Presas Carpi Lámina Pvc

CARPI PATENTED GEOMEMBRANE SYSTEMS *****

GEOMEMBRANE FACING ROCKFILL DAMS (GRFD) CASE HISTORIES

Sar Cheshmeh tailings dam, Iran - 2008

Murdhari dam, Albania - 2013

Nam Ou VI dam, Lao PDR – 2014&2915

Kouhrang headpond, Iran - 2004

February 2015

-----------------------------------Waterproofing Specialists and Contractors-----------------------------------

Geomembrane Facing Rockfill Dams – GFRDs

CARPI TECH

TABLE OF CONTENTS 1

CARPI EXPERIENCE ........................................................................................... ........................................................................................................................... ................................ 3

2

CARPI UPSTREAM EXPOSED GEOMEMBRANE SYSTEMS FOR NEW ROCKFILL DAMS 6

2.1 2.2 2.3

UPSTREAM WATER BARRIER ....................................................................................................... ............................................................................................................. ....... 6 TO THE DAM FACