck before it is loaded onto the conveyor, and that entails a certain energy demand, but it is often nominal by comparison. The required fragmentation is usually about 20 cm in diameter, and that means for a tunnel of 70 m 2 an energy consumption of ½ kWh/ton. The power consumption level for TBM straight conveyor setup would be for the 4 km long heading of the 70 m2 tunnel 1.5 kWh/m3, which is significantly lower than for haulage with trucks. Having said this, conveyor solutions for conventionally excavated tunnels require longer tunnels in order to motivate the cost and time savings for these installations.

The way compressed air supplies are arranged is an area that needs close attention. On larger tunnel projects, the air is

In the tunneling industry, it is still possible to come across nightmare examples where half of the compressed air escapes along the way through joints and goes to waste, and even the best system can lose up to 30%. But there is a solution here, too. Installing the compressors close to where the air will be used will reduce leakage and the cost of the electricity needed to drive the air such long distances. By optimizing the entire value chain, from electricity and water to ventilation and installations, tunneling contractors can reap substantial cost savings that will both strengthen their ability to comply with 21st century environmental regulations and secure competitiveness in tomorrow’s construction market. This can only be achieved by bringing monitoring to a higher level that enables data gathering and an overview of all modern equipment and communications systems. ◙


199

Trends in tunneling

Improved installations, more monitoring

often supplied from a fixed installation on the surface and is delivered into the tunnel by running galvanized pipe bolted together every five meters, usually along the walls. This pipe system can be up to several kilometers long, with great risk of leakage from the joints.

B Compact and flexible equipment is often used in various tunneling applications. Here, a FlexiROC T20 R is deployed for bolthole drilling as part of a reinforcement/rehabilitation plan.

Keeping tunnels up to scratch When a newly constructed road or rail tunnel is finally opened to traffic, the cost of construction comes to an end but the cost of maintenance has only just begun. Interestingly, these two items are very much related. How do tunnel builders calculate running costs? The short answer is “experience.” But in many cases, the cost of maintaining a tunnel in good working order is not planned at all beyond carrying out repairs whenever needed. The fact is that the running costs, which include the cost of maintenance, take effect from the very first day the tunnel is completed and start to rise even if the tunnel is not yet in use. The reason is that a tunnel is a living structure. It is affected by changing weather conditions, groundwater flow, and aging of installed rock support, as well as plastic deformations of the ground around the tunnel opening. As a result, all tunnels have to be repaired or renovated a number of times over their lifetime, and it is these costs, together with the cost of construction, that constitute the tunnel’s life cycle cost.

200

To get even deeper into the cost structure, the life cycle cost also includes the costs for interest on all investments for maintenance operations.

Maintenance planning

Tunnels are supposed to generate revenue, either in the form of toll fees or in the form of benefits to society, such as helping to generate renewable hydropower. The temporary closing of a tunnel, perhaps for months, to renovate or upgrade it means that during this period it will not generate anything at all. It is, therefore, obvious that this downtime should be as short as possible and that a tunnel that is built to a highquality standard right from the beginning will most likely have fewer closures for renovation and upgrading.


TUNNEL MAINTENANCE

At the same time, this probably means that the initial investments will be higher, so the designer and owner of the tunnel project must find the optimum solution. In most cases, this is a very difficult task as there are many unforeseen events that may arise over a 100-year service life, often the projected service life. It is sometimes even longer. There are, though, tunnel projects that are being decided and built without these considerations. This may be due to political commitments that are forcing the owner to build a tunnel for a purpose that is clearly not economically motivated. Examples of this are some of the undersea crossings in Faroe Islands where the purpose is to eliminate the isolation for a small group of people. There can also be defense strategic motives for placing some functions underground in a tunnel.

Secondary concrete lining

The discussion above will, to some extent, explain why tunnel design varies to such a great extent. In Hong Kong, with its large population on a small land area with lots of road, rail and water tunnels, the society is dependent on the functioning of these arteries. Stops (infarcts) in them cause major costs even for short periods of time. Most likely, therefore, all Hong Kong tunnels are given a secondary concrete lining, although the rock material is mainly of good to very good quality and would stand up for very long periods of time without the extensive secondary lining. In a situation similar to Hong Kong, tunnel owners are prepared to pay a large insurance premium to ensure only marginal downtime. On the other hand, in Scandinavia, also with generally good to very good rock conditions, very few concrete lined tunnels are being built, even when they are located in the large cities. The metro line in Stockholm, for example, has almost no concrete structures in its tunnels apart from the cut and cover types. A minimum shell of 10 cm sprayed concrete (shotcrete) is applied mainly to the roof and equally so in the stations. Some stations are given a width of 20 m. So far, no incidents have been reported over the close to five decades long operations of the tunnels.

Sprayed concrete and diesel hydraulic rigs

In this application, the rigs are bringing power and water as they travel from one heading to another and will spend as little time as possible on mobilization. The headings are not supplied by power and water. There are some figures as to which efforts have to be put into the rehabilitation of these “single lining” tunnels. These figures are provided by the road administration in Norway. The tunnels being studied were built from 1964 to 2000. Rehabilitation means here a major reinstating of the tunnel and not regular maintenance that has to be performed, and those costs are not included. There are 14 tunnels being followed, and the rehab cost is spread over the years that the tunnel has been in operation. The result, as shown in the diagram Figure 1, on the next page is that the annual cost for the rehab is less than 0.5% per year for 10 of the 14 tunnels; in three tunnels the figure is 7%; and in a single tunnel 20%. The conclusion is that the low figure represents what can be achieved if the tunnel design and construction have been performed in a professional way. In the three other cases, mistakes were surely made as the rehab cost is in the magnitude of building a new tunnel. Poor workmanship is not the only reason but, most likely, also a miscalculation of ground conditions. An interesting question, while tricky to answer, is: “Would a secondary concrete lining installed during tunnel construction have prevented


201

Trends in tunneling

Certainly, tunnels that feature a far simpler lining consisting of sprayed concrete, which is then supplemented by fully grouted dowels, require inspections at closer intervals. There is also a need for readiness to cope with support improvement in the short time windows when traffic is low, presupposing that the tunnels’ function can be replaced by alternative routes. There are tools suitable for these types of activities, such as sprayed concrete gears that can operate using limited batches and have very short mobilization time, and there are rigs suitable for bolting that are not dependent on a power supply. These multipurpose rigs, such as the Atlas Copco Boomer E1 C-DH, (see photo) are specifically designed to handle a wide variety of tasks in tunneling.

The Atlas Copco Boomer E1 C-DH is a multipurpose drill rig with self-supporting systems including diesel-driven hydraulics and onboard water tanks.

TUNNEL MAINTENANCE

2010

2005

2000

Year of construction

1995 1990 1985 1980 1975 1970 1965 1960 00

05

10

15

20

25

Rehabilitatation as annual cost percentage (%) of the building cost Figure 1: Tunnel maintenance is often calculated over time, to determine key intervals, with annual percentage costs.

extensive rehab works?” Another question, which can be answered is, “Does the year of construction have any influence on the rehab cost?” The answer here is, in all likelihood, no. It does not appear that the year of construction had any influence. The same type of data is available for undersea tunnels where the costs are essentially higher.

Water ingress

The annual maintenance efforts for tunnels lacking a secondary concrete lining are related to water and frozen water. Starting with water, it can be stated that unless ambitious pre-grouting is made there are always some small quantities of water seeping into the tunnel. This water has to be diverted by drains down to the tunnel invert where it is picked up by sewage lines. Diversion of seepage water is necessary in almost all tunnels except water and sewage tunnels. Dripping of water will cause damage to most installations and any existing traffic. The drains will sooner or later become clogged and have to be cleaned or replaced. During the wintertime in road and rail tunnels, the seeping water sometimes freezes and may result

202

in major quantities of ice that float out onto the road or rail track or that may intrude on the required free space. In those cases, tunnels have to be deiced, and this is both a disturbing and costly activity. A concrete secondary lining does not mean that the tunnel is free from the effects of water seepage. In fact, the seepage is probably greater than in an unlined tunnel as mostly no syste-matic pre-grouting has been performed, and most concrete tunnels are drained with the purpose of avoiding the buildup of water pressure that may require a far stronger lining. Here, clogged drains are the same problem as for the sprayed concrete lined tunnels and flushing may be needed. Larger seeping, in the context of clogging, may have an unpredictable impact, and it all depends on the chemicals that are dissolved in the water. The likely higher flows of water may be a threat to the lining itself as the lime may be dissolved. Most road and rail tunnels nowadays have, therefore, an impermeable sheet placed between the concrete and the primary rock support, which will drastically reduce the risk of depleting the strength of the lining. However, far from all tunnel linings are given such protection.


TUNNEL MAINTENANCE

Left: Bolt hole drilling in progress. Right: An engineer checks bolts installed at the Amsteg Tunnel, Switzerland.

Bolts are also exposed to corrosion if they are not properly embedded in cement or resin. Furthermore, the protection may be damaged by movements in the rock mass, and water is given free access to the steel bars. In the case of tunnels that are located under the groundwater table, maintenance engineers need to regularly check the condition of installed bolts. Sprayed concrete ages much like concrete, and the rate depends on the water quality to which it is exposed, the character of the rock, the adhesion capabilities of the sprayed concrete and the long-term deformations and buildup of water pressure behind the sprayed concrete.

Varied impact

Major repair work of damaged concrete linings in metro tunnels has been carried out by building up train sets capable of carrying out the maintenance task without any external supply for a few hours, 7 nights a week. It is also impressive to note that dual-track rail tunnels can be upgraded for higher speed by enlargement of the tunnel section while still allowing traffic to flow normally during the construction work. Naturally, the speed of the trains has to be reduced but that is a minor point in the wider context of tunnel maintenance. ◙


203

Trends in tunneling

Rehabilitation does not necessarily mean that the entire function of tunnels needs to be suspended during the maintenance process. In the case of water tunnels, it is inevitable for these to operate as normal during maintenance work, or otherwise considerable costs will accumulate from a consequential cut-off. An obvious example is the economic damage and loss of power generation that results from cutting off waterways to hydroelectric power plants. A somewhat different example is sewage tunnels, which are generally

rarely full. This may only be the case in instances where the tunnels are also used as stormwater drains. Here, there is, for the most part, a lot of free space under the crown that enables access for maintenance workers. Road and rail tunnels usually have at least one period of some 3–4 hours per day when the traffic flow is low and, as a result, can be cut off without any major disruption. These time windows offer opportunities for rehabilitation work. There is, as mentioned above, equipment that is suited for rehabilitation activities, including drilling, bolting and scaling rigs and concrete spraying equipment.

204

ATLAS COPCO UNDERGROUND CONSTRUCTION – CASE STUDIES

Case studies Road and rail tunnels 206 India's longest road tunnel 212 Beating sonic booms in Naples metro 216 Expanding Norway's road and rail network 224 Pipe roofing at Torrebaso in Spain 228 Cutting out rock for Stockholms's new City Line 232 South Korea's Olympic highway tunnel 236 Below the streets of London: A showcase for sprayed concrete 242 New York's Second Avenue subway line gets underway

Hydroelectric power 248 Harnessing the waters of Colombia 254 In the mountains of Norway: new tunnels for water transfer 260 Continuous loading at Govddesåga 266 Sealing and stabilizing the Boyabat Dam

Water and utility tunnels 270 Potable water for the Malaysian capital

Utilization of underground space 274 The Norsborg depot: A green construction site


205

Nature does not follow the text books! J.S Rathore, Project Director, Chenani-Nashri Tunnelway Ltd

Constructing the longest road tunnel in India, Chenani-Nashri. Here, a Boomer XE3 C at the North face.

Tunneling in the Himalayas

Extraordinary challenges await tunneling engineers high in the Himalayas, one of the world’s most notorious mountain regions. In these conditions, where dangers lurk round every bend, robust and reliable equipment is a given. An upgrade of the famous National Highway 1A (NH1A) in India’s northernmost state of Jammu and Kashmir, will make the present roadway shorter easier and much safer. It will also bring the people of the region closer to the rest of the country. However, the project involves exceptional technical and logistical challenges for the construction engineers installing the tunnels.

206


A typical example is the twin tunnel being driven through the mountains between the towns Quazigund and Banihal, a few kilometers northeast of Jammu. Obviously, no-one would imagine tunneling in this terrain to be especially easy. Danger lurks round every steep bend and the ground is extremely poor. The new tunnel is designed to be 11 m wide, 7 m high and 8.5 km long and is being excavated by

HIGHWAY 1A, HIMALAYA, INDIA

Navayuga Engineering Company (NEC) using a fleet of six Boomer drill rigs from Atlas Copco. As an indication of the difficulties that have to be overcome on a daily basis, NEC Managing Director C. Sridhar points out: “Normally for tunnels this long we would have at least four adits – one at each end and two in the middle. But here we have only two openings to work from, the two portals. This means that all materials and equipment have to travel a distance of more than four kilometers, to and from the only entrances to the headings, and there are additional considerations for such things as lighting and ventilation.” The geology in the area varies continuously through mudstone, siltstone and soft sandstone, and these variations, in turn, demand different types of rock support. Drill and blast technology using the New Austrian Tunneling Method (NATM, sequential excavation and temporary rock support) is the only option. “You can’t use tunnel boring machines in the Himalayas,” says Sridhar. “You can only use NATM, and that means you need Atlas Copco Boomer drill rigs.”

Manual to automatic

In 2011, Navayuga made the transition from direct control face drilling rigs to Altas Copco’s computerized E-series Boomer rigs equipped with Advanced Boom Control (ABC). The six rigs in its fleet consist of four Boomer E2 C two-boom rigs, and two Boomer XE3 C three-boom rigs with high-reach boom consoles and ABC Regular (semi-automatic control mode). Since the E-series Boomer rigs set the pace for the excavation cycles, NEC has opted for a COP CARE service plan for the rigs’ COP 1838 rock drills. This is in order to ensure the highest rate of availability, or as Sridhar puts it, “If the Boomer is idle, everything is idle.” Navayuga chooses to handle all other maintenance, but to provide 24/7 support for the rock drills, Atlas Copco service engineers are stationed at the South and North portals along with mobile service containers.

Selecting the supplier

Navayuga was formed in 2006 and has more than 1 000 engineers working on projects in India and overseas. “When it comes to procuring new equipment, we don’t want to waste time on debating which manufacturer to buy from,” says Sridhar. “We just want a 30-minute conversation, a fair price and an arrangement for when the equipment will be delivered – that’s it.”

Steady progress

In the Quazigund–Banihal tunnels, lasers are used for positioning and setting up the rigs. This is done by lining up two alignment plates on the boom with the laser on the face. The rig “reads” the coordinates to determine where it is in the tunnel relative to the face. The operator loads the drill plan, which has been previously prepared in the office, into the rig’s memory from a USB device, and matches up the projected feed graphics on the display screen. Precise execution of the drill plan is ensured by the rig’s rigid BUT 45 booms, which eliminate deflection and minimize overbreak and underbreak. According to Project Manager P. Sathyarnarayan, the rigs have been performing well and making steady progress. “We have a 99 percent availability rate from the Boomer rigs. Everything is good,” he says. Development of the top heading is maintained 100 m ahead of the bench. The rigs drill one round with a 45 mm button bit in one to two hours, advancing both heading and bench at the rate of 6 m per round in Class 3 rock, or 4 m per round in Class 4 or 5 rock. Holes are charged with emulsion cartridges and mucking is hauled away in 35-tonne trucks. Two excavation cycles are completed in two shifts per day.


207

Road and rail tunnels

He adds that the decision is also based on a few critical factors. “Primarily, we have to be able to trust that the company has expert knowledge so that they are able to advise us of our options. They have to understand the work we are doing as well as we do, not just sell equipment. We trust Atlas Copco for the technical competence of their products, and that also includes service and support.”

The new 8.5 km long twin tunnel between Quazigund and Banihal.

INDIA'S LONGEST ROAD TUNNEL

The Boomer drill rigs are set up using lasers. Each round is drilled with a 45 mm button bit, both heading and bench are advanced at a rate of 4 – 6 m per round.

Rock support is provided by Swellex PM24 rock bolts with a pattern varying from 2, 3 and 4 m, spaced 1.5 m or 2.5 m, center-to-center, depending on rock class. Fiber reinforced sprayed concrete is applied with a thickness of 150 mm. In the Class 4 and 5 rock where the crews encounter weathered sandstone and clay with quartz, a 25 mm primary coating of sprayed concrete is applied. Lattice girders are used for additional support as needed. According to Sathyarnarayan, no convergence has been noted and the project is on schedule with both tunnels expected to be completed by the end of 2016.

Longest road tunnel in India

Traveling on NH1A is an ordeal at the best of times. The single-lane, narrow and winding road crosses some of the steepest, most treacherous terrain in the world and becomes especially difficult to navigate between Srinagar and Jammu – an arduous journey that can take up to 12 hours All that will change when it becomes a four-lane highway, which – together with several tunnels, will reduces the total traveling time to five hours. The twin-tube tunnel being built between the towns of Chenani and Nashri is especially interesting. At 9 km long, it will be the longest road tunnel in the country. The conces-

208


sion was awarded to Chanini-Nashri Tunnelway Ltd (CNTL), a subsidiary of IL&FS Transportation Networks Ltd. G. Vishwanathan, IL&FS’s Managing Director and J.S. Rathore, Project Director of CNTL, point out that the new alignment will cut 30 km off the distance between the two towns. Together with a parallel escape tunnel and cross passages, the job amounts to a total of 19 km of tunneling. “Tunneling in the Himalayas is difficult and the Chenani- Nashri tunnel is no exception,” says Rathore. “The mix of geological formations here leads to a lot of stressing and cracking of the rock mass. It’s full of surprises. Nature does not follow the text books!” IL&FS Transportation Networks Ltd. (ITNL) is one of India’s largest private sector BOT (build-operate-transfer) road operators. The company is engaged in developing, designing, operating, maintaining and facilitating surface transportation infrastructure projects in 18 states in India and four other countries. Its objective is to transform India’s road systems and, thereby, drive economic growth. Coupled with this, ITNL exercises a broad social responsibility (Parivartan) program through which it provides education facilities and support for communities along the highways it builds. This tunnel is also being excavated by NATM and IL&FS has awarded the contract to Leighton Welspun Contractors India Pvt. Ltd on an EPC basis using a fleet of seven Atlas

HIGHWAY 1A, HIMALAYA, INDIA

Thirty operators learned to operate the Boomer drill rigs from scratch after undergoing the Atlas Copco Master Driller program.

Copco drill rigs – four Boomer XE3 C with ABC Total (fully automatic) and three Boomer E2 C rigs with ABC Regular (semi-automatic). Vassilis “Bill” Poulopoulos, North Portal Project Manager, says: “Progress all hinges on one thing – the pace of the face drilling rigs. If the rigs stop, everything stops. Our crews have the excavation cycle down to 10 to 12 hours and we are improving steadily. We are looking for three blasting rounds per day with two 12-hour shifts and I’m certain we will achieve it.” The tunnel enters and exits the mountain at an elevation of 1 200 m. When complete, it will be 14 m wide and 10 m high. A 6 x 6 m escape tunnel is also being built alongside the main tunnel where Leighton is using Atlas Copco Häggloader 10HR-B loaders for mucking out into 35-tonne trucks. Cross passages will connect the main tunnel to the escape tunnel every 300 m for pedestrians and every 1 200 m for emergency vehicles.

Precision essential

Poulopoulos adds: “This rig has been used at the South Portal to verify what we expected to find in the rock mass. The escape tunnel runs ahead of the main tunnel so the rig is used for probe drilling, checking to see that the rock ahead is what we anticipate.”

Master Driller training

To meet its goals, Leighton has developed a skilled drilling crew with the help of the Atlas Copco Master Driller training program. Three months prior to the project and before ever seeing a production drill rig, 30 trainee operators were able to complete all three levels of the course (bronze, silver and gold) using an Atlas Copco Boomer drill rig simulator. It took at least 15 days to complete so the simulator was on the site for three months to ensure that all drillers were sufficiently trained. Lasers are also routinely used for setup at the face. A single Boomer E2 C operator can set one boom in place, start drilling, then turn his attention to the second boom, continuing back and forth throughout the round. The operators are able


209


The rock consists mostly of sandy shale, mudstone, siltstone and soft sandstone, and drilling precision is of the utmost importance to avoid the extra costs associated with underbreak or overbreak. Konstantinos Bastis, South Portal Project

Manager, confirms that this is where the automated features of the drill rigs are proving their worth, citing the MeasureWhile-Drilling (MWD) function on the Boomer XE3 C as an example.

INDIA'S LONGEST ROAD TUNNEL

to drill 100 holes over the 42 m 2 escape tunnel face in just 1.5 hours. The Boomer XE3 C with ABC Total, drills the 76 m 2 main heading with its drill pattern of 152 blast holes in 1 hr, 45 min. Its precision has even allowed Poulopoulos to optimize the drill plan down to 130 holes. “I have an advanced piece of equipment,” he says, “and I am going to exploit it to its full potential.”

Excavation and rock support

The main tunnel is excavated in two levels with the Boomer XE3 C covering the 6 m top heading as well as the 4 m split bench. Excavation of the escape tunnel is being advanced 200 m ahead of the main tunnel and the Boomer E2 C drills the entire face. Blasted rounds range from 2.5 m to 4 m. At the South Portal, rock support is used to assist natural rock convergence which must be less than 2 mm per month. Rock reinforcement consists of two rows of 5 m Swellex PM24 rock bolts, eight in one row and nine in the next. The rows are spaced 2.5 m apart where no convergence is noted. Where convergence is noted, the rows are set 2 m apart. The rockbolt holes are drilled with the same 51 mm bit used for the blast holes. Two bolts are installed in the benches, one on each side. In the escape tunnel, 5 m Swellex PM24 bolts are installed in two rows, the first row with six bolts, the second with seven. Fiber-reinforced sprayed concrete is applied in two overlapping stages to a thickness of at least 150 mm. The first 50 mm is applied immediately after bolting. Setup time is fast enough to provide almost immediate support. Poulopoulos says that with proper scaling and bolting, the 50 mm fiber-reinforced sprayed concrete enables them to progress at a good pace safely, saving them the extra step of bolting up mesh. The second layer of 100 mm sprayed concrete overlaps the initial 50 mm layer during the next advance and provides the support until the permanent lining is installed. In this way, convergence during excavation has been kept to a minimum without compromising on either safety or progress. Lattice girders are used wherever movement is anticipated and will become an integral part of the final tunnel lining. Poulopoulos concludes: “We are in a remote location here with great hardship and logistical difficulties. But we will succeed because we have the best people in the right places. Atlas Copco is doing a good job of supporting us and we challenge each other to achieve excellence every day.” The 9 km long Chenani–Nashri tunnel is being driven successfully in treacherous terrain.

210


Both tunnels are on schedule to meet their 2016 completion date. ◙

HIMALAYA, INDIA

211



The Atlas Copco raiseborer was a very good choice. Paulo Foppiani, Managing Director, Icotekne

To tackle the effect of sonic booms from passing trains, tunneling engineers in the Naples subway have installed a series of horizontal openings using raiseboring.

Relieving the pressure

in deep tunnels

A new mass transit project in Italy had to be restructured for difficult ground and heritage considerations – but a decision to go deeper presented a new and unexpected challenge. The great Italian city of Naples is as fascinating below ground as it is on the surface. For example, several of the city’s subway stations also function as galleries, displaying inspiring works of art that pay tribute to the city’s rich history. Adding to this cultural experience is the extra high comfort and low noise levels on Line 1, the latest extension to the city network, which was opened to the public in 2013.

212


This new twin-tube alignment is considered a model of unique design, but when it was first conceived, the intention was to construct it at the same depth as the existing network. However, it was soon found that this was not a viable option due to loose ground conditions, as well as a number of sensitive archeological sites and historical buildings along the planned route. The solution was simple – go deeper.

NAPLES METRO, ITALY

Figure 1: Relieving the pressure: As a subway train speeds ahead through a tunnel it thrusts a wall of air ahead of it and pulls air in behind it, known as the "piston effect". The air escapes via ducts along the tunnel wall , eliminating sonic booms and potential disturbance to installations.

A different challenge

Constructing the openings

Still, it wasn’t the pressure or the boom that concerned the Neopolitan engineers the most but the resulting vibration that could potentially disturb the stability of the subway platforms, stations and other facilities and installations.

First, the area around the perimeter of each opening was cemented, chemically grouted and then reinforced with rock anchors. Next, an Atlas Copco Robbins 53RH C raise drill was used to drill a horizontal pilot hole of 311 mm in diameter. The machine’s reaming head, which was raised into place on a special trolley, was then fixed to the drill rod and back-reamed, reaming up the hole to the desired diameter of 3.5 m. Lastly, the openings, which varied in length from 5.5 m to 7.5 m, were PVC (Polyvinyl chloride) sealed and lined.

At the planned depth, it was estimated that the tunnels would be subjected to an average pressure of 3 bar (43.5 psi, 300 KPa) and that this pressure would have to be dissipated somehow in order to be safe. The solution was to construct a number of horizontal openings, strategically placed between the two parallel tubes, that would mitigate the piston effect by enabling the air to escape (see Figure 1).

Cuttings were removed by suction using the Leonardo system (modular vacuum suction system) devised by the Francesco Gerotto Company. The Pozzie Martinenghi Company sealed the bores with sheets of PVC, heat-sealing and connecting them to the ashlar (rectangle stone) linings of the line tunnel. The final lining in reinforced concrete, complete with unions to the ashlar linings of the two tunnels, was completed by

It was decided that the extension could be located at a depth of 30–40 m below ground level and 20–30 m below the groundwater table. But at this depth, a design challenge of a different kind emerged. In most underground, high-speed rail tunnels, trains passing through thrust a wall of air ahead of them and also suck in a torrent of air behind them. This creates a vacuum known as “the piston effect” that, in turn, can also create a type of sonic boom.

For this application, contractor Sudmetro, working with geotechnical specialist Icotekne, opted to use raiseboring technology.

213



BEATING SONIC BOOMS IN NAPLES METRO

Raise drilling versatility: Tunneling engineers use an Atlas Copco Robbins 53RH C raiseboring machine to install a series of openings that will relieve the air pressure inside the new subway that runs 30–40 m below the city of Naples.

Cipa, a specialty company that has also worked on the Naples subway project constructing connecting ducts between the line tunnels and inter-route ventilation shafts. Lastly, the bolted ashlar linings were resurfaced by removing the bolt heads and the final sealing was completed. The Atlas Copco Robbins 53RH C raiseborer has an installed capacity of 255 kW, a maximum reaming thrust of 3 350 kN and a maximum torque of 156 kNm. The drill rod is 286 mm in diameter and 750 mm long, while the reaming head, which weighs 12 tonnes, is equipped with 18 cutters.

the danger of falling rock, fumes in the presence of operators in the hole while the work is underway.” The new Line 1, which is known as Metro dell’Arte, runs from Dante Station to the Garibaldi Central Station where it links up with Line 6 to form a ring linking strategic areas of the city with the city airport. Part of the line runs along the coast of the Bay of Naples and parallel to the ancient city wall. Construction in this archaeologically rich area has uncovered many artifacts, which will eventually be on display in the new subway.

Vittorio Manassero, Technical Director of Icotekne, confirms: “These openings connect the two main tunnels and are intended to mitigate the piston effect caused by the passage of subway trains.”

Both Line 1 and Line 2 cross problematic areas, such as loose soil that required considerable reinforcement. Archaeological sites and buildings in the area also had to be well protected. Going deeper was, therefore, the best option.

Paulo Foppiani, Managing Director of Icotekne, adds: “The Atlas Copco raiseborer was a very good choice for this job. Apart from the excellent technology that makes it easy and fast, it is also good from a safety point of view as it eliminates

Besides raiseboring technology, the ground was reinforced through freezing and injection techniques and by utilizing Vertical Shaft Machine (VSM) technology, or mechanized vertical wells. ◙

214


215



With the tunnel profiler and rod handling system, we only need two operators on site for drilling. Christian Mikkelsen, Project Manager, Veidekke Entreprenør

Norway's road and railway network is being upgraded, giving rise to a number of new tunnel projects. Among them are the 3.8 km long Ulvintunnelen, the 200 m long Morstuatunnelen and the 3.3 km long Morskogstunnelen, shown here.

Developing Norway’s

road-rail network

Transport tunnels increase as the land of the fjords continues to expand its connectivity. Modern drilling technology is a prerequisite for success. For many years Norway has been investing in high-speed transport links, combining road and rail networks to make travel quicker and easier, in many parts of the country, with its rugged mountains and famous fjords. These days the projects tend to be on a smaller scale rather than constructing entire routes but tunnels are playing an ever-increasing role, particularly in the construction of new highways.

216


One of the largest of these involves a 21 km stretch of the E6 highway in combination with a 17 km stretch of the Dovrebanen railway, located about 100 km north of Oslo. The E6 project, known as Fellesprosjekt, involves an upgrade of the existing road between Gardemoen and Biri and a rail upgrade of a single track line on the Dovrebanen railway which runs between Eidsvoll and Hamar. The E6 route extends over 3 140 km and runs from Trelleborg at the southern

FELLESPROSJEKT, NORWAY

tip of Sweden and then northwards, linking Malmö and Gothenburg, all the way to Oslo and up through the whole of Norway, ending at Kirkenes on the Russian border. The Dovrebanen also heads from Oslo north through Hamar, Lillehammer and Dombås, and on to Trondheim. In the future, with a double track along the whole route, the journey time for passenger trains between Oslo and Hamar will decrease by one hour, and the number of departures can be doubled with fewer delays. The whole project, commissioned by the Norway National Rail Administration (Jernbaneverket) and National Public Roads Administration (Statens Vegvesen), incorporates three main construction contracts and another for railway technology valued at about EUR 1.4 billion.

Drilling on multiple faces

The Morskogstunnelen highway tunnel comprises twin bores with cross sections of 75 m2 and two lanes each. The highway tunnel bores run parallel to each other with safety cross-passages between them at 250 m intervals. The Ulvintunnelen and Morstuatunnelen rail tunnels have a 125 m 2 cross section to accommodate two parallel tracks in one bore, replacing the current single-track route with a less tortuous route of higher capacity. Apart from the complexity and size of the projects, the conditions are fairly standard for Norway, including hard rock with average-to-good structure. Early excavation at the south portals showed some poor quality rock, although this is not expected to last long into the advance. Tunneling commenced on five faces from all four portals of the highway tunnel and from the northern portal of the rail tunnel. The total amount


217


The central Fellesprosjekt (FP2) contract, worth NOK 1.65 billion (EUR 224M - USD 290M), was awarded to a joint venture consisting of Veidekke Entreprenør (60%) and Germany-based international contractor Hochtief Solutions (40%). This involves a 3.3 km long twin-bore highway tunnel (Morskogstunnelen) and two railway tunnels – the 3.8 km long

Ulvintunnelen and the 200 m long Morstuatunnelen. Most of the tunneling is being carried out by Veidekke and the cast-inplace tunnel concrete by Hochtief. Consulting and design engineer is Norconsult.

EXPANDING NORWAY'S ROAD AND RAIL NETWORK

Figure 1: Three complex tunnels within FP2 have been driven along the shores of lake Mjøsa, the largest lake in Norway, using the drill and blast method.

of rock excavation from all of the tunnels is estimated at 800 000 m3 of solid rock. In addition to these main tunnels in the central section of FP2, the E6 highway works also includes twin bores, 650 m long, for the Korsluntunnelen, and twin bores, 700 m long, for the Espatunnelen.

The contract is operated on a two-shift-per-day basis for 5 ½ days a week. This means 0600 to 0200, Mondays to Thursdays, 0600 to 2300 on Fridays, and 0600 to 1600 on Saturdays, plus maintenance tasks on Sundays.

On the Dovrebanen rail route, in addition to Ulvintunnelen, there is the 620 m long Molykkjatunnelen and the 200 m long Morstuatunnelen, the latter also being within FP2. These all complete the project route between Minnesund in Eidsvoll at the south end of the Lake Mjøsa to Kleverud in the Stange commune. Lake Mjøsa is the longest lake in Norway and the second deepest in Europe, stretching from Minnesund to Lillehammer.

Advanced excavation equipment

In addition to the running tunnels and highway tunnel crosscuts at 250 m intervals, the access tunnels are being retained as escape routes from the rail tunnel. These comply with the minimum required escape route interval of 1 000 m for the rail tunnel. There will be two access tunnels, 500 m long, at the southern end of the tunnel. Towards the north portal there is a connection between the rail tunnel and highway tunnel bores for the same purpose. Reduced spacing between excavations here also requires extra ground stabilization by grouting.

218


When the Veidekke-Hochtief joint venture won the contract, the company decided to rely on a fleet of six Atlas Copco Boomer XE3 C face drilling rigs to excavate the tough rock conditions and to facilitate a systematic grouting program. In view of the tight project schedule and the ‘critical path’ nature of the main tunnel construction, the drill rigs are backed up by special service arrangements for the consumables, including a new bit grinder, servicing for 24 Atlas Copco COP 3038 hydraulic rock drills, and the provision of onsite parts stores for the rigs themselves. All drilling consumables are supplied by Atlas Copco Secoroc. The Boomer XE3 C rigs are all equipped with COP 3038 high-frequency hydraulic rock drills. These offer unprecedented penetration rates in all types of hard rock, and with a pressurized housing and close mating surfaces, there is


reduced internal contamination. Until the development of a 40 kW rock drill, the COP 3038 was also the most powerful drill available from Atlas Copco. Veidekke’s Works Foreman reports that site visitors from both Australia and South Korea were impressed with the performance of the COP 3038.

Rig Control System

All rigs have the advanced Atlas Copco Rig Control System (RCS), much of which have been based on field experience and customer requirements. This modular system is based on PC-compatible components and powerful microprocessors. The modular design allows easy upgrades and option inclusions. Data exchange between different rig subsystems and functions is fast, accurate and reliable. The comfortable operator’s cab and ergonomic positioning includes twin display consoles to display the drill pattern, profile scanner and other rig operating function values. The drill pattern comprises 130 blastholes for the highway tunnel drives. Both the highway and rail tunnels utilize 5 m deep parallel hole cuts. Most holes are 48 mm in diameter except for four of the nine central relief holes, which are 54 mm in diameter. An exception is the use of 54 mm button retrac bits in weak rock for easier drilling in broken ground. The rock to be excavated is typical of southeast Norwegian bedrock consisting mainly of plutonic gneisses which can be exceedingly hard and abrasive when there is a high quartz content. Drill penetration rates, with optimum grinding of the button bit inserts, average 2.8–3.0 m/min, although this can vary between the tunnel faces and so different rock types. There are two rows of peripheral holes at closer spacings. These are more lightly charged to achieve a smooth profile with no overbreak. The blasting agent is a bulk emulsion (Orica SSE) mixed on charging for sensitizing in the holes to form an explosive. The efficient charging allows blasting to be carried out only an hour after drilling of the face has been completed, subject to environmental restrictions on blasting times. Use of sitesensitive emulsion reduces security requirements and greatly eases materials handling. The drill rigs play an important role in excavation accuracy with features such as rigid, rectangular-section BUT 45 booms of the E-series, Advanced Boom Control (ABC) and profile scanners. The new booms also provide faster positioning, greater carrying capacity and higher bracing force.

board computer controls drilling of the round according to a predetermined drill pattern. Rolf Blomberg, Atlas Copco Business Line Manager for Underground Rock Excavation products in Norway, emphasizes the importance of the advanced instrumentation installed on the rigs. This includes the Atlas Copco Tunnel Profiler to check on the excavated profile for any under- or over-excavation. It gives the rig operator an effective feedback on drill pattern accuracy and correct hole charging. General accuracy on a scanned surface is <5 cm. The use of the Atlas Copco Tunnel Profiler is directly related to accurate directional control of the rig using the rigs’ laser-based guidance and drill-hole pattern system. Veidekke Project Manager Christian Mikkelsen comments: “It’s very efficient. The rig operators can use it, so this saves money on surveying. We advance to around 70 m away from the last survey point (as backsight). Beyond 100 m the laser spot becomes too large for accuracy.” Mikkelsen says he believes this is practically the ultimate in drilling performance for his crews. Drilling teams, including support workers, comprise four for a single-face drive (in the


219


One of the advantages of ABC is to facilitate accurate multiboom operation by one operator, thus speeding up the whole drilling process. The ABC ‘Total’ option is employed for the highest level of automation to allow the round to be drilled automatically under the supervision of the operator. The on-

A drill bit grinder from Atlas Copco Secoroc is used on site, with 4 to 5 hours of grinding every day, to optimize the operations.


The COP CARE agreement provides reassurance to the contractor of continuous drill availability and optimized performance. In exchange Veidekke-Hochtief pays a fee per meter drilled, and Atlas Copco supplies all necessary drill service parts, proof of services carried out, and other actions needed.

Rock support

The project consultant, on the basis of rock quality, stresses, tunnel section, and rock type, decides the type and amount of rock support in the tunnel. Apart from the weakness zones, jointing is the main structural consideration. As a result of these determinations, plus the nature of the weakness zones, the tunnels are divided into seven rock classes based on the mapped Q-value for the rock, a system first developed in Norway.

Using a fleet of Atlas Copco Boomer XE3 C drilling rigs, the highway tunnels are advancing at a rate of 20–30 m per week.

Ulvintunnelen) and four or five for the twin-bore faces of the Morskogstunneln.

Onsite support

The Atlas Copco support for the project involves a number of on-site facilities, including a workshop for drilling rigs, a drill steel container, another container acting as a bit-grinding and drill maintenance workshop, as well as various parts storage containers. Drill consumables supplied by Atlas Copco Secoroc are also serviced on site in a special workshop adjacent to a storage container. Here one operator is employed full time using a new Atlas Copco Secoroc Grind Matic grinder on all the reusable drill bits for the six operational Boomer rigs – equivalent to 4–5 h of continuous grinding per day. Coupled with a delivery service, this avoids removing operators from the drill face to carry out bit grinding. The Atlas Copco COP CARE service and preventative maintenance package for the COP 3038 drills is based on a 250 h service interval for the 24 units. There is a technician on site to replace any defective drills and to carry out regular servicing. The drills are replaced on the rig and brought to the special surface workshop for a full ‘strip-down’ overhaul by the Atlas Copco technicians who are onsite nearly every day.

220


The primary support for all tunnels is a combination of sprayed concrete and rockbolts with various reinforcement and ground support depending on the rock classification and according to predesigned patterns. Typical roof rock bolting, using the Boomer XE3 C rigs for the drilling of holes prior to bolt installation, is of 1.0–2.5 m, center-to-center. Then sprayed concrete is applied to a total thickness of 80–150 mm. In the Ulvin rail tunnel (Ulvintunnelen) this is considered permanent support until the final cast in situ lining is installed. This avoids having to include another step in the lining/support process. In addition to the support installed after excavation, a program of systematic pre-grouting is required in about 17 percent of the tunnels’ length. Other grouting depends on the occurrence of any large groundwater leakages, which should be identified in advance by probe drilling of expected zones of weaknesses. Veidekke’s Niklas Hallström explained, “It’s important not to use bolts longer than 5 m, otherwise it will cause you to puncture the grout fan.” The result of creating such a puncture would be to create a possible passage for groundwater. Rock excavation of the location of the two technical rooms in the Morskogstunnelen, although of good quality, has to be carried out with particular care as the two bores are too close to leave support pillars of rock. The rooms, each of around 90 m 2 floor area, are to be built as three parallel sections with a total span of 30 m. Successive support structures will be established between the caverns so that the rock can be removed under safe conditions.

Grouting

Before installing the final lining but after blasting, the contractor has to ensure that the ground is structurally sound and impervious. There are several weak zones along the tunnels, varying in terrain and depth and categorized into three


The Ulvin rail tunnel (Ulvintunnelen) has a cast in-situ segmental lining to ensure durability and safety. A total of 150 000 m³ of cast in situ concrete is used for the operation. A synthetic membrane (white) is applied and placed behind the concrete lining.

categories depending on the expected size at tunnel level. Dips of these are uncertain.

support. Use of the same drilling rig saves on additional plant investment and causes less disruption to tunnel advance rates.

Waterproofing, or drainage, is important for both the structural durability of the tunnels and environmental consequences. The water table over the tunnel routes can be high, and there are several wells or springs on the route, including some artesian. An assessment of the possible consequences of underground water leaks includes the nature of their vulnerability, private water supplies and the geometry of the rock structures. However, it has been found that no habitats are considered vulnerable to lower groundwater.

For ground stabilization, the usual design requirement is for 17 holes, each 21 m long, to be drilled at an angle of 10–15 degrees from the tunnel alignment (depending on hole length) in a fan pattern, or as directed by geotechnical experts to any weak or disturbed zone. The normal fan pattern ends 5 m from the tunnel periphery. For where special waterproofing measures are required, a total of 44 holes is drilled so that the grout can seal up all water passages in joints, fractures, etc. Project Manager for Veidekke Entreprenør, Christian Mikkelsen, explained: “Grout holes normally need to start 30–34 cm outside of the blasting profile and at the end of the hole be at least 250 cm outside.”

Private wells will be monitored during construction for possible drainage through the tunnel. All rigs also have the Atlas Copco Rod Handling System (RHS) installed on all three booms, which is particularly valuable on this project with its high proportion of grouting work using the same Boomer XE3 C rigs that are used for blasthole drilling.


221


Grouting holes are required in predesigned tunnel stretches for ground cover support, stabilization where required, and waterproofing to comply with groundwater extraction regulations. On some parts of the routes there is only 4-6 m of cover over the tunnel, so the grouting is needed for additional roof

Grouting itself employs two Atlas Copco Unigrout grouting platforms with four grouting lines from each unit. These inject fine, cementitious grout with additives including stabilizer and water-reducer (to increase viscosity) according to the required properties of the grout on injection. Veidekke owns the world’s largest standard, mobile grouting unit with the Unigrout. The rig assembly combines grout mixing using Cemix units, pumping, and recording of grout injection procedures. The automated plant can produce up to 10 m3


of grout per hour with a control system that enables onsite mixing of various grout ‘recipes’ according to site requirements. From time to time, grouting may necessitate certain changes to the drill and blast patterns, in order to avoid drilling into any grout-filled fractures ahead of the face. However, this creates no problem for the Boomer rig as its ABC control system is easily and quickly adjusted to a new drill plan taking the repositioned holes into account. The overall rate of progress in the highway tunnels has been affected by required grouting and rock conditions but through 2013 has averaged around 20–30 m per week.

Permanent Lining

The permanent linings for the two tunnels are different in design with Hochtief carrying out precast concreting in the Morskog highway tunnel (Morskogstunnelen), whereas the Ulvin rail tunnel (Ulvintunnelen) has a cast in-situ segmental lining that is not very common in Norway. This is understood to be part of a program by Jernbaneverket to improve the quality of rail tunnel linings, especially controlling water ingress, which can be a major problem in winter with the creation of icicles. At emergency lay-bys, some of which are also locations of ‘technical rooms’ for switchgear, special precast concrete element are to be used in the walls with polyethylene foam fire protection installed in the room and secured with sprayed concrete. Use of precast concrete lining requires particularly accurate drill-and-blast. Otherwise extra grout would be needed to fill the annulus behind the lining extrados. Accuracy is also important to save on materials usage. Even when in the rail tunnel, the finished profile will be achieved with cast in-situ concrete, excavation accuracy is important not only to ensure concrete use is economical, but also to ensure that the first support layer of sprayed concrete is also accurate without sharp protuberances of under-excavated rock. The first layer of 200 mm of sprayed concrete should be smooth to form a good base for the membrane to be installed to drain away as groundwater seepage. A total of 150 000 m 3 of cast in-situ concrete will be used in the Ulvintunnelen lining. “MWD (Measurement While Drilling) documentation is required by the project client to check on any drilling difficulties and geological anomalies, as well as grout hole positions,” explained Blomberg. “It is an online system by which data can be downloaded from the rig instrumentation by wireless connection to be available in real time.”

222


At this time, the data is transferred using a memory stick with downloading on the drill rig, but Mikkelsen reports that wireless communication in the tunnels is under investigation.

Environmental Considerations

Throughout the project, the joint venture contractor is obliged to pay due consideration to the environment for both social and operational reasons. Normal traffic on the E6 and single-track railway will continue until project completion and transfer of traffic flow. Normally the sites are located away from the existing routes to avoid any disruption, although the breaking of ground at the Morskogstunnelen south portals caused some inevitable delays to traffic. Social considerations include monitoring for drilling and blasting vibrations, although there are few dwellings within the likely zone of influence of tunneling. “There are only about 30 residences on the route,” says Mikkelsen, “ but on the other hand this could mean that any issue gets more personal.” As previously mentioned, only quiet maintenance tasks are carried out on Saturday and Sunday evenings. Blasting operations are restricted according to scheduled rail traffic. The allowable blasting times, therefore, vary between five minutes and several hours. Highway traffic must be halted during blasting, and this is limited to 20 minutes. As already mentioned, private wells in the rock will be monitored for the possible effects of construction, including drainage. If any are drained, the project owner has established a program for replacement.

Completion

This advanced and complex project is on a tight schedule. After a start in April 2012 construction of the road tunnel bores are scheduled for completion in November 2014 (2.5-year construction period) and the rail tunnel for autumn 2015 (3.5-year construction period), with full operation in the following year. Tunneling should take just a year. So far the contractor believes the decision to invest in advanced drilling rigs, including their featured instrumentation, has been very justified. “Working has been very good,” reports Mikkelsen, “with only one problem with the computer on one rig. The control system with tunnel profiler is definitely needed both for the grout injection program, and for efficiency of drilling. Other features, such as the rod handling systems, are also valuable. It’s safer because the drillers don’t need to go in front of the rig to change drill rods. It also avoids having an operator in an atmosphere with oil fumes. With all these procedures we only need two operators on site when drilling.” ◙

223



Pipe roofing is the fastest way of stabilizing rock. Andoni Bonacchea, Technical Officer and Purhasing Manager, Geotunnel

A special reinforcement method known as "pipe roofing" was used for the Torrebaso railway tunnel in northern Spain. The tunnel crown was stabilized by installing steel pipes in an umbrella pattern.

A simple solution

for poor ground tunnels

Poor quality ground always presents challenges of one kind or another. In Spain, leading tunnel specialists have a simple solution. The Torrebaso rail tunnel may only be 170 m long, but it is a key element of the Spanish railway’s northern network, allowing trains between Bilbao to San Sebastian to travel non-stop in both directions. Located near the town of Amorebieta in the province of Bizkaia, this twin-track tunnel looked like a relatively straightforward task until the construction engineers discovered that the ground was unusually poor.

224


Geotunnel, one of the biggest tunneling specialists in the country, did not have to look far for a solution, however. The company uses Atlas Copco drill rigs for drilling and blasting and used this same equipment together with the Symmetrix system, a patented system of drilling through overburden with symmetrical drill bits and casing, to stabilize the tunnel crown. The Boomer L2 C drill rig was used to install steel pipes or casings in an “umbrella” pattern to provide a presupport canopy ahead of the advance. This stabilization and

TORREBASO, SPAIN

Figure 1: To prevent loose rock from caving in the Atlas Copco Symmetrix method was employed whereby casings are inserted into the drilled holes, creating a support structure, or "umbrella", at key intervals along the tunnel length.

reinforcement operation resulted in the installation of 1 824 m of steel pipes and 35 000 kg of cement. Along the entire length of the tunnel, five “umbrellas” were installed, with one umbrella per tunnel section and an average of 30 pipes per umbrella. Each pipe was 12 m long. A starter pipe fitted with the standard Symmetrix ring bit set was used followed by extension pipes, in this case 89 mm with a 7.1 mm wall thickness, using the Symmetrix P89 system. The pipes were installed at an angle of 4 degrees and spaced 30–50 cm apart. Once installed, they were grouted in place to form a strong canopy around the tunnel crown. Net drilling time for a 12 m pipe averaged 10 minutes, and the total time for installation was 30–40 minutes per pipe, depending on the condition of the rock and other operational factors. As a rule, each installation was perfectly straight.

A favorite method

At the Torrebaso tunnel, Geotunnel operated as a subcontractor within the Corsan Corviam/Balzola consortium. The client was Ute Euba-Iurreta, and the project was commissioned by E.T.S. (Euskal Trenbide Sarea), the housing, transport and public works authority of the Basque administration. Borja Del Palacio, Tunnel Manager Engineer, Geotunnel, says: “We have installed hundreds of meters of pipe roofing around the country, and I have to say Symmetrix is my favorite method. It is fast, reliable and economical, and the quality of the bits and tubes we get from Atlas Copco is very good. “We can also use the same drill rig for pipe roofing as for drill and blast, which means it is not necessary to subcontract this work to a specialized pipe roofing company.” Andoni Bonaechea, Geotunnel’s Technical Office and Purchasing Manager and the man who decided to use the method at the site, says he is especially pleased with the way


225


In this way, more than 10 900 m 3 of rock and soil could be excavated and the tunnel, with its cross-section of 49 m3 and crown radius of 4.56 m, was completed in less than one year. That was in 2011, and today, pipe roofing with the Boomer-Symmetrix combination is a Geotunnel specialty. The

company has installed more self-drilling umbrellas in Spain than any other contractor.

PIPE ROOFING AT TORREBASO IN SPAIN

Figure 2: The Symmetrix system consists of a pilot bit and a ring bit. When using the pipe roofing method, the ring bit is unlocked and left in the hole together with the casing pipe.

things worked out. “Pipe roofing using the Symmetrix system is by far the fastest and most economical way of stabilizing unfavorable rock conditions in tunneling, and we proved it at Torrebaso,” he said. The Symmetrix system has been equally successful in many other countries, including Portugal, France, Sweden, Kazakhstan, India and the Czech Republic.

Complete package

Atlas Copco offers a complete package of equipment for this technology – Boomer drill rigs, Symmetrix Casing Advancement System together with pipes, Secoroc drill rods and Unigrout grouting equipment. The Symmetrix Casing Advancement System is based on the rotary-percussion drilling method and consists of a pilot bit and a ring bit. The pilot bit is attached to the ring bit with a bayonet locking mechanism. Together they drill the hole, which is large enough to allow the casing to advance simultaneously as the hole is being drilled in loose and collapsing ground conditions.

226


During drilling, the pipe itself does not rotate, so there is no need for high torque on the drill rig. A special feature of the system is that flushing is carried out through the annulus between the casing pipe and drill pipe, ensuring high efficiency with minimal damage to the adjacent formation. When the hole is complete, the pilot bit is unlocked from the ring bit and withdrawn through the casing pipe together with the drill pipe. The casing pipe (and ring bit) is permanently left in the ground. The system is designed for installing casings with a diameter of 76.2 to 1 220 mm (3–48 inches). The method is used worldwide for a variety of applications, including foundation drilling and well drilling, in addition to tunneling. For the Torrebaso tunnel application, which required tophammer drilling, the available diameters of the casings were 76.2 to 139.7 (3–5 ½ inches). The pipe roofing and forepoling techniques are widely used by Spanish contractors both in the local market and on international projects. Geotunnel reports that the Symmetrix system is one of the most flexible solutions for reinforcement work. ◙

227



Wherever vibrations are a problem, the diamond wire machine is the perfect solution. Leif Arvidsson, Project Manager, Norrbottens Bergteknik

The City Line railway project in Stockholm, Sweden, extends below residential urban areas. This construction site is only a few meters away from St. Matthews Church, a sensitive building dating from the 19 th century.

Cutting into the future Diamond wire cutting machines, once seen only in rock and marble quarries, are rapidly appearing on urban construction sites where blasting is out of the question. The city of Stockholm, Sweden, is a typical case in point. With an increasing number of infrastructure installations now being built in highly populated urban areas, the possibility to blast underground is becoming increasingly limited. These days, residential buildings, churches, schools, designated heritage sites, utility tunnels, roads, subway tunnels and rail links are just a few of the many sensitive urban structures that make it impossible, or unacceptable, to use blasting techniques for construction. Instead, contractors have to find other alternatives. One of the most common blast-free solutions available today is wire cutting, a technology that is both environmentally friendly and highly versatile.

228


Wire cutting machines can be used for a wide variety of installations ranging from ventilation, elevator and escalator shafts to cable, road and railway tunnels well as for shaping rock walls close to sensitive structures, and much more.

The City Line solution

The new City Line railway in Stockholm, the capital of Sweden, is a typical example. The city is built on 14 islands and is currently undergoing a major upgrade of its commuter transport system, which is scheduled to be completed by 2017. The new network will double the passenger capacity and improve the overall flow of Stockholm’s public transport system.

CITY LINK, SWEDEN

On the island of Riddarholmen in Stockholm, diamond wire cutting was used for a tunnel section in the City Line construction project. The technique was chosen in order to avoid vibrations and potential damage to the foundations of historical buildings.

The project involves the construction of 6 km of new tunnels, some sections of which are under water, and a number of new passenger terminals. Moreover, the new tunnels run through the very center of the city just meters from existing subway lines and directly below a number of historical buildings, many of which are listed as heritage sites. Understandably, this scenario poses some difficult challenges for the tunneling contractors. For example, on the island of Riddarholmen, large sections of rock have had to be removed at a depth of 3–6 m below the surface to make way for a new tunnel section, but without putting the foundations of nearby structures at risk.

Fastest in the world

The solution was a diamond wire cutter from Atlas Copco, one of the world’s leading producers of wire cutting machines. Appropriately called SpeedCut, this model operates at the rate of 45 m 2/h and is described as the fastest rock cutter in the world.

This system enables constant tension to be maintained on the wire irrespective of a possible surge in water flow, a drop in electricity supply, non-homogeneous material being encountered or other variable conditions. The operating panel interface and connection cable are easy to handle and allow the machine to be controlled from a safe distance. The SpeedCut cuts both vertically and horizontally and close to ground level. Furthermore, its main flywheel can be rotated 320 degrees, which means that it can perform parallel cuts with a maximum distance of 2 m without having to be repositioned. For further detailed information see chapter "Diamond wire cutting" on p. 170.. Optimal performance is assured with full documentation and control of the cutting parameters and cutting processes.


229


The engineers first drilled holes into the rock, either vertically or horizontally. Then the diamond wire was passed through the holes and the ends joined together to form a continuous

loop. Next, the wire was fitted onto the SpeedCut’s flywheel, which rotates at speeds of up to 45 m per second. During cutting, an electronic control system moves the machine backwards, allowing automatic tensioning of the wire. This innovative system makes it possible to combine high cutting speed with low wire consumption. The system also employs a groundbreaking load cell that reads the wire tension every second.

CUTTING OUT ROCK FOR STOCKHOLMS'S NEW CITY LINE

Traditionally used in the dimension stone industry, the diamond wire cutting machine is capable of cutting out large slabs of rock without vibrations. This makes it highly useful on sensitive work sites in cities.

Working parameters, such as cutting time, wire performance and error code lists, can also be downloaded to a computer via a USB memory stick or using WLAN.

Eliminating vibration

One of the biggest drawbacks of blasting in any environment is vibration, and for the tunneling engineers on the Riddarholmen project, that was a major factor in the decision to use the SpeedCut. As Leif Arvidsson, Project Manager for contractor Norrbottens Bergteknik, explains: “Wherever vibrations are a problem, the diamond wire machine is the perfect solution. We were very happy with the way the SpeedCut performed. We didn’t break any wires and downtime was minimal.” Slicing through the rock at a rate of 7–8 m 2 per hour, the SpeedCut completed its task in removing slabs of typical Swedish granite within two weeks and without disturbing any other subsurface installations or surface buildings in the vicinity. At another site in a densely populated area north of the city center, Norrbottens Bergteknik was also engaged to build the foundations of a new subway station entrance that will connect to the City Line via a 60 m long tunnel. Once again, drilling and blasting was rejected due to the disturbance that blasting would involve for residents, as well as the damage that the vibrations might inflict on the foundations of a 113-year-old church , St. Matthews, located just a few meters away. In this case, the SpeedCut machine was used for horizontal cutting of so-called blind cuts, which involves cutting through of a series of tightly positioned drill holes.

230


Andreas Christoffersson, Managing Director of Norrbottens Bergteknik, says the flexibility that the wire cutting technique brings to tunneling makes it an invaluable resource. Another big plus point, he adds, is that the machine is virtually noiseless. “It’s a smooth operation that can be performed even during the night as the noise stays well within decibel limits. The wire makes a buzzing sound during the first incision, but as it works its way through the rock, you barely notice any noise or vibration at all. On top of that, the machine is electric, so there are no diesel engines running.” Under normal operating conditions, the diamond wire lasted for approximately one week, or 200–300 m 2 before it had to be replaced. The most commonly used wire is 11.2 mm in diameter and equipped with 35 diamonds per meter.

Old technology new future

Diamond wire cutting machines are by no means new. They were first introduced in the 1980s and rapidly gained popularity, mainly in the dimension stone industry (DSI) in marble and rock quarries. However, as production levels steadily increased, the technology was developed and refined. With increasing urban construction, tomorrow’s wire cutting machines can be expected to become even more advanced and a valuable feature of every tunneling contractors’ equipment fleet. Similarly, as the demand for safe, quieter and less disruptive construction operations grows stronger, cutting rather than blasting is destined to play an increasingly bigger role for a multitude of auxiliary tunneling tasks. ◙

CITY LINK, SWEDEN

231



Olympic challenge: the raiseboring technique has been used to install ventilation shafts for South Korea's longest road tunnel, Inje Tunnel.

Raiseboring solution for South Korea’s Olympic highway tunnel Two large ventilation shafts for a tunnel through the mountains of Kangwondo, South Korea, are now in place as part of a major highway upgrade for the next Winter Olympics. The Winter Olympics 2018 will be held in PyeongChang, South Korea, and a new highway is being built to enable spectators to travel from Seoul, the capital, to the Olympic area. The new highway will run from Seoul towards YangYang in the east before turning up to an existing southbound road to PyeongChang, drastically reducing the driving time from 4 hours to 1.5 hours.

232


A key element of the project is a new road tunnel in the mountainous region of Kangwondo. Called Inje Tunnel, it is 10.9 km long and is the longest road tunnel in the country. Inje Tunnel is on track to be completed in 2015. Excavation is by drill and blast using the New Austrian Tunneling Method (NATM, sequential excavation and temporary rock support),

INJE TUNNEL, SOUTH KOREA

and while this is a big challenge, the job of installing the necessary ventilation shafts has been an Olympian achievement. SungPoong Construction, South Korea’s leading specialist in ventilation and ventilation shaft applications, was awarded the contract to install two shafts, 212 m and 307 m long. The shafts are placed 4 km apart along the tunnel alignment and have an initial diameter of 3.1 m, which will later be enlarged to 10 m in diameter. Since it was founded in 1989, SungPoong Construction, headquartered in Jechon in the eastern part of South Korea, has specialized in vertical tunnel and ventilation shaft collar applications. The company has also carried out a number of infrastructure construction and civil works projects.

C

H

I

N

A

For this project, SungPoong chose to use an Atlas Copco Robbins 73RVF C medium-sized raise drill designed for raises ranging from 1.5–3.1 m in diameter, accompanied by an Atlas Copco Secoroc Mini Super Base System, which is a modular reamer assembly system. In addition, the package included Atlas Copco Secoroc Magnum cutters, a flanged stinger and 12 ¼ in pilot bit.

Variable speed drive

The Robbins 73RVF C is an exceptionally energy-efficient raiseborer. Its RCS control system provides total control of speed and torque, and built-in break resistors eliminate the risk of backspin. The compressive strength of the rock at this site varies from 200 to 350 MPa with less than competent formations. However, the variable speed drive on the raiseborer optimizes the operating performance, irrespective of the rock conditions. This means that the machine’s drillstring always utilizes its full torque capability. The Magnum cutter used at the Inje Tunnel features the roller-ball-roller bearing system, large carburized bearing races, and an optimal cutting structure for long cutter life.

Seoul

PyeongChang

S O U T H K O R E A

Both of the raises were successfully completed with excellent cutter wear. For the 307 m shaft, one Magnum cutter set consisting of 16 cutters was used, and an inspection revealed that 40% of its service life still remained. For the 212 m shaft, a new set of cutters was used, and 70% of its service life proved to be still available. Kiman Cho, Project Manager for SungPoong Construction, was clearly pleased with these results. “I think the Magnum cutter is amazing,” he commented. “It has a three to four times longer service life than any cutter I have ever used before.”

Figure 1: PyeongChang, the venue for the 2018 Winter Games, is located about 180 km east of Seoul. Motorists will travel on the new super highway to YangYang and turn off at an interchange shortly after emerging from the Inje Tunnel, then head southwards for PyeongChang.


233


After working round the clock to complete the shafts on time, SungPoong’s engineers filed the following work report: • Pilot holes: 37 days (average 14 m/day) • Reaming holes: 47 days (average 11m/day) • Total drilling days: 84 • Total project period, including site preparation and trans portation: 145 days

J

SOUTH KOREA'S OLYMPIC HIGHWAY TUNNEL

The Robbins 73RVF C with a Magnum cutter system, set up on the surface and during reaming for the 212 m and 307 m long shafts.

Project Manager Cho explained that these achievements were due to very few breakdowns, thereby keeping downtime to a minimum. Mattias Calleberg, Atlas Copco Service Engineer, said: “The site preparation on this project was the most impressive I had ever seen. SungPoong Construction has successfully completed two very accurate holes at the Inje Tunnel with good penetration rates and very little downtime. This was in spite of dirty water caused by clay between two layers of granite that affected the bailing pump and several rock bolts that had been left in the tunnel roof. “Normally it is no problem to cut through anchor bolts, but one of these had an anchor plate that we were unable to drill

234


through, so it had to be removed. After that, everything went smoothly.” Expressing his satisfaction with the result, Jinpyo Kim, Purchasing Manager for SungPoong Construction, concluded: “Our team was able to finish this tough job with optimum drilling conditions, despite non-competent and hard rock. This was largely due to the speed and torque control system of the drive motor on the Robbins 73RVF C, which also relieved the burden on the drillstring. Furthermore, the machine was easy to set up and troubleshoot, and this also contributed to increasing the uptime.” ◙

The Magnum cutter system is amazing. Kiman Cho, Project Manager, SungPoong Construction

235



Photo: courtesy of London Underground.

The Tottenham Court Road station upgrade, commissioned by London Underground, will include interchange links to the massive Crossrail mass transit project. With some 10 000 people projected to work across 40 sites, Crossrail is the biggest infrastructure development ever undertaken in Europe.

World class coatings for London tunnels A major upgrade of the mass transit system in London is on track to become an international showcase for state-of-the-art tunnel lining technology. The biggest infrastructure project ever undertaken in a European capital is currently underway in London, and is set to become a landmark in the history of urban infrastructure. London is one of the busiest and most densely populated capitals of the Western world with a population of 8.3 million, and this figure is expected to grow to around 10 million by 2030. It is not surprising then that the ageing London transport system needs to be completely modernized in order to cope with future demands.

236


However, the city is not just making a few minor improvements to its infrastructure. It is investing a staggering GBP 14.8 billion (approx. EUR 18 bn, USD 24 bn) to create a world class mass transit system that is expected to set the standard for 21st century urban development. The local transport authority, Transport for London (TfL), is responsible for implementation of the strategy and management of transport both underground and overground, while

LONDON UNDERGROUND, UK

Photo: courtesy of London Underground.

Atlas Copco’s MEYCO concrete spraying equipment together with Atlas Copco compressors proved to be an excellent combination at the TCR site. The same equipment is now being used to upgrade facilities at the famous Victoria Station, another iconic transit hub, where contractors Taylor Woodrow/BAM Nuttall expect to complete the work during 2017.

Crossrail manages the job of creating the tunneling transport links. Launched in 2009, the project includes 42 km of new rail tunnels, a further 7.7 km of service tunnels and platforms, and the refurbishment of 38 stations, increasing capacity in an east-west direction by some 10%. At the same time, the London Underground subway is undergoing a major upgrade with new tunnels and modernized facilities at dozens of sites across the city that will function as key underground interchanges for the mass transit system.

By early 2014, the project had successfully passed the halfway mark, and despite the enormous complexities and

Benefits and demands

With the expected growth in population over the next two decades, the need for a state-of-the-art mass transit system for London is beyond dispute, but the long-term economic benefits involved for Britain as a whole have also been a driving factor in the decision-making process. It is believed that some 55 000 jobs will be required in the construction phase alone, and when the new system is fully operational in 2018, it will generate at least 75 000 new business opportunities. In addition, it will provide much easier access to employment, education and housing for millions of citizens. Exceptionally high demands have been placed on the design, engineering know-how, technical skills and project


237


The modernization has been designed to transport an estimated 200 million commuters to and from the city every day. As a result, London’s urban infrastructure will be changed dramatically, not only because tomorrow’s Londoners will need faster and more convenient travel possibilities, but also because of the increased opportunities it will bring for commercial development and future economic growth.

challenges of carrying out tunneling and civil works beneath the streets of a major conurbation, with a minimum of disturbance to city life, it has progressed on schedule and, for the most part, on budget.

BELOW THE STREETS OF LONDON: A SHOWCASE FOR SPRAYED CONCRETE

Needless to say, a project of this magnitude and complexity in densely populated London involves unprecedented logistical and technical challenges for the tunneling engineers. In this respect, it is interesting to consider that: • The majority of the Crossrail commuter train tunnels, which are 6.2 m in diameter, are being driven by mechanical exca vation using TBMs (Tunnel Boring Machines) through 55 million year-old clay • Other tunnels will be driven through waterlogged ground beneath and around the River Thames • Noise, dust and traffic diversions for haulage vehicles have to be kept within strict limits so as not to disrupt everyday London life

Makeover for "The Tube"

Against this background, the upgrade work being carried out on the London Underground – commonly known as “The Tube” – is worthy of special recognition. Opened in 1863, it is the oldest metro in the world and an icon in British engineering history. Not only did it enable Londoners to become the first city dwellers in the world to travel underground, its deep tunnels have also provided them with protection in times of war.

Courtesy of London Underground /Crossrail

How the Crossrail TCR station (western entrance) will look: An ultra-modern hub for the demands of the 21st century, due to be opened in 2018.

management involved in every stage, and within this framework, sustainability and safety get top priority. For example: • The majority of all demolition and construction waste has to be recycled • All excavated material has to be beneficially used, much of it being transported to a nature reserve (Wallasea Island, Essex) to be used as landfill • All haulage vehicles have to be fitted with additional safety features and drivers must undergo additional road safety training In the process, a number of groundbreaking auxiliary services have also been created. These include a new training college for apprentices, innovative management systems designed to track the ethical sourcing of all construction materials, and the development of new research and assessment models for evaluating the environmental performance of the underground stations once they come into service.

238


The Tube has a total length of 402 km and its 11 lines and 270 stations are used by more than one billion passengers every year. One of the busiest and most important hubs is the station at Tottenham Court Road (TCR) in the heart of the city’s West End, used by more than 150 000 passengers daily – a figure that is soon expected to rise by one third when Crossrail services begin in 2018. The total number of passengers, also counting the Tube station, is expected to double. Here, a complete makeover is underway at a combined cost of more than GBP 1 billion (EUR 1.2 bn) to transform TCR into an ultra-modern subway terminal as well as a key interchange for the new Crossrail commuter trains that will eventually come in from the Dean Street side of the station. The new Crossrail station will be the length of three football fields with four stories going underground. The work on the subway upgrade at the TCR site includes: • Approximately 270 m of new tunnels • A new ticket hall (six times the size of the previous one) • New station entrances • Additional access points to the Northern and Central Line platforms • 8 new escalators and six elevators The contract for the TCR subway upgrade was awarded to the Taylor Woodrow/BAM Nuttall Joint Venture. Works include remodelling the existing station, reconstructing of the ticket hall and construction of the concrete box that will form the Crossrail Eastern Ticket Hall. The subway station will be enlarged to provide twice the capacity with new station entrances, modernization of the existing station passageways


Courtesy of London Underground /Crossrail

Artists impressions of the new, combined subway and Crossrail interchange at Tottenham Court Road, London.

and platforms, and a new concourse with a pedestrian link to the Crossrail station. For Taylor Woodrow/BAM Nuttall, the project has turned out to be a symbol of success, winning two major awards for outstanding achievement – Project of the Year from International Tunnelling Awards and The Infrastructure Award from The Institution of Civil Engineers (ICE). In a citation, the contractor was commended for making use of innovative designs that allowed the work to be carried out “to the highest standards of safety and quality and with no unplanned disruption to the operation of the station and railway.”

The TCR tunnels, which were completed in late 2013, are located some 25 m below the surface and vary in size from

All of the work had to be done while this busy station remained “live”, meaning that certain sections of the tunnels had to be installed while the station was in full operation and subway trains were running a few meters below or adjacent. Furthermore, as both civil and tunneling works were in progress side by side, there were difficult logistical challenges to be faced in terms of deliveries and mucking away. Delivery regulations in central London stipulated that trucks could only deliver and pick up at certain times of the day when noise and traffic were at a minimum.

Showcase for concrete spraying

Although much of the actual tunneling work is due to Taylor Woodrow/BAM Nuttall’s technical and managerial skills, a good portion of the credit is attributed to the application of state-of-the-art technology for sprayed concrete linings, provided by Atlas Copco MEYCO. An extensive product


239


The judges statement went on to point out: “This station is one of the busiest interchanges on the London Underground network and required the contractor to both plan the work and deliver it with exceptional skill. It is a very complex subterranean situation with many operational railway lines and station platforms to keep serviced and safe throughout construction. The scale of what has been achieved in such a confined location is an example to the industry for future urban underground construction projects.” (Source: International Tunnelling Awards)

3.5 –10 m in diameter. The longest tunnel was 110 m for a new Central Line Interchange Tunnel, while a 35 m long and 10 m diameter tunnel was constructed for the Northern Line concourse plus a number of cross passages that amounted to a further 65 m of tunnel.

BELOW THE STREETS OF LONDON: A SHOWCASE FOR SPRAYED CONCRETE

The MEYCO Oruga concrete spraying mobile in operation prior to the TCR project. The Oruga model is used in all types of wet or dry sprayed concrete applications, and is mounted on an agile carrier so that it can operate in the tightest possible tunnel profiles.

range for concrete spraying (shotcreting) met all of Taylor Woodrow/BAM Nuttall’s requirements for small, versatile and highly productive equipment that could operate in very confined spaces, particularly in the 3.5 m passenger tunnel walkways. In addition, the equipment had to be up and running 24 hours a day, so reliability and service support were paramount. MEYCO Suprema concrete spraying pumps, which are capable of spraying 14 m3 per hour theoretical at constant 75 bar, and MEYCO Oruga concrete spraying pumps were used to supply fiber-reinforced concrete coatings to the inside of the tunnel walls. This equipment was powered by compressed air supplied by two Atlas Copco GA 132FF stationary compressors, positioned on the surface. The GA 132FF is a singlestage, fully integrated rotary screw unit that delivers 7 bar of oil-free, dry air at the rate of 400 l/s. The air is introduced at the delivery nozzle to spray the concrete mix onto the receiving surface. Compared to dry mix, this so-called wet gun procedure produces less rebound and waste with the added advantage that larger volumes can be applied in a shorter time.

Working procedure

At the TCR project, the MEYCO teams usually consisted of three operatives: one for waterproofing and injecting, one to handle the concrete spraying equipment itself, and one to

240


liaise with the site contractor. On the larger tunnels, the teams began by concrete spraying the top heading after excavation, followed by the bench section and inverts. On the smaller tunnels, the whole tunnel was concrete sprayed in one go following excavation. The thickness of the layers varied between 150 mm and 500 mm and each layer took approximately 1 hour to cure, providing ground support and a safe working environment for the operatives. During peak periods, a workforce of some 300 were at work on the TCR site with many operating 8 hour shifts, round the clock. This meant four separate crews working throughout a 7 day week on a rota basis. David Harper, Project Manager, Major Projects for BAM Nuttall, comments: “There’s no doubt that the TCR project was somewhat of an iconic project for us in terms of logistics and environment management. It was a complex task in a confined space which meant that we had to change quite a lot of our working methods. “The concrete spraying part of the work was a key factor in meeting our targets. The MEYCO equipment worked very well, and apart from some occasional pump maintenance, we had virtually no issues with it at all. We are pleased that we were able to complete the concrete spraying part of the job on time and on budget, just as we’d planned.” Another contributing


factor was the smart use of pre-batched concrete stored in silos on site, which meant that there was very little waste. Harper says his company was also very satisfied with the service support provided by the Atlas Copco MEYCO team, but was quick to add that nothing was left to chance. The company doubled-up on everything, including all MEYCO equipment and emergency power generators in order to eliminate the risk of downtime. He concluded: “It was very important to us that the concrete spraying part of the job went according to plan. I am happy to say that it did, and going forward MEYCO would certainly be my first choice again.”

➊

At the time of writing, Taylor Woodrow/BAM Nuttall was already working on its next assignment – an upgrade of Victoria Station, another of London’s iconic mass transit interchanges and the company had already moved over its MEYCO gear to the new site to perform the required concrete spraying work.

➋

MEYCO equipment has also been selected by other contractors for upgrade works at eight other station sites: Farringdon Street, Hannover Square, Dean Street, Bond Street, Whitechapel, Finsbury Circus, Mile End, and the multijunction Eastern Running Tunnels. In all cases, MEYCO is able to select the most suitable units from its comprehensive range to suit the size and diameters of the underground structures.

➌

Future demands

It is already clear that the concrete spraying technology used at TCR and other stations will become increasingly in demand as Britain continues to modernize and expand its infrastructure, not only also because it is highly efficient, but because health and safety regulations now prohibit this type of work being done by hand. In the wake of the results achieved so far, MEYCO technology is well placed for a string of pending assignments. These include a new High Speed 2 (HS2) rail network that will dramatically reduce journey times from London to Birmingham; Crossrail 2, a potential new line linking North and South London; an extension to the Northern Line that will see the opening of two new stations by 2020, as well as upgrades of the Bank and Monument subway stations.

As many as eight MEYCO concrete spraying equipment were used at the Tottenham Court Road site for a range of different applications. These included MEYCO Piccola (1), MEYCO Oruga robots (2), MEYCO Suprema pumps (3) and MEYCO Potenza (4).


241


Looking further afield, projects such as the Glasgow Sewage Tunnel, the Hinkley Point Nuclear power station and the Coire Glas hydro scheme are also potential candidates for MEYCO concrete spraying technology. With tunneling work for the Crossrail part of the project due for completion at the end of 2014, the focus in 2015 and beyond will shift to station construction, fit-out and implementation of the railways. After this, there will be a lengthy period of testing and refinement before it becomes fully operational in 2018. ◙

➍

The long-awaited Second Avenue metro line, running from 125th Street to the Financial District, will ease overcrowding and congestion in New York.

Tough challenge

below the streets of Manhattan It has been described as the most complex subway project in the world in the heart of one of the most densely populated cities on the planet. New York’s long-awaited Second Avenue extension is making headway. New York’s long-awaited Second Avenue subway extension is now well underway on Manhattan’s East Side and will be a welcome addition to the city’s mass transit system. The first decision to build the new Second Avenue line on Manhattan’s East Side was taken as long ago as 1920 and since then the project has been repeatedly postponed. In

242


recent years however, renewed efforts to get the project back on track have succeeded. The new line under Second Avenue will ultimately be 8.5 km long, running from 125th Street in uptown Manhattan down to Hanover Square in the Financial District. Along the way, there will be three new stations – at 96th Street, 86th Street

SECOND AVENUE SUBWAY, NEW YORK, USA

Operations in full swing at 86th Street Station. Two Boomer E2 C face drilling rigs were carefully lowered down the shaft and into position.

and 72nd Street – plus branches linking to other sections of the city’s transport systems.

First phase on track

Among the many contractors engaged in the project are Skanska USA and Traylor Brothers who teamed up to excavate two construction shafts, North and South, and a rock cavern in between that will eventually house the new 86th Street station. For the drilling operations, the team used state-of-the-art equipment from Atlas Copco: two Boomer E2 C tunneling rigs, a Boomer T1 D, concrete spraying equipment from Atlas Copco MEYCO and a FlexiROC T30 R surface rig (formerly ROC D3).

Drilling the crown

The next step was to start drilling the crown of the cavern. However, there was not enough room to set up the Boomer E2 C rig at the right angle, and the Boomer T1 D was brought in to open up the shaft’s lower level and expose the top heading. The Boomer T1 D, which is usually used in narrow-vein mining applications, is compact and versatile. It has a carrier length of 5.5 m and a boom length of 4 m with the BMH 2825 feed system. It can also be used with the BUT 4 heavy duty boom system which provides a 900 mm extension and a 1 500 mm feed extension. Furthermore, the feed rollover is a full 360 degrees with a boom swing angle of ±30 degrees which allows good maneuverability. The rig was used to drill short cuts at 90 degrees into the shaft wall and


243


The work began with the sinking of a 10 m x 7 m shaft using the FlexiROC T30 R. Dust was a major challenge, but the contractors kept it well under control using blast mats and steel curtains to contain the flyrock and constant water spraying to dampen down the work areas.

Another challenge was to underpin the high-rise building on the east corner of Second Avenue and 83rd Street. As a part of this building is directly above the future portal to the 86th Street Station, it had to be underpinned before excavation of the construction and escalator shafts could begin.

NEW YORK'S SECOND AVENUE SUBWAY LINE GETS UNDERWAY

E. 125th St. E. 116th St. E. 106th St.

Central park

8 mft 26

18mft 5.5

FIRST PHASE

ANCILLARYTOP TOP HEADING HEADING ANCILLARY

E. 55th St.

INTERMEDIATEBENCH BENCH INTERMEDIATE

EXISTING TBM TUNNEL

E. 86th St.

E. 72nd St.

BOTTOM EXISTING BOTTOM BENCHTBM TUNNEL BENCH

M A N H AT TA N

5 mft 16

E. 96th St.

E. 42nd St. E. 34th St. E. 23rd St. E. 14th St.

E. Houston St. Grand St. Chatham Sq. Seaport station Hanover Sq.

Figure 1 (left): Cross section of the cavern construction for the new 86th Street Station showing the existing TBM (Tunnel Boring Machine) tunnels. Figure 2 (right): The Second Avenue subway will run from 125th Street to the Financial District.

it took several rounds before the area was big enough for the Boomer E2 C. In addition, the shaft floor had to be lowered by about 3 m and slightly angled to enable the boom to reach the cavern’s top heading. After blasting, the Boomer E2 C could finally be lowered down the shaft and into position. The crown of the cavern was located only 12 m below street level with an overhead rock cover of approximately 9 m. It will be 286 m long and has ancillary sections at each end, 74 m and 88 m long, with a so-called Public Cavern in between, 124 m long. The ancillary caverns were excavated by top heading, intermediate bench and bottom bench. The Public Cavern, being 3.6 m lower at the crown, was excavated as a top heading and bottom bench only. The top headings were split into a center pilot and two side slashes followed by the bench excavation. The top heading center pilots were 7.3 m high and the total width of the cavern is 21 m. One Boomer E2 C was operated from the North shaft and the other from the South shaft. Mucking was carried out by wheel loaders bringing the muck from the face to the shaft area followed by hoisting the muck in boxes up to street level.

244


Squeezing in the Boomer

The Boomer E2 C rigs were used to drill most of the blastholes in order to remove 140 000 m3 rock (108 000 m3 from the cavern with a further 32 000 m3 from the escalator tunnels and all other underground excavations) and was also used for drilling bolt holes. But calculating how much space was needed in the shaft to get the Boomer E2 C in place presented the biggest challenge. Kip McCalla, Atlas Copco Area Sales Manager at the time, says: “Having the dimensions of the rig and hole were not enough. We needed to know how the rig would react when articulating the booms in the shaft.” Joe Mela, Atlas Copco Area Salesman, was on site when the rig made its descent. “It was very, very tight and seemed like there was barely a coat of paint to spare,” he says. “The crew really showed their expertise in getting the rig into position.” Lars Jennemyr, Skanska Director of Underground Tunneling Operations, added: “We knew the Boomer would be able to drill within the area but making that happen was critical. By sending our crews to Atlas Copco’s Clarks Summit location,

SECOND AVENUE SUBWAY, NEW YORK, USA

th

th

k or W

m

fro

u So

Sh

aft

m

ro

kf

or W

r No

Sh

aft

8m

14

0m

15

rn

ve

i

bl

Pu

a cC

Figure 3: Skanska Traylor's assignment: The project involves two access shafts, a huge rock cavern between the shafts to eventually house the new 86th Streetsubway station, plus a range of auxiliary excavations.

they were able to practice the maneuver repeatedly with the Boomer to get the routine down.”

“I think the controls are smoother and the Rig Control System (RCS) makes it really easy to drill the pattern.”

Jennemyr continued: “When the booms travel up and down vertically, they spread wider from the center. By repeating this action and studying the booms’ movements, the crews were better able to understand what would happen in the shaft.”

The process for each drill pattern started with surveyor Paul Stogner. Skanska Superintendent John Kierman said: “Paul navigated the entire cavern. He would set up the transom and line up the first hole. It would go pretty fast from there.”

Once the Boomer E2 C was installed in the tunnel, face drilling advanced steadily and on schedule. The cavern advanced on three faces starting with the top heading and then the bench drilling. The center face of the top heading was drilled up to 7.3 m wide at the crown and 5.5 m to 6 m high on each side. Some 120 to 150 holes were drilled for the center and 70 to 90 holes for the sides. The tunnel face advanced 2.5–3.5 m with each round.

Drill operator Kevin Mari has worked on three projects in New York City using the Boomer E2 C. He said he appreciated the BUT 45 boom rotation device which allows ±190 degrees of rotation in both directions. Atlas Copco made a variety of consignment bits, steel and adapters available so that the crew had access to whatever they needed. The primary bit used was a 48 mm R32 flat face ballistic bit, although a range of sizes was available for the various drills and formation transitions.


245


The rock is competent Manhattan schist and granite with wide fracturing and is easily drilled. Typically, the drilling progressed at the rate of 3 m/min. Boomer operator Sean Keeffe has worked on several different Boomer models and said he especially liked the controls of the Boomer E2 C.

Stogner said the driller would line up the rig and set up on the first hole and then drill the pattern according to the computer’s direction, adding that it took about two minutes to set up and locate the first hole.

NEW YORK'S SECOND AVENUE SUBWAY LINE GETS UNDERWAY

The MEYCO factor

Rock stabilization was carried out with 6 m resin rock bolts above the springline. Working from the rigs’ service platforms, the bolts were placed in a 1.8 m x 3.5 m grid pattern and pre-stressed to 133.5 kN, installed below the springline. Concrete spraying was done in three phases using equipment from Atlas Copco MEYCO. Before bolting, the specifications called for a layer of steel fiber reinforced sprayed concrete with a minimum thickness of 50 mm. After bolting, a further layer of 100–150 mm was applied. Lastly, a smooth coating without fiber and with a minimum thickness of 25 mm was applied to cover the fibers before the PVC water membrane was installed. Gary Almeraris, Project Executive Manager, explained: “The key to concrete spraying is high quality, not high quantity of the mix. We used 400 bar steel fiber reinforced sprayed concrete with a superplasticizer.” An accelerator was added to give rapid support in just 10 hours and full support after 28 days. Every day, 60 – 90 m3 was sprayed using two Suprema concrete spraying pumps and two Potenza concrete spraying mobile units.

Steel fiber reinforced sprayed concrete was applied prior to bolting, using Atlas Copco MEYCO equipment.

The drill steel used was R32 × T38 hexagonal and round rod with a 57 mm coupler. Both were available in 3–4.8 m lengths with round rod in 5.5 and 6 m lengths. A shank adapter for the T38 was necessary for the COP 1838 rock drills used on both the Boomer E2 C drill rigs as well as the FlexiROC T30 R.

Round the clock schedule

The engineers worked round the clock, five days a week in three shifts – the first shift for drilling, charging and blasting, the second for mucking and scaling and the third for bolting, concrete spraying and initiating the next cycle. Tom O’Rourke, Skanska’s Project Manager said: “The same process was carried out with each slash: drill, blast, muck, bolt, sprayed concrete. For various reasons, the plan wasn’t always followed but we tried to keep it consistent. It was an intense five-day schedule. If we were drilling on one face, we’d be mucking on another and loading on the third.” The plan was originally set up to drill benches with horizontal blast holes, but once they tried benching vertically and succeeded, that’s the way the project continued. The benches were blasted in 4–5 m rounds, and the muck from the first bench dropped into the existing TBM (Tunnel Boring Machine) tunnels from where it was hoisted to the surface in connection with the excavation of the second bench.

246


Almeraris commented: “With the MEYCO we could spray 18 cubic meters an hour, with the guys in the cavern communicating with the guys on the surface by radio.” A tender on the Suprema concrete spraying pump unit on the surface controlled the ready-mix trucks so that the Suprema operators knew when the material was ready. “We applied sprayed concrete 80 to 100 mm at a time with a minimum of 175 mm overall. One layer could go on right after the other, and there was not really any waiting. The MEYCO concrete spraying equipment worked really well.” Throughout the project an Atlas Copco service technician was on site, day and night – Jim Mattila on the day shift and Scott Streichenwein on the night shift. Almeraris said: “The support we received from Atlas Copco was unbelievable. They were with us all along the way. Whenever we needed them, they were there – really part of the team.” The drilling and blasting on this section is complete, to be followed by the construction of the cast-in-situ concrete lining of invert, walls and arch concreting. Lastly, the escalator and adit tunnels will be completed. The project was due to be handed over to the city’s Metro Transit Authority at the end of 2014 for track laying, mechanical and electrical installations. This first phase of the new line, from 96th St. and 63rd St., is due to be opened in December 2016 and carry some 200 000 passengers per day. The entire project will cost a staggering USD 17 billion, but considering the relief it will bring – more than 4.3 million people ride the NY subway every day – most agree that it will be money well spent. ◙

NEW YORK SUBWAY, USA

247



This project is expected to meet the growth in demand for energy over the next 50–60 years, at least. Rafael Borgo, Commercial Director, CCC Ituango.

The dam construction area at the Ituango hydroelectric plant. The facility will be the largest of its kind in Colombia generating 2 400 MW, supplying around 17% of Colombia's demand for energy.

Harnessing the waters of Colombia

Ituango Hydroelectric Power Project, the largest hydropower plant in the country, is now under construction with advanced tunneling playing a crucial role in the process. When the Ituango hydroelectric power plant in the Antioquia region of Colombia comes on stream in 2020, it will add a further 2 400 MW to the national grid, enough to meet around 17% of the country’s energy needs. The very first feasibility study was conducted more than 30 years ago, but the plan had to be shelved for financial reasons. In 2010, however, the Antioquia administration, together with the multi-utility company EPM (Empresas Públicas de Medellín), enabled the project to finally go ahead.

248


They formed the Joint Venture EPM Ituango to finance, build and operate the project, estimated to cost USD 5.5 billion. Helping the contractors to meet their commitments is a large and diverse fleet of tunneling equipment and onsite service and maintenance, as well as constant supplies of rock drilling tools. Located in the northwestern region, Ituango is not only surrounded by high mountain scenery but also by high expectations.

ITUANGO, COLOMBIA

The Atlas Copco three-boom drill rig Boomer XE3 C, at work in the 240 m long powerhouse cavern where some 270 000 m3 of rock is to be excavated. It is one of seven Boomer rigs being used on the project.

“This project is a huge responsibility for everyone involved,” says Rafael Borgo, Commercial Director of CCC Ituango, the consortium in charge of the main phase of construction. “It is expected to provide enough energy to meet our growth in demand for at least the next 50 to 60 years.” Phase I consisted of preliminary construction work, including an access road to the site, a river diversion and an access tunnel to the underground area. The current phase comprises the main civil engineering works being handled by CCC Ituango, a consortium of contractors formed by Brazil’s Camargo Correa and Colombian firms Constructora Conconcreto and Coninsa Ramon H. The contract is valued at USD 1 billion. This group is not new to the world of energy, having worked together on the construction of Porce III, another EPM hydro project in the same area about 90 km northeast of Medellín.

Taming the Cauca River

The Ituango site is located between Toledo, Briceño and Ituango about 170 km north of Medellín, the capital of the Antioquia region. Here, in the area known as the Cauca Canyon, the 1 350 km long river flows between steep banks as it descends almost 800 m. The dam will be located about 8 km downstream from the Pescadero Bridge and immediately upstream from the discharge of the Ituango River into the Cauca River. At this spot, the waters have an average flow of 1 010 m3/s.


249

Hydroelectric power

“This is the second time we have worked together,” confirms Commercial Director Rafael Borgo. “The main advantage is not just that we know each other and the way we work, but also the confidence that we now have between the individual companies.”

He adds that Porce III, which started commercial operations in 2010, was completed on time. “We are expected to do the same here,” he says. “So to be able to meet this commitment in a project of this magnitude we need to work with reliable manufacturers, with machines we already know, and a company that can provide us with the after-sales service we need. That’s why we decided to use Atlas Copco.” Some 32 drill rigs, loaders, compressors, lighting towers and other auxiliary equipment from Atlas Copco are on site and two service contracts are in operation – one for service maintenance and parts supply, the other for rock drilling tools supply and bit grinding.

HARNESSING THE WATERS OF COLOMBIA

diversion of the Cauca River, which was achieved in February 2014 using two parallel horseshoe-shaped tunnels on the right bank of the river. These tunnels are 1 090 and 1 215 m long, 14 m in height and 14 m wide.

Dam, reservoir and powerhouse

The current phase includes construction of the dam, spillways, reservoir, power stations and all other related civil works. The 225 m high dam will be an ECRD type construction (earth and clay fill) featuring a 550 m long crest and a total volume of 20.1 million m 3. It will have a controlled, open-flow channel spillway with a discharge capacity of 22 600 m3/s. Featuring five radial gates and an intermediate discharge tunnel to control the filling of the reservoir, the spillway has a total length of 405 m, a width of 70–95 m and is built on a 12.5% slope. There will also be four cofferdams, two downstream and two upstream. The reservoir, which is 79 km long, will have a flood area of 3 800 ha and an active capacity of 980 million m3. Located underground and accessed by a 950 m long tunnel, the power station layout comprises four caverns: the main powerhouse, a transformer cavern upstream and two surge chambers downstream (see Figure 1). Figure 1: The underground layout at Ituango: 1. Powerhouse cavern 2. Transformer cavern 3. No.1 downstream surge tank 4. No.2 downstream surge tank.

The project area is accessed via two main roadways, including the 38 km road that was created during the preliminary construction work. This runs along the left bank of the Cauca River, and building it was no easy task. “The mountainous topography is a big challenge as it makes access very complicated,” explains Rogerio Beloni, CCC Ituango Maintenance Director. “Although some roads are now paved, they are very narrow and have lots of bends. To make them wider would be a huge task and very costly.” It was difficult to transport some of the largest pieces of equipment to the site, and some items had to be taken apart and then re-assembled in-situ. Another road is also being built from Valdivia Port to Ituango in order to transport big items such as the turbines and generators that will start arriving when the project is finished and enters its third phase.

Varying ground

The ground is generally a mixture of rock and soil and the conditions at each worksite are classified on a scale of 1 to 5, where 1 is the optimum and 5 is poor. Beloni says: “There are areas that are not very stable, especially in the inclines, which can be prone to landslides in the winter months. Although they’re not major ones, we have to take this into account in our planning.” Some geological faults have been found underground in some of the caverns, which can make excavation difficult. An important step in the project was the temporary

250


The main powerhouse cavern is 240 m long, 23 m wide 49 m high, representing an excavation of approximately 270 000 m3. It will house eight Francis-type turbines of 300 MW each. It will also house eight vertical axis synchronic generators, electromechanical auxiliary equipment, control center and office facilities. The turbines and generators are divided into two groups of four. The generators will be fed by eight headrace tunnels that have a design flow of 168.8 m 3/s, with sluice gates in vertical shafts. After passing through the turbines, the water will flow to the two downstream surge caverns. The water will then be discharged into the Cauca River via four tailrace tunnels, two from each surge tank.

The drill fleet

The Atlas Copco drill rig fleet includes seven Boomer rigs of various models with one, two or three booms; 15 FlexiROC T35 drill rigs; four Diamec 262 (now Diamec U6) core drilling rigs; three Scooptram ST2G loaders; four GA 132 and two GA 160 electric compressors; four XAS 375 JD and two XAS 750 JD diesel compressors; and a number of QLT M10 lighting towers. Atlas Copco also provides training for the drill rig operators to complement the contractors’ own training programs. Beloni says: “We have people here who worked in Porce III and have experience with some of the equipment, but we also have people without experience at all who are being trained here. This way they learn at work and acquire a new skill.” The Boomer rigs (Boomer XE3 C, XL3 D, E2 C, L2 C, L2 D, S1 D and T1 D) are all working underground. “I’ve been

ITUANGO, COLOMBIA

FlexiROC T35 drill rigs working on the excavation of the spillway area, drilling blastholes, boltholes and holes for drainage.

drilling all over the caverns with this machine,” says Luis Alfonso Rodriguez, operator of a Boomer XE3 C. A local from the Antioquia region, Rodriguez has seven years of experience as an operator, some of which he gained at Porce III. There he experienced the Rig Control System (RCS), which allows several levels of automation – Basic, Regular and Total. The rigs on the site are all equipped for the fully automated ABC Total level (Advanced Boom Control). “It was easy to understand and to explain to the trainee operator; he got it straightaway,” says Rodriquez, referring to Jorge Andres Flores, the trainee now under his wing. The rig is used to drill 4 m blastholes with 51 mm drill bits and, according to Rodriguez, takes about one hour to drill and blast one round because the rock conditions at the site are Type 4 (quite poor). “This is a great, powerful machine, better than the previous one I worked with,” he says. “What I like the most is the visibility from the cabin so I can really see what I’m doing.”

The FlexiROC T35 (formerly ROC D7) tophammer surface drill rigs are designed for high performance in demanding construction applications. “In the surface area we are excavating about 12 000 m3 of rock per day in two 12-hour shifts,” says Jose Paulo Fernandes, CCC Ituango’s Production Coordinator, Surface. Of the 15 FlexiROC rigs, 12 are working on the excavation of the spillway area drilling blastholes, bolt holes and holes for drainage, and two are working underground while one is on standby. “Right now I’m drilling 9 m bolt holes and can install 30 to 40 bolts in one shift,” says Mariano de Jesus Gomez Atehortua, one of the operators working in the spillway area. Due to the mixed quality of the rock he says it takes him about 20 minutes per bolt.

Controlled excavation

Fernandes confirms that the project is on track. “We had planned to excavate a total of 336 000 m3 during March and that’s what we achieved,” he says. Two FlexiROC rigs are working in the caverns. “We do between 1 500 and 1 700 m3 per day,” Fernandes continues. “Blasting underground is also easier as we don’t have any interference like in surface drilling where we have to cordon off an area and wait for it to be clear.” The four Diamec rigs in the fleet are used for geological investigations. These compact rigs make them ideal


251

Hydroelectric power

A variety of support methods are employed, including steel arches, sprayed concrete, mesh and rock bolting, and some of the Boomer rigs are being used for the installation of 12 m long resin rock bolts. Mario Restrepo, CCC Ituango’s Underground Excavation Manager, comments: “I can say that these efficient machines are at the forefront of underground drilling technology.”

Full on for FlexiROC

HARNESSING THE WATERS OF COLOMBIA

The onsite grinding center at Ituango is used to re-grind approximately 600 drill bits per day.

for underground core drilling, and the modularized system of rig, power unit, flushing pumps and control panel means they can be used both on the surface and underground. “They’re good machines,” says Beloni. “We’ve already used them inside the caverns and outside in the spillway area, and right now they’re working in the adduction channel above the spillway.” Along with the drill rigs, Atlas Copco compressors and lighting towers help to keep the operations running smoothly. The QLT H40 lighting towers feature a metallic enclosure with an electrical cubicle for control and protection; a hydraulically raised mast that extends vertically up to 9.2 m in 15 seconds and rotates 350 degrees, stabilization legs and brakes. The towers and diesel compressors have been used prior to the installation of fixed electrical power.

technicians in Medellín or Bogota. Cruz’s team at Ituango includes 13 service technicians plus support staff. In each of the two shifts at the project, six technicians are always on site where they have offices, containers for storage of key spare parts and one workshop for rig maintenance. Cruz points out: “Our job is to provide a speedy and effective maintenance service for any need that comes up during the construction of this challenging project.”

Rock tools and grinding

Discussing the maintenance and parts contracts, Darwin Cruz, Atlas Copco Service Agreement Manager, says: “ We provide constant onsite technical support, with both preventative and corrective maintenance service, and help with the sourcing and installation of original parts when required.”

Atlas Copco supplies all the drill steel for the entire equipment fleet, as well as a grinding service for all of the rock drilling tools. The drill steel team is headed up by Damian Saldarriaga, Drilling Tools Supply and Grinding Manager. There are four containers on site, one used as an office, two for storage of rock tools and another as a grinding center. There are two grinding technicians, one per shift, using Secoroc’s Grind Matic BQ3, a machine specially designed for threaded and tapered bits with spherical and ballistic buttons. Grinding goes hand in hand with production both on the surface and underground, says Saldarriaga. “Every day we grind about 600 bits. We also have small, portable grinding machines available as backup. Our job is to guarantee the continuity of the service at all costs.”

For the maintenance of the rest of the fleet, such as compressors and lighting towers, the site is supported by Atlas Copco

Each rock drilling tool delivered is identified according to a specific code that helps to follow the performance of each

Maintenance and technical support

252


ITUANGO, COLOMBIA

individual tool. Explains Saldarriaga: “If a machine is reaching low productivity levels, we go to the field, inspect it and analyze what factors are influencing the lifespan of the tool. We can then give accurate feedback to our client about meters drilled and the reason for replacement. The final objective is to help improve the client’s productivity so that they get the lowest cost per meter drilled.”

Service and interaction

Monitoring the performance of each tool is possible due to special software developed in Colombia and used at Porce III. This was later improved and developed into a cost-per-drilledmeter contract in the first phase at Ituango. “The results were good, so we developed this newer version to achieve better service for the client,” says Julio Cobos, Atlas Copco Product Manager for rock drilling tools. “For us it is a matter of reliability,” concludes Beloni. “We work with other brands too, but we always try to work with a reliable manufacturer. Atlas Copco is a well-known brand, has reliable equipment and good after-sales support, and that is very, very important for us.”

Social impact

There’s no denying that a project of this magnitude will impact the local area, bringing about economic and social change. The intention is for this to be more positive than negative. For example, due the remoteness of the area and difficult terrain, it would take nearly nine hours to get to Ituango from Medellín, the nearest large city. Now it is possible to do so in four to five hours. In addition, with more people working in the area, including some military presence, the area is considered to be safer. CCC Ituango has agreed to employ mostly local people, and at the time of writing, the workforce numbered around 3 900. Rafael Borgo, Commercial Director, says: “Once they start working, training and acquiring skills, they’ve got the opportunity to change the quality of their lives for the better. Here they’ll acquire skills and experience that will serve them well in the future.” In connection with the project, the consortium has launched an education initiative both internally and externally. Internally, it provides basic education for workers, helping them to improve reading and writing skills or complete their next level of formal education.

Top (center left and right): Rogerio Beloni, Maintenance Director and Rafael Borgio, Commercial Director of CCC Ituango with representatives from Atlas Copco. Bottom: One of 13 service technicians on site, working two shifts to keep operations running smoothly.


253

Hydroelectric power

“This is a very rewarding experience,” says Borga. Also, the extra coaching helps them to work with advanced, computerized machines.” Externally, the company supports local schools, and once a year, company personnel including managers, spend a day as volunteers working with social issues in the local community. ◙

In the end, it's all up to the rock and the driller's efficiency. Jostein Veåsen, Project Manager, Veidekke Entreprenør

Boomer face drilling rigs were used to develop a total of 19.6 km of tunnels diverting water to two separate hydropower stations in south-central Norway.

Water transfer for Norwegian hydros

Norway has boosted its hydroelectric capacity by harnessing more water from its mountain streams. This involves upgrading of existing hydropower facilities with new tunnels being driven for increased “water control”. Norwegian tunneling engineers have been hard at work over the past few years diverting water from a complex system of mountain streams to boost the power output of two hydropower plants in the south-central part of the country. The project was carried out as two separate developments known as Brokke Nord (North) and Brokke Sør (South) and involved the construction of a 19.6 km system of water transfer tunnels. These tunnels were used to boost the volume of water flowing into the plants, increasing their capacity by some

254


24 MW and giving the facility a total output of 175 GWh per year. Described as a water control system, the Brokke North (11.7 km) and Brokke South (7.9 km) projects are together diverting the flows from seven small rivers into tunnels and natural watercourses. A total volume of 347 000 m3 of rock has been excavated for both projects. The project was carried out by the Norwegian power company Otra Kraft, which, following the Brokke North/South development, generates around 2 525 GWh of power per year.

BROKKE NORTH AND SOUTH, NORWAY

This amounts to approximately 2.2% of Norway’s national electrical power production. The whole project, which started in April 2012, was supervised by the Norwegian national power generation organization Statkraft and came on stream in the spring of 2014.

SKARG Bykle

BROKKE NORD

Brokke North

The Brokke North part of the scheme was located in the mountains midway between the cities of Stavanger and Oslo. This was the larger of the two sites, and in addition to the water transfer tunnel system, it also included the construction of a dam wall 50 m high and 150 m wide.

Rygnestad

This dam, at Sarvsfoss near the town of Bykle, was used to create a small reservoir to collect additional water supplies and add to the flow from the Otra River, which feeds the recently built Skarg power plant near Botsvatn. The Skarg plant houses two turbines to generate 69 GWh per year – enough to serve about 3 500 individual homes. The Brokke Nord contract, totaling 500 M NOK (65.5 M EUR), was won by Implenia Norge, a subsidiary of the Swiss-based international construction contractor Implenia, and had a team of 120 working on the tunneling and an additional 80 people on other construction.

Valle Otra

A tunnel, driven with three headings, was constructed to collect water between the main intake at Bjørnarå and Stemtjørnbekken and deliver it to the Sarvsfoss reservoir. There are also intermediate intakes at Blautgrjotbekken, Løyningsbekken, Optestøylbekken and Bjorbekken. The main tunneling construction site was located between Blautgrjotbekken and the Løyningsbekken intake, high above the main RV9 road. From there, a twin-heading tunnel runs for 3 km, to Bjørnarå in one direction and, via the main south portal, to Bjorbekken in the other direction. There is an additional 600 m of tunnel that diverts the increased water flow from the Sarvsfoss reservoir. The extension is connected to an existing 4.5 km tunnel driven in 1976 and runs between Lauvtjønn and the new Skarg power station.

Brokke

BROKKE

Hylestad

BROKKE SØR

All of the tunnels have a cross section of 20–22 m3, a height of 5.5 m and a width of 4.5 m. For the drilling, Implenia used two new Boomer E2 C drill rigs and one older L2 C twinboom drill rig, all from Atlas Copco. Power station New tunnels Existing tunnels

HEKNI

Figure 1: The Brokke North and South projects involved the excavation of 347 000 m 3 of rock. Seven rivers and watercourses are diverted in order to generate a total 175 GW per year.


255

Hydroelectric power

The older drill rig and one of the two Boomer E2 C rigs were deployed from the Blautgrjotbekken access tunnel at Bjørnarå to drive the two faces from there to Bjørnarå, as well as a a curved drive for the main run north towards the Sarvsfoss reservoir. The other Boomer E2 C drill rig worked its way from Stemtjørnbekken southwards to meet the other Boomer E2 C face. A standard drilling pattern of 73 holes was used consisting of nine holes in a burn cut in the lower central

IN THE MOUNTAINS OF NORWAY: NEW TUNNELS FOR WATER TRANSFER

Ventilation was provided at the Brokke South worksite using an Atlas Copco ventilation system equipped with two- and three-stage 900 mm fans, adapted to the 7.13 km of tunnels being driven. (Note: The ventilation system from Atlas Copco is now named Serpent Ventilation System.)

position. The drilling pattern was installed in the rigs’ RCS (Rig Control System). Besides the advanced RCS, the Boomer E2 C was equipped with COP 3038 hydraulic rock drills and heavy duty, squaresection BUT 45 booms. The rock drills featured pressurized housings and mated surfaces to minimize internal contamination. The combination of RCS together with the BUT 45 booms provided fast and accurate positioning between blasthole collaring, taking around 50% less time than conventional rigs. The double rotation unit provided ±190 degree feed rollover and ±135 degree feed rotation. Standard functions of the RCS include soft collaring and the anti-jamming function of the Rotation Pressure Control Feed (RPCF). The rigs’ integrated diagnostic and event-logging system provided the basis for efficient maintenance. Atlas Copco also provided service support with on-site, containerized mobile workshops, with the workshop at the Bjørnarå site also equipped with Atlas Copco Secoroc’s Grind Matic BQ3 button bit grinder for drill bit grinding. Boomer E2 C operator Kjetil Holte, who has more than 15 years of blasthole drilling experience, said he was happy with the comfort and ease of operation of the Boomer E2 C compared with earlier models he has operated. Load-hauldump vehicles with 14 t capacity handled the mucking out and transfer of the excavated material to trucks for removal

256


from the tunnels to the disposal site. One special excavation operation focused on the removal of 15 000 m3 of material from the foundations of the Skarg dam construction site. This material, which was mainly gravel to be used for concrete aggregate, was being removed via the lower tunnel as there was no other practical route out of the site. For most support requirements, a layer of fiber-reinforced sprayed concrete was sufficient, including roof rock-bolt holes drilled using the same Atlas Copco drill rig that was used for blasthole drilling.

Brokke South

Although the Brokke Nord and Brokke South projects are linked strategically and financially, the only physical link between them is the water transmission tunnel network.The Brokke South contract, valued at NOK166 M (EUR 21.28 M), was won by Veidekke Entreprenør, the largest Norwegian-owned contractor with an annual turnover of SKR 17.9 billion and 6 100 employees. The company specializes in tunneling but also engages in the construction of dams and power plants both at home and abroad. For Brokke South, Veidekke also chose to rely on Atlas Copco Boomer face drilling rigs. The main aim of this project was to collect water from three inlets in the hills to the southwest of the Otra river valley, deliver it through 7.13 km of tunnels to an existing water


tunnel, and then on to the Brokke power station. As a result, the capacity of the station has been increased to 102 GWh, with a further 4 GWh added to the capacity of a smaller power station named Hekni further downstream. The Brokke station was built in 1964, and the upgrade has increased the water catchment area for the station by a further 50 km 2. At Farå near the community of Brokke Hyttegrend, a small dam and cross-valley pipeline has been constructed to accommodate the new flow. An initial tunnel of 750 m had to be driven from the Lisle Myklevatn Lake up to the highest intake at Strendetjørnbekken. Lisle Myklevatn is also the head intake of the main tunnel where Veidekke has built a small dam wall measuring 30 m wide and 5 m high. The main construction site was at Fjellskarå, up a steep winding track from the township of Rysstad. From here, two tunnels, one up to Lisle Myklevatn and the other to the valley at Farå, were driven to complete the main tunnel where, via a cross-valley pipeline, water joins the existing feed tunnel to the Brokke power station. Fjellskarå is also the location of another water intake to the tunnel. All intakes are formed as 5 m deep shafts to the water transmission tunnel. The small valley at Fjellskarå was also a convenient place to dispose of the excavated material by levelling up hollows rather than trucking it out along a difficult access route. The 3 km south main drive from Fjellskarå to Lisle Myklevatn was at an up-gradient of 1:200. The 4.1 km long north drive to Farå was at a 1:400 up-gradient, while the short drive from Myklevatn to Strendetjørnbekken was at an up-gradient of 1:150. All of the main tunnels are horseshoe-shaped and quite narrow, 3.5 m wide and 4.5 m in height, and have a cross section of 14 m3, while the 150 m long access tunnel at Fjellskarå has a cross section of 16 m2. Veidekke operated two Atlas Copco Boomer rigs equipped with service platforms. At first, these were a Boomer M2 C and an older Boomer L2 C. Another Boomer M2 C equipped with a BUT 32 boom and a COP 2238 rock drill was later added to the fleet. With its two BUT 32 heavy duty booms, the Boomer M2 C has a face coverage area of 65 m2. It was equipped with dualdampened COP 2238 22kW hydraulic drills for high-speed drilling in the hole diameter range of 38-64 mm.

The Atlas Copco supply package also included drill steel, bits and other consumables, and a drill steel container and

Implenia's mobile workshop at the Brokke North tunneling site.


257

Hydroelectric power

These drills featured pressurized housing and mating surfaces to deter internal contamination. The booms feature double-tripod suspension for accurate hydraulic parallel holding in all directions. The Boomer L2 C rig has a larger face coverage of up to 104 m 2 but has COP 1838HD drills rated at 18 kW delivered at impact. The hole diameter range is 38–64 mm.

IN THE MOUNTAINS OF NORWAY: NEW TUNNELS FOR WATER TRANSFER

created at the site office using the Underground Manager software which is an option that is available with ABC Regular. As all main drives were of the same design, a standard drill pattern of 55 holes was used, with four larger diameter holes in a burn cut in the center. In addition to the standard tunneling dimensions, Veidekke excavated a 20 m long loading bay area as a “slash,” cut at a spacing interval of 120 m along the tunnel drive. These bypasses made equipment travel more efficient and increased the total width at these points to 7 m. Veidekke’s Project Manager, Jostein Veåsen, was satisfied with the performance of the Boomer rigs: “It was as I expected and it all worked out fine. There are some small differences between the M2 C and L2 C on reach, boom positioning and drilling speed, but in the end it’s all up to the rock and the driller’s efficiency.” The face was charged with post-sensitized bulk explosive from Orica and initiated with Nonel non-electric detonation. An average of 6–7 blasts were carried out per day on the two faces. Each blast achieved a “pull” of 4.2–4.4 m resulting in 120–140 m3 plus “swell.” Loading out one blast took approximately three hours. This was accomplished with narrow profile wheel loaders with a central loader conveyor and a rented fleet of four specialist dumper trucks of 10 m3 capacity, requiring about 12 loads per blast. The plant fleet also included a rough terrain access platform for work on the service lines and ventilation equipment.

The Secoroc Grind Matic BQ3 button bit grinder keeps drill bits at top condition at the Brokke South onsite workshop.

workshop with a Secoroc Grind Matic BQ3 button bit grinder to ensure that the drilling equipment was kept in top condition throughout the excavation process. The Boomer rigs were operated in the ABC Regular (Advanced Boom Control) mode with guidance based on a laser beam referenced 500–700 m from the face. The correct rig position was checked after each blast and a tell-tale device warned of any disturbance to the laser source. ABC Regular offers semi-automatic drilling functions. With the help of predetermined drill plans that are transferred to the rig´s operating system, the operator can position and direct the feed for precise drilling results. Drill plans are

258


Ventilation was provided by Atlas Copco fans, 900 mm in diameter and sited at the portals. The longest drive required airflow at the capacity limit for a standard fan, so three-stage fans were utilized to give the additional developed pressure capacity for the longer drive. Two-stage fans were used for the drive to Lisle Mylevatn. Project Manager Veåsen also reported that the excavated ground had been quite solid, hard and competent rock composed of the usual mixture of granites and gneiss often found in Norway. This meant that support requirements were limited. The standard rock bolts used were secured with polyester resin cartridges, with an extra four rock bolts used in the loading bay excavations, each 2.4 m long. Grout injection for ground consolidation was only required at the junction of the Fjellskarå access tunnel and the main water tunnel drives. Veidekke achieved its first breakthrough on the main tunneling drives two months ahead of schedule. This represented an overall progress rate of 65 m per week. The tunneling team worked on two 10-hour shifts for a six-day week, with the workforce split into three crews of eight tunnelers each. ◙


259

Hydroelectric power


The excavation of the Govddesåga hydropower plant is going full steam ahead thanks to Atlas Copco Häggloader and its continuous loading system. Here, a helicopter is used to transport concrete to the intake level worksite at 546 m asl.

Continuous loading in Fjord country

Haulage logistics can be challenging in the construction of small tunnels in mountainous terrain. Excavation work for the Govddesåga hydropower station in Norway is going full steam ahead thanks to the Häggloader – an efficient system for continuous loading. The technique of running water through turbines to generate renewable energy has long been practiced and refined in Norway, the Scandinavian country where hydropower accounts for no less than 99% of the domestic electricity supply. This impressive achievement results in approximately 120 TWh of electric power in a year with normal precipitation and is also what makes Norway the largest hydropower producer in Europe – and the sixth largest producer in the world. With many rivers and streams tucked into the stunning landscape of fjords and Alpine-like mountains, Norway’s topography has proven to be highly favorable for renewable

260


hydroelectricity. A large number of facilities were established by the Norwegian government during the second half of the 20 th century, and many of these continue to be run by the state-owned power company Statkraft. Today, private initiative is increasingly paving the way for new, smaller-sized hydropower plants. These are being designed to boost Norway’s hydro output in order to create a green energy surplus that is expected to open up a large export market. At least 15 new hydropower plants will be introduced in the country before 2020, and a further three

GOVDDESÅGA, NORWAY

facilities are in the planning stages. Among the projects where construction is well underway is the Govddesåga Power Station (Govddesåga Kraftvek AS) in the Nordland region of Norway, which extends into the Arctic Circle. Here, tunneling engineers from local contractor Fauskebygg AS are using the drill and blast method to excavate key underground HPP elements – powerhouse, headrace, tailrace, access and haulage tunnels. The hydro project, which is named after a nearby stream, is located in the Salten mountain range in the municipality of Beiarn, some 115 km southeast of the coastal town Bodø, which is a starting point for many Arctic expeditions. To facilitate a more efficient and predictable production cycle at the Govddesåga worksite, tailored to the 20.5 m 2 cross section of the hydro tunnel drives, Fauskebygg has introduced a continuous loading system for its haulage operations at the headrace tunnel using the Atlas Copco Häggloader 10HR-B.

Tapping the force of Govddesåga

The development of hydropower plants is not a new occurrence for the inhabitants of Beiarn and its mountainous surroundings. In fact, the Govddesåga hydropower station will be developed using an existing dam, Arstaddalsmagasinet, which was constructed in 1961. The dam is already used to partly regulate the water for another neighboring hydro facility in Sundsfjord. Govddesåga will have an installed capacity of 25 MW when it comes online in 2017. Its three Francis turbines will by then process 13.7 m3 of water per second, which is diverted from the Govddesåga stream at the 546 m asl intake level. Here, an intake pond is being constructed that will lead the water to the inlet tunnel. The small reservoir is designed for a holding capacity of 110 000 m2, which corresponds to approximately half a day’s power production. As soon as the project was approved by Norway’s Water Resourcces and Energy Directorate, the first phase of excavation went ahead. Some 3.4 km of tunnels are to be driven in total, of which the headrace tunnel is the longest, as well as an underground powerhouse, 32 x 13.5 m in size. The plant will not feature a penstock as the headrace tunnel will take full advantage of a steep 226 m elevation drop to the powerhouse. The water from Govddesåga will exit via a tailrace tunnel, located at 333 m asl, in the Arstaddal Dam area where an old stone quarry is also located and no longer in operation.

months, the snow-free period, which accounts for approximately 50 of the 58 GWh of annual energy production. The power production is equivalent to the annual consumption of roughly 2 900 households. The Govddesåga project is being developed by SKS Produksjon AS, a subsidiary of Salten Kraftsamband (SKS) and the second largest power producer in the Nordland region after Statskraft, and will be co-owned together with Statskog SF and Clemens Kraft AS.

Tunneling progress

For the most part, ground conditions have been favorable, and the need for rock reinforcement has been minimal during the drill and blast excavation, with an average of seven bolts installed per blasted round. However, critical zones characterized by heavy layers of slate have been encountered along the headrace tunnel. These have been planned for using data provided by geologists studying the site. “Just now we are approaching a difficult section extending for about 10 meters with heavy rock characteristics. It makes drilling a little more challenging as cuttings tend to get stuck,” says John Magne Hansen, Shift Manager at contractor Fauskebygg, whose team is making steady progress on the 2.4 km long headrace tunnel.


261

Hydroelectric power

Thanks to the favorable conditions and the possibility of using an existing dam, the Govddesåga hydro plant is being constructed with minimized impact on surrounding nature and vegetation. Having said this, the water f low in the Govddesåga stream needs to be kept at acceptable levels, and for this reason, a maximum limit has been set for the volume of water that is diverted. Approximately 90% of the facility’s yearly power production will be generated during the summer

The Atlas Copco Häggloader is an electrically powered, continuous loading system that is ideally suited to small and medium-sized tunnels. It improves the working environment and reduces running costs, ventilation costs and costs for excavating loading bays.

CONTINUOUS LOADING AT GOVDDESÅGA

“We have come about halfway in terms of the volume of rock to be excavated for the project. Overall, things are progressing very well,” he says. The access tunnel at the Arstaddal Dam is accessed by road from Beiarn, which is situated about 25 km from the worksite. The intake level, by contrast, cannot be accessed by road and, for this reason, a helicopter is used to transport engineers, equipment and material from the dam area, including a continuous supply of concrete used for developing the 30 m long diversion reservoir. Fauskebygg’s drilling fleet includes an Atlas Copco Boomer M2 C and a Boomer E2 C equipped with COP 2238 drills. The blastholes are 4.6 m long and 56 holes are drilled per round. Each round is blasted using emulsion explosives and involves haulage of roughly 175 m3 of waste rock, which is deposited in the old stone quarry area. The equipment is being used on two fronts, the headrace tunnel and the powerhouse, the latter of which is being excavated by drilling and blasting horizontal benches. The construction work is divided into two eight-hour shifts with three operators for each team. Fauskebygg has a crew of two for drilling and one operator for mucking out using a new equipment unit in the company’s fleet – the Atlas Copco Häggloader 10HR-B.

Continuous loading: a suitable option

Due to the relatively small dimensions of the tunnels to be excavated, measuring 4.5 m wide x 5 m high and featuring a wedge at the roof of the tunnel profile to provide space for ventilation ducts, Fauskebygg made the decision to try an alternative approach for its loading operations. And the investment has paid off. “In small tunnels such as these, logistics are tricky because a larger number of loading bays need to be excavated to enable the efficient flow of haulage vehicles,” explains John Magne Hansen. “The Häggloader saved us the effort of having to excavate 50 cubic meters of rock for every niche, and we would have needed about 10 niches.” Solving the haulage logistics was a key challenge for Fauskebygg, particularly for the 2.4 km long headrace tunnel, which is the longest on the project. The company wanted to avoid having haulage equipment standing idle, waiting to access the muck pile. “In our planning, we could see that the longer the tunnel would get, the greater the logistics problem would become. By introducing the Häggloader, we reduced the required number of niches to four and also managed to maintain a consistent two-hour cycle time for mucking out and transport.” Top: Service Manager Svein Ruddås. Center: The Häggloader working on a two-hour cycle for mucking out and transport. Bottom: The Hägg-loader's conveyor carries the blasted material up and over to a waiting truck.

262


The aim of minimizing the volume of excavated rock was also important due to a limited capacity for depositing rock at the

GOVDDESÅGA, NORWAY

Using dual digging arms or a backhoe bucket, as shown here, the Häggloader moves blasted rock onto a conveyor at a continuous pace. The conveyor is matched with haulage trucks.

old stone quarry, which is located near the dam. John Magne Hansen continues: “Beyond this, we were very pleased to get electrically powered loading into our operations as it has benefited the working environment and reduced costs.”

The Häggloader concept

Based on the principle of continuous loading, the Häggloader rig comes in four different models, wheel, rail and crawlermounted, and is ideally suited to small and medium-sized tunnels. The Häggloader is equipped with dual digging arms, or an optional backhoe digging system, dozer blades and a conveyor, and is designed for tunnel cross sections starting from 8 m2 and upwards. In the case of all models, blasted rock is mechanically shoveled from the muck pile onto the Häggloader’s conveyor. The material is then transported up and over the rig, creating a continuous flow of rock to the haulage truck. The Häggloader conveyor is easily matched with a range of different trucks and dump buckets.

Apart from enabling tunneling engineers to choose between dual digging arms and a single bucket backhoe, the Häggloader system is also flexible for different tunneling environments because it can be powered by either a 74kW electric engine or, if needed, by diesel. This means that fuel consumption and ventilation costs can be significantly reduced. Using diesel as a secondary power source may be useful if there is a problem with the electricity supply or when tramming longer distances as the speed capacity is greater. Beyond this, there is little reason to switch from electric power, which also keeps the temperature at the tunnel face at lower levels to make the working environment more agreeable for the operator. Once the Häggloader 10HR-B arrived on site, the tunneling team from Fauskebygg began to explore some undeniable benefits of the new continuous loader.

Improved environment

In the case of a traditional haulage setup using LHDs, the vehicles are in constant motion at the worksite. This means that operators need to keep a close eye on all vehicles and their movements because the risk of hazard is greater.


263

Hydroelectric power

Not only does the Häggloader reduce the number of loading bays, which helps to minimize the overall project time, it also has a stationary position while in operation. This will enable significant cost cuts in terms of fewer tire changes and reduced wear and tear on roads. Fauskebygg has chosen to employ the largest model, the rubber-wheeled Häggloader 10HR-B featuring a loading capacity of up to 4.5 loose m 3/min.

Although it is the largest model in the range, it has a compact design and is optimized for narrow tunnels and tight cornering thanks to four-wheel steering.

CONTINUOUS LOADING AT GOVDDESÅGA

Tunneling solution in the fjords: Continuous loading with the Atlas Copco Häggloader has solved a number of challenges for Norwegian contractor Fauskebygg AS. Loader operator Lars Lunde (center) with Boomer operator Ronny Bakk (left) and Shift Manager John Magne Hansen (right).

By contrast, the Häggloader has a stationary position, meaning that the operator can completely focus on the task of loading and making sure that blasted materials move onto the conveyor at a continuous pace. “You don’t have to twist and turn your body to feel safe and in control while working,” says Lars Lunde, Fauskebygg’s Häggloader operator. “The fact that we can use electrical power improves the air quality and keeps temperatures within tolerable limits.” He describes an incident when a power cable mounted on the wall of the tunnel was damaged by a moving truck. While the cable was being fixed, the team switched the Häggloader to diesel power and, as a result, the temperature at the tunnel face quickly reached 40 degrees Celsius. “I was relieved to switch back to electric power.” The FOPS II approved cabin has an ergonomic driver’s seat with armrest-mounted joysticks. It is equipped with an air conditioner, heater, protection bars, LCD technology for performance data, as well as two rear-mounted cameras for maximum visibility. The cameras are useful to monitor the conveyor and haulage truck behind the rig. Lunde took part in a Häggloader training course provided by Atlas Copco

264


and says that it took him about two weeks to achieve a good level of proficiency using the new continuous loader. On previous tunneling projects, Fauskebygg has used Atlas Copco Scooptram ST1030 LHD with side-dumping buckets, but in these cases, the tunnels had a cross section of at least 36 m 2. This meant that conventional loading was a viable option. The job of removing loose rock after blasting, however, has reportedly become easier with the Häggloader system. “This is why we chose the Häggloader 10HR-B model because we get a two-in-one function. We can use it for loading but also for scaling and to clear the ditches,” says John Magne Hansen, Shift Manager.

Oversized boulders

The critical zones along the headrace tunnel line are marked as blue sections on the construction plan in the Govddesåga site office. When these zones are approached, the team from Fauskebygg knows how to prepare, not just in terms of drilling but also loading. In the critical sections, oversized boulders are sometimes found in the muck pile as a result of blasting the challenging layers of slate. If the boulders are 1 x 1.5 m in diameter or more, they may be too large for the Häggloader conveyor – but the team has a fast, easy solution.

GOVDDESÅGA, NORWAY

The boulders, explains Lunde, are shifted to one side using the Häggloader’s backhoe digging bucket, which is also possible if the dual-digging arms option is chosen. The boulders are then removed from the muck point using the Atlas Copco Scooptram ST1030 LHD or, alternatively, may be left in place and blasted in the next round. “Even if we could get the oversized rocks onto the Häggloader conveyor, it wouldn’t be safe to dump such heavy rocks into the truck’s bucket. Using the LHD for this purpose is the best solution.”

Reducing dust levels

Thanks to the built-in sprinkler system on the Häggloader, dust levels can be considerably reduced at the tunnel face as water is sprayed at the muck point during loading. According to Ronny Bakk, operator of the Boomer drill rigs, the positive impact of the water spraying goes beyond a clearer view for the Häggloader operator. “We have also noticed that using the sprinkler system on the Häggloader has made it easier and faster to accurately position the Boomer rigs, as there is far less dust,” he says. When there is a lot of haulage traffic, an increased level of dust will often impede the correct positioning of the drill rigs, as the use of lasers on the rigs becomes more difficult. “It is important to get a good line in the setup of the drill rigs. The Häggloader has solved this problem as the water sprinkle keeps dust levels low during loading, which makes positioning for drilling a lot easier,” Bakk concludes.

Maintenance and safety

At the onsite service depot, all the machinery, including the Häggloader, is overhauled at regular intervals. Fauskebygg has a service contract with Atlas Copco whereby any maintenance tasks that cannot be solved by the contractor’s engineer can be dealt with by the manufacturer’s service experts. “I’ve worked on overhauling tunneling rigs for many years but had never seen anything like the Häggloader before this project started,” says Svein Rubbås, who has worked as Service Manager for Fauskebygg for 15 years. Apart from operator training, Atlas Copco provided a technician when the Häggloader was delivered who gave instructions on the most basic service aspects.

Rubbås. However, the teeth on the excavator bucket are changed roughly twice per month. Drill steel consumption on the drill rigs has been better than expected, considering a number of critical rock areas at the Govddesåga site. Four drill bits are used per round, after which they are reground at the workshop. Although no incidents have been reported during the tunneling phase of the Govddesåga project, once the headrace tunnel reaches 1.5 km in length, a rescue chamber will be installed in one of the 3.5 m wide niches.

Renewable energy boom

The Nordland region of Norway is known for being one of the least polluted areas of Europe due to its remote location away from the continent’s big cities, yet it provides the topography for a booming industry. The national aim in Norway of boosting hydropower output by 12% by 2020 is well within reach. Innovative techniques to achieve that goal, such as continuous loading, will undoubtedly be sought after as more tunnels are installed with a good working environment and a minimized impact on natural surroundings – for the benefit of clean energy in the future. ◙


265

Hydroelectric power

“Preventive maintenance is what I look at first for all the rigs. We follow the manuals with oil changes and lubrication of parts. I am getting used to the Häggloader, and I try to do whatever work I can on site in the tunnel, such as changing tires, hoses or couplings. Those are easy jobs,” says Rubbås. As the equipment still counts as new, wear and tear is not expected on the Häggloader for several more months, says

The haulage tunnel at the Govvdesåga worksite, at 333 m asl. The new hydropower facility will have an installed capacity of 25 MW.

An extensive grouting plan was required to seal the ground during the construction of the Boyabat Dam in Turkey, due to seismic rock formations.

Grouting triumph at Boyabat Dam

In the “Blue River” valley along the ancient Silk Road, one of Turkey’s largest dams has been built where leakages due to tough rock formations were eliminated thanks to an innovative drilling and grouting plan. Since antiquity and the early days of the Silk Road, the Gökirmak valley in northern Turkey, or “Blue River” valley, has been an important landmark, and the town of Boyabat has played a strategic role as a trade hub. Today, the area is known for a recent milestone in regional development – the construction of the nearly 200 m high Boyabat Dam, part of a hydropower facility that will significantly reduce the country’s dependency on imported foreign energy. It is located 125 km inland from the Black Sea on the river Kızılırmak.

266


Completed after just four years, it became a record-breaking project for Turkey. The reservoir totals 6 000 ha in size with an installed capacity of 513 MW. The power plant is expected to produce 1.5 billion kWh of electricity per annum. It came online in 2012, sooner than predicted, despite the unpredictable, seismic rock formations in the area that presented tough obstacles. The project area is surrounded by the Ilgaz mountains, which reach altitudes of 1 500 m to 1 600 m in the north and west, and by the Kunduz (1 791 m) and Çal (1 732 m) mountains.

BOYABAT DAM, TURKEY

The Boyabat Dam is a concrete gravity dam and is currently the fifth highest dam in Turkey, with a concrete volume that is approximately 2.8 million m3. The surface powerhouse has three Francis turbines of 176 MW each. The facility features a total of 12 tunnels, four used for transportation and eight small cross section tunnels that were used as grouting galleries during construction. Although the investigation phase for the Boyabat Dam project was initiated as early as 1955, construction was postponed because of difficult ground conditions and the steep topography of the surrounding area. Today, the hydropower plant is operational, and the dam stands as a marvel of engineering.

Consolidating and sealing the ground

As the Gökirmak valley is situated just 25 km from an active fault line, the area primarily consists of sedimentary rock with high seismicity that is prone to water leakages. This could cause excessive losses, putting the stability of the dam foundation and its abutments at risk, in addition to the risk of losing water downstream. For construction company Doğuş İnşaat and its subsidiary Ayson, sealing and stabilizing the dam foundation and its abutments was a major challenge and also meant a race against the clock. “We had to accomplish a big project in a very short time. That’s why our needs had to be fulfilled immediately,” says Cumhur Tezel, Project Manager, Doğuş İnşaat. An extensive grouting solution was needed, and Ayson, which was awarded the Boyabat Dam drilling and grouting project, decided to turn to its supplier Atlas Copco for fast and efficient assistance and know-how. The first step toward sealing and stabilizing the dam involved drilling more than 210 km of grout holes from three gallery levels using twelve powerful Diamec U6 core drilling rigs equipped with Atlas Copco in-the-hole tools, including the NO2 wireline core drilling system and SC 6–8 diamond coring bits. Core drilling made it easy to continue the analysis of the rock and secure the quality through reduced deviation and an improved permeability test. Drilling was performed with an average of 400 m per day, or 48 m per day with each Diamec drilling rig, One crew member also achieved an astonishing 4 350 m in total, a unique record and well above the average, using a single SC 6–8 diamond coring bit.

Once drilling was completed, a total of 33 000 m³ of grout was injected into the holes, filling cracks and fissures, to give the dam rock-solid stability. In addition to the drilling solution,

A fleet of 12 Atlas Copco Diamec U6 units were used to drill 210 km of grout holes.


267

Hydroelectric power

Joint venture for grouting

SEALING AND STABILIZING THE BOYABAT DAM

equipped with Cemag agitators and Pumpac grout pumps. By adapting the recipes and quantity, the individual substations were fed the right grout mix to perform curtain, filling and consolidation grouting, with parameters being monitored using the portable Logac electronic recording system.

The right choice

Each station at Boyabat produced up to 11.3 m3 of grout and 3.3 m3 of mortar per hour, and only one of the three Unigrout stations was connected to the sand silo. Grouting was performed in an upstage method with 5 m long sections and holes spaced three meters apart. Downstage grouting could be executed if unstable hole walls were encountered. According to Şahabettin Ağaoğlu, Manager at Ayson’s Drilling Section, the choice of equipment was paramount for success. “We were unable to find any other suppliers to match our expectations. We are highly satisfied with this Unigrout setup. You can’t produce the quality of grout we have achieved if you don´t have the right equipment.” As for the Diamec rigs, the teams achieved 48 m/day per machine, with an average of 2 m/hour using the wireline drillstring against 1.3 m/hour during trials with conventional coring methods, including time spent on permeability tests. Adding new energy to the national grid and jobs to the economy, a lot of people in Turkey have been relying on a positive turn out at Boyabat Dam. Cumhur Tezel was pleased to meet the deadline while stabilizing the dam’s foundations in a comprehensive way. Using three Unigrout Smart L units at grout stations on both sides of the dam, a total of 33 000 m3 of grout was injected for ground stability.

Atlas Copco proposed an innovative modular grouting setup involving the versatile Unigrout Smart L system. In a typical drilling and grouting plan, a central grouting station was installed on each bank to feed the various substations located inside the galleries. For both stations, a set of three Unigrout Smart L were put together, and all control panels were gathered in a silent control room, enabling just one man to operate the whole system and maintain good communication with active crews in the galleries. Producing up to six different recipes of grout and mortar based on the weight of the components, an automatic weight batching DOSAC system was critical to the operation. To inject the grout into the holes, a number of substations were allocated in specially designed niches in the galleries and

268


“I have been working with Atlas Copco for years. We can always contact them for any issue, whether we have questions about design or configuration of equipment, and get a suitable response. Because of this we are very happy.”

Unbroken record

Not only did the short construction time break records for Turkey, Doğuş İnşaat still has the unbroken record in the country for concrete pouring as it achieved a daily capacity of 12 000 m3 and a monthly capacity of 163 000 m3. Apart from extensive curtain grouting from the galleries, a number of grouting techniques were also applied in the hydropower tunnels, including joint grouting, curtain grouting, contact grouting and consolidation grouting. The overall objective was the same – to seal and strengthen the structures – and the assignment was carried out with equal success. ◙

269

Hydroelectric power


A 44.6 km tunnel in Kuala Lumpur will boost the Malaysian capital's supply of potable water, with a capacity of 1 200 million liters per day.

Malaysian water tunnel

presents tough ordeal

At 44.6 km long, it is the longest tunnel in Southeast Asia, designed to bring drinking water to millions of people. But the Pahang Selangor Raw Water Transfer Tunnel has had its fair share of challenges. Kuala Lumpur, the capital of Malaysia, is one of Asia’s most modern cities, but for years it has suffered shortages of potable water (safe for drinking) for its rapidly growing number of citizens, now numbering more than 7 million. However, this problem was due to be solved starting in 2014 when a massive new water tunnel comes on-stream to boost the city’s water reserves at the rate of some 28 m3 per second.

270


Ordinary residents will no doubt take the improvement in their stride, but few tunnel engineers will forget the ordeal that was endured behind the scenes in order to make this project materialize. Known as the Pahang Selangor Raw Water Tunnel, the project began in 2008 with the construction of the Kelau Dam on the Semantan River northeast of the capital. Managed by the Malaysian Ministry of Energy, Green Technology and Water, it includes the construction of a

PAHANG SELANGOR TUNNEL, MALAYSIA

Kelau Reservoir

PAHANG

Kelau Dam

Intake & pumping station Pipe line

SELANGOR

Raw Water Transfer Tunnel

KUALA LUMPUR

ADIT 4

NEGRI SEMBILAN

ADIT 3 M TB

AD

IT 1

TM NA

, 1, 2

3

T

I AD

2

Figure 1 (top left): The Pahang Selangor Raw Water Tunnel is the largest infrastructure project in Malaysia. Top right: The Atlas Copco Boomer L2 C copes with varied rock conditions and considerable water ingress. Figure 2 (bottom left): Eight tunnel sections excavated by drill and blast. Bottom right: The Adit 1 tunnel that leads to the NATM 2 and 3 sections.

24 km2 reservoir and the excavation of a 44.6 km long diversion tunnel – the longest tunnel in Southeast Asia. This conduit is 5.2 m wide and is intended to carry the water to a treatment plant on the outskirts of the city center where it will be treated for both domestic and industrial use.

Major challenges

The design of the tunnel itself is relatively complex, consisting of three TBM (Tunnel Boring Machine) tunnel headings, four drill and blast headings and four adits connected to the main tunnel.However, the real challenge has been the difficult mountain terrain and geological conditions, including blocky rock, overbreak, power outages, extremely high rock temperature and water inflows, that have caused repeated setbacks and frequent threats to progress.

A high level of water ingress, in many cases reaching 10 000 liters per minute, coupled with inconsistencies in the rock formation often slowed down the rate of progress. For example, the fault line known as the Lepoh Fault that runs right across the center of the tunnel alignment displayed serious fracturing on both sides. At one site where the tunnel ran beneath a river, even more water ingress was encountered and required additional stabilization. Various methods of support have been used during the TBM work, including near-zero


271

Water and utility tunnels

Three different types of tunneling methods have been employed on the project: • Tunnel Boring Machine (TBM) • Underground drill and blast • Cut-and-cover

The middle section of the 44.6 km main alignment between Pahang and Selangor, was divided into three sections totaling 34.6 km, and these have been excavated using TBMs. An additional four sections totaling 9.1 km, named NATM 1, 2, 3 and 4, including four adits with cut-and-cover culverts, have been excavated by drill and blast utilizing the New Austrian Tunneling Method (NATM, sequential excavation and temporary rock support) in soft rock formations with the emphasis on ground support.The four adits were, therefore, provided access to the various underground faces for heavy equipment and materials. In addition, these tunnels were equipped with service facilities for drill rig maintenance, concrete mixing and water purification.

POTABLE WATER FOR THE MALAYSIAN CAPITAL

rebound fiber mortar (similar to sprayed concrete but without aggregate), marking the first time that this method has been used outside of Japan.

Computerized drilling

The construction work has been carried out by SNUI, a joint venture of contractors Shimizu Corporation and Nishimatsu Construction of Japan and UEMB and IJM of Malaysia, using face drilling rigs and ground engineering equipment from Atlas Copco. A workforce of more than 1 000 people has been employed on the site, one of whom is Sudhan Bahadur Shreepali, a Nepalese driller with eight years of drilling experience. Although familiar with Atlas Copco Boomer drill rigs, this has been the first timed he has used the computerized model Boomer L2 C. “The drilling here [in the NATM 3 section] has mostly been predictable,” he explains. “The east side rock is pretty good and the west side is less competent. The only real problem was drilling under the river, but this rig made it easier.” Using the Boomer’s computerized functions, Shreepali says it generally took about two hours to drill a round, and working two 12-hour shifts per day, the crew was normally able to advance the tunnel at the rate of 8 m per day. Three Boomer L2 C rigs equipped with COP 1838 rock drills have been responsible for most of the drilling, using Secoroc 105 mm bits for drilling pilot holes to create a cut for initial blasts and 45 mm bits for blastholes. Takashi Kawata, Project Manager at the SNUI joint venture, points out that despite the difficulties, the NATM segments were completed either according to plan or as much as three months ahead of schedule. The NATM 3 section suffered delays during the drive under the river but quickly recovered once it reached the other side. The NATM 4 section was also hampered by sections of soft rock conditions, although for the most part the drillers have been drilling in granite.

Exceeding expectations

Drilling at the NATM 2 section, using Boomer L2 C drill rigs, advanced at a rate of 149.4 m per month despite mountainous terrain.

272


Kawata also pointed out that the rate of advance with the Boomer L2 C was 10% better than expected. “We have been getting good results with drilling and blasting,” he says, adding that in some months the rigs’ performance far exceeded expectations. For example, average productivity for the NATM 2 section was set 138.3 m per month but actual productivity averaged 149.4 m month. In addition to the drill rigs, an Atlas Copco COP 1838 rock drill has been used for drilling 76 mm probe holes ahead of the TBMs in the main tunnel drives while all rock tools used on site are also from Atlas Copco. SNUI has also employed nine Locomotive DH10 units and one DHD15 unit from Atlas Copco for construction materials transport in the TBMs. With modern excavation technology and well-trained drilling crews, the citizens of Kuala Lumpur can look forward to ample supplies of potable water for many years to come. ◙

273

Water and utility tunnels


This is what a well-designed access tunnel should look like. Tommy Forsgren, Production Manager, Skanska

Stockholm's new underground depot for subway trains is excavated using Atlas Copco Boomer XE3 C (pictured) and Boomer L2 C drill rigs.

Train depot rises below Green Capital

Stockholm, a city in rapid transformation, looks to a vast underground complex for subway trains as a key investment in the future. Situated on a cluster of islands on the Baltic coast, the capital of Sweden is traditionally known as "Venice of the North" and draws attention for having the world's largest archipelago. It also boasts the Nobel Prize ceremony, clean air and water and a general high standard of living where sustainability concepts permeate society. In fact, in 2010, Stockholm became the first city to be designated the title “Green Capital of Europe” by the EU – now a

274


coveted award – in recognition of the city’s strong focus on green solutions. Moreover, this philosophy is being mirrored in a number of important construction and tunneling projects in and around the city. With an influx of 35 000 new residents every year, Stockholm is experiencing unprecedented population growth and, for this reason, the greater region is in the midst of a major expansion phase. According to official estimates by the city’s Chamber

NORSBORG DEPOT, SWEDEN

Steady progress: The Boomer XE3 C in action drilling 5.8 m long blastholes with a penetration rate of 2.5 m/min. "The rod handling system and carousel are very reliable," says operator Marián Richtárik.

of Commerce, Stockholm will by 2030 outpace London to become the fastest growing city in Europe – expanding six times faster than Paris. Politicians, city planners and contractors are engaged in a comprehensive redevelopment scheme involving everything from new housing and business districts to upgrading the city’s road and rail networks. The City Link rail line for commuter travel is well underway, and another more recently initiated project is the construction of an underground depot for subway trains – the largest of its kind in Sweden – in a southwestern suburb called Norsborg.

Upgrading the Red Line

SL’s investment, which also includes a new signaling system, aims to increase passenger capacity by 30% on the Red Line, meaning higher frequency of travel with 48 trains instead of 37 departing every hour. When completed, the Norsborg

The depot design is based on three main tunnel sections of large dimensions that measure 9 m high and 22 m wide, as well as a number of smaller adjacent tunnels and caverns. The stabled trains will stretch for a total length of 3.7 km inside the rock of the Eriksberg ridge in the municipality of Botkyrka, with tracks that loop round the Norsborg end station. When deployed for use on the Red Line, the trains will exit fully serviced and cleaned through blasted access tunnels, ready to cater to the city’s new public transport needs.

Underground depot: key benefits

Although underground train depots are less common than surface depots, they provide a number of important advantages such as reduced land appropriation. Only 200 meters of land will be required for surface structures such as office buildings. Furthermore, the risk of costly vandalism is significantly lowered due to the enclosed and restricted space


275

Utilization of Underground Space

More inhabitants mean greater demands on public transport. The Norsborg Depot (Norsborgsdepån) is being built to accommodate 27 new trains commissioned by Stockholm’s public transport entity SL that will be due for introduction in 2017 on the subway network’s Red Line.

Depot will be a state-of-the-art rail complex featuring covered stabling areas, washing facilities and fully equipped workshops for repair and maintenance – with most of the utilized areas located underground.

THE NORSBORG DEPOT: A GREEN CONSTRUCTION SITE

Green construction: Ventilation output is adapted to each activity using Atlas Copco fans equipped with a frequency inverter system. This enables up to 50% reduction in energy consumption. (Note: The ventilation system from Atlas Copco is now named Serpent Ventilation System.)

inside the rock. Another major benefit for SL’s new depot is the rock’s natural temperature of +12 degrees Celcius C all year round. This means that wear and tear on the trains, especially during the cold winter months when snow and ice are frequent, will be drastically reduced.

Unigrout Smart grouting platform. Using this fleet, Skanska aims to achieve a production target of 4 000 tonnes per day, provided that the local traffic situation permits the necessary haulage.

The Norsborg Depot tunneling assignment has been awarded to the Swedish international contractor Skanska, which, over a two year period, will be tasked with drilling, blasting and hauling away more than 330 000 m3 of rock. The work site was officially inaugurated in September 2013 during a ceremony where the blessing of St. Barbara, the Patron Saint of tunnelers, was bestowed on the project by a priest. The project quickly progressed with the first construction element, a 250 m long access tunnel that will enable Skanska’s tunnelers to reach the main construction site 18–37 m below the surface.

Adapted to future rail

“We remove about 20 000 tonnes of rock per week from the ridge, or 1 500 m3 per day,” explains Tommy Forsgren, Production Manager at Skanska who oversees a team of 28–30 people per shift, recruited from the company’s division in Slovakia. The excavation work is being carried out using a fleet of Atlas Copco equipment: two Boomer XE3 C drill rigs, one Boomer L2 C, a MEYCO Potenza sprayed concrete rig, an Atlas Copco ventilation system with frequency inverter, and a

276


The blueprint for the Norsborg Depot involves a high degree of complexity, partly due to a vast amount of underground installations and partly because it needs to cater to future developments in rail. This includes preparations for the advent of driverless trains which, as Forsgren explains, is the reason for the unusual size of the tunnels and a two-level design. “The idea is to prevent staff from crossing over the tracks by foot when driverless trains are introduced, so that’s why stairs are being built on either side of the tunnels leading to an upper level where SL’s people can move around without concern for their personal safety,” he says. At the site, the Skanska crew works two shifts per day on a running schedule, six days per week. Drilling is only permitted between 7 a.m and 7 p.m due to the risk of structureborne noise that can affect nearby buildings, including a school and a day care center. Blasting is normally carried out twice per day, at 11 a.m and then again at around 8 p.m, and


Complex drill plans are produced for each working shift using Atlas Copco's Underground Manager system. These are received by the computerized Rig Control System (RCS) fitted on the tunneling equipment, which also provides a range of automated drilling functions.

is followed by haulage operations that continue throughout the night. Forsgren comments: “We evaluate our work and revise the placement of vibration sensors every second week together with SL and the local authorities. So far we have kept vibrations well below the limit of 70 mm/s per 10 meters, barely reaching 50% of that at maximum.” The first excavated section of the access tunnel covered a face area of 170 m 2 divided into benches, with around 220 holes drilled using the Boomer XE3 C drill rigs. The rigs feature three booms equipped with Atlas Copco COP 3038 rock drills and 48 mm diameter bits. The holes are blasted using a Site Sensitive Emulsion (SSE) blasting agent with a Rheomex matrix.

Tough logistics

While a demanding aspect, Forsgren points out that a far greater challenge is the logistics of such a large project, especially in the initial phase where haulage operations can be tricky due to the lack of maneuverable space. This temporary

Following the completion of the access tunnel, Skanska will begin to develop stabling tunnel No. 1 and No. 3 in sequence (see photo next page) and then the middle section tunnel No. 2. Each tunnel section is approximately 300 m long. The logistics of the operations not only relate to the tunneling team and machinery but also to progress reports and coordination with local authorities and other contractors involved. Apart from housing, businesses, schools and urban infrastructure located directly above the depot, there is also a protected nature reserve not far from the work site. This has led to strict regulations imposed to safeguard the natural environment and to avoid disturbing local residents.

Smooth excavation

In order to meet the high requirements for safety, quality and production speed, Skanska has employed two Boomer XE3 C drill rigs, one of which is almost new. They are used interchangeably for multiple drilling applications: drilling 5.8 m long blastholes, 24 m long holes for injection grouting, short boltholes for rock bolts and large diameter opening holes. Drilling has, according to the tunneling team, progressed


277


Due to the scope of the project, the volume of rock to be extracted at the face varies greatly. This has meant that a large number of drill plans have to be generated using Atlas Copco’s Underground Manager system. The number is likely to increase as excavation begins on the main tunnel sections.

problem in the access tunnel has meant that haulage trucks destined for Skanska’s crushing facilities some 13 km away, have had to enter the tunnel and make a full turn in niches before getting a full payload of waste rock.

THE NORSBORG DEPOT: A GREEN CONSTRUCTION SITE

With three main tunnel sections measuring 9 m high and 22 m wide, the Norsborg Depot construction involves comprehensive logistics. Tommy Forsgren, Production Manager, points out the access tunnel where more than 330 000 m3 of rock will be hauled away over a two year period.

smoothly. In addition to blasthole drilling, this includes probe drilling which is a fixed element in the production cycle. It involves the drilling of strategically placed, 24 m long holes that are measured for water loss, in order to work proactively with rock support. If necessary, the rock is sealed with injection grouting as soon as 10–20 holes have been drilled using the two outer booms equipped with Rod Handling System (RHS). The environmental rules stipulate that no more than 100 liters of water ingress is permitted per 24 hours. “If the water loss rate exceeds 12 liters per minute we go ahead and drill a complete fan of grout holes around the tunnel profile. So far we’ve only had to do seven fans, which is low. The tunnel has been exceptionally dry,” says Forsgren. The microcement used for injection grouting is prepared with the Atlas Copco Unigrout Smart grouting platform and is injected into the rock with a maximum pressure of 20 bar. No more than 800 liters of grouting is injected per hole because the cement may then seep into adjacent voids in the rock, which may affect stress fields and potentially cause further instability. Together with SL and other contractors involved in the project, Skanska makes continuous efforts to keep the general

278


public well-informed of the construction plans. All residents in the area can also choose to receive text message notifications sent out 30–45 minutes before blasting takes place. As delay times are set up to 9 000 ms, one blast can last for a full nine seconds. Jörgen Crilén, Plant Manager at Skanska, also works closely with the Slovakian team of drillers. Together with Forsgren he gives briefings every morning at the site office regarding production goals and safety issues. He also makes sure that efficiency levels and the availability of equipment are kept high. The Boomer XE3 C rigs, says Crilén, typically achieve an average penetration rate of 2.5 m/min and 1.5–2.0 m/min for the long holes (24 m). “This enables us to drill approximately 1 200–1 300 drill meters per 12-hour shift, with each hole taking about 1.5–2 minutes to drill. Our Slovakian team at the site is comprised of very skilled drillers who are used to working with the Boomer XE3 C rigs. They know the crucial importance of straight holes and perform to that measure.” The hard “Stockholm granite” which is common for the region, has been easy to drill, according to the Boomer XE3 C operators. Says operator Marián Richtárik: “The rod handling


system and carousel on the drill rig are very efficient and reliable. It also has feeders that work well in small, narrow places, and the drill hammers are both fast and strong.” His designated rig has 95 000 drill meters on the clock and has been drilling blastholes with a penetration rate of 3.2–3.8 m/min. In order to facilitate communication, all software menus and functions in the computer system of the Boomer rigs, known as the Rig Control System (RCS), have been translated to Slovakian with the help of Atlas Copco. In preparing for the project, the drilling team also took part in a three-day training course at Atlas Copco´s facilities in Örebro, Sweden. The course brought the team up to speed on the latest developments of the RCS system, including positioning functions and automation levels.

Full service contract

Skanska decided at an early stage to opt for a full service contract applied to all of its Atlas Copco equipment used at the Norsborg Depot. This has meant that a service technician has been available on site every day, ready to assist with any problems. “The service agreement has been an excellent resource,” says Forsgren. “We had some difficulties early on with the carousels and rod handling systems. The problems were solved quickly which prevented any real downtime and any halt of production.” The service technician also takes care of all scheduled maintenance meaning that oil filter changes and many other procedures are carried out according to the service manual. Daily routine procedures include the checking of hydraulics, brakes and lights on the rigs. In addition to service, Skanska makes sure that the spherical button bits including bits from Atlas Copco Secoroc, are reground every 150–200 drill meters in order to achieve maximum economy. The lifespan of the drill bits, including regrinding, is roughly 500–700 drilled meters. “All of this gives us minimized downtime. Our service engineer is also sometimes present as an observer in the Boomer cabin, especially when we drill the 24 m long holes using the rod handling system.”

Green construction site

The green approach adopted by Skanska encompasses everything from a heavily restricted use of chemicals to responsible waste management and a reduced consumption of energy and

water. In terms of reducing energy consumption, Skanska has opted to install the Atlas Copco ventilation system equipped with frequency inverter. This means that the ventilation output frequency can be adapted to the needs of each activity: drilling, blasting, rock support and haulage. This enables potential energy savings as high as 50% compared with conventional systems. “We have also installed four ventilation tubes connected to the fans that are tailor-made to the rock environment at Norsborg. This prevents fresh air from leaking out and further reduces waste,” says Jörgen Crilén. Rigorous monitoring of the operations, says Crilén, is the key to maintaining lean yet efficient production. This requires modern technology, such as automatic GPS transmitters for measuring water, and a proactive approach that takes every detail into account. For instance, Skanska has installed a treatment system that collects water from the ground and runs it through a filtering system to separate oils and harmful residue, typically from spillages during maintenance at the onsite workshop. This system protects the area from being contaminated in any way, and the same applies to residue water from drilling, which is also treated. Nitrogen sedimentation, however, is difficult to treat but levels are improving, says Crilén. “Basically, we track everything.


279


Scandinavian companies have a strong track record when it comes to Corporate Social Responsibility (CSR) and Skanska is considered a leader in this field. The company is known internationally for giving top priority to issues such as health and safety, labor rights and, not least, sustainability at all its work sites – and the Norsborg Depot is no exception.

Upgrading the subway: Stockholm's new underground train depot will feature covered stabling areas (3.7 km in total), washing facilities and workshops or repair and maintenance.

hand as if you weren’t wearing them. As a result, we’ve seen a huge drop in the number of hand injuries throughout our organization.” When it comes to securing the environment, a well-designed rock support system cannot be overemphasized. For the cross center tunnel, a two-level excavation sequence will be performed, meaning that the upper section will be excavated first so that rock bolts can be installed using the Boomer XE3 C or Boomer L2 C. The next step is to apply sprayed, wet-mix concrete on the walls using the MEYCO Potenza sprayed concrete rig, which is fully mobile and remote controlled so that operators can be kept away from the main hazard areas. The lower section is then drilled and blasted in benches.

Skanska's drill rigs are employed with a full service contract from Atlas Copco. The production target is set at 4 000 tonnes per day.

No chemicals are brought to the site that haven’t been crosschecked with our comprehensive chemicals database and approved for use. We monitor water levels, energy and fuel consumption. Our diesel storage tank has a system for measuring consumption and correlating the data with each piece of machinery, which is equipped with an ID tag. When the tank needs re-filling, it automatically sends a notification to our supplier, who dispatches a refueling truck.” These diligent measures have enabled the Norsborg Depot to achieve a Silver status in Skanska’s internal sustainability program, where work sites are graded according to a wide range of parameters. Both Forsgren and Crilén are confident as they only have eight points to go before achieving Gold status – the full “Green Construction Site” designation.

Safety first

As part of its total solution for construction, Skanska works tirelessly with safety issues and on finding new ways to improve. Partly, this is achieved by continuously investing in modern machinery such as the Boomer rigs with FOPS/ROPS protected cabins. Such equipment also features advanced cameras, sensors, hazard lights and sound alarms. Added to this is a safety-focused philosophy in terms of all standard gear for tunnelers – helmets, protective glasses, boots, jackets and gloves – which are all of the latest and most reliable type. Developments in these areas, such as new materials use, have also enabled Skanska to achieve a first class record for safety. Hands and fingers, says Crilén, are typically at risk. “Operators would previously take off their gloves because they were just not practical at times, such as when unscrewing a nut or bolt. But modern gloves are both highly durable and flexible at the same time, giving the same mobility to your

280


Furthermore, as the tunnels are advanced, Skanska will be deploying a rescue chamber for those worksite areas that only have one exit. All personnel have also been given ID tags that communicate with sensors at the access tunnel entrance, which enables the site managers to monitor the presence of each authorized person. Another important aspect of safety, says Forsgren, is to establish a good relationship with emergency services. “We invited a large team from the fire department and other first responders to the site for a tour so they could familiarize themselves with the environment. This enabled us to evaluate the response time and also allocate strategic water supply sources as precautionary measures.”

A distinguished project

Beyond emergency personnel, many more have visited the Norsborg Depot since construction began. A keen interest in the project has come from both the construction industry and the general public, who will also benefit from refurbishments of the subway station itself as part of the upgrade. “We had a delegation of professionals from Russia visiting who wanted to learn from our work, as they’re planning for the construction of subway tunnels in Moscow that will extend over 100 kilometers,” says Forsgren. In the week following our visit, the Skanska team was expecting representatives from Stockholm’s next major infrastructure endeavor – the long-awaited Stockholm Bypass for road traffic that will connect to the E4 highway. “We take pleasure in sharing our expertise. This is what a well-designed access tunnel should look like,” Forsgren concludes with a hint of pride. The Bypass will stretch for 21 km of which 18 km will extend through tunnels. With the Norsborg Depot access tunnel, it would seem Skanska has only just begun yet already achieved a world-beating example. ◙

281



Produced by: Atlas Copco Rock Drills AB, SE-701 91 Örebro, Sweden, tel +46 19 670 70 00 Publisher: Lars Senf, [email protected] Production Manager: Johannes Hansson, [email protected] Editor: Julian Greenwood, [email protected] Application Specialists and Editorial Advisors: Johannes Hansson, [email protected], Gunnar Nord, [email protected] To order a personal copy please contact your local Atlas Copco company by visiting www.atlascopco.com or www.miningandconstruction.com Reproduction of individual articles only by agreement with the publisher. Edited by: Greenwood Communications, Sweden Designed and typeset by: ahrt, Örebro, Sweden Printed by: Ineko, Stockholm, Sweden Legal notice © Copyright 2015, Atlas Copco Rock Drills AB, Örebro, Sweden. All product names in this publication are trademarks of Atlas Copco. Any unauthorized use or copying of the contents or any part thereof is prohibited. Illustrations and photos may show equipment with optional extras. No warranty is made regarding specifications or otherwise. Specifications and equipment are subject to change without notice. Consult your Atlas Copco Customer Center for specific information.

282

ATLAS COPCO UNDERGROUND CONSTRUCTION

Atlas Copco Underground Construction

UNDERGROUND CONSTRUCTION

COMMITTED TO SUSTAINABLE PRODUCTIVITY

Printed matter no. 9851 3427 01

www.atlascopco.com

A global review of tunneling and subsurface installations

2015

We stand by our responsibilities towards our customers, towards the environment and the people around us. We make performance stand the test of time. This is what we call – Sustainable Productivity.

FIRST EDITION 2015

AtlasCopco Underground Construction

Recommend Documents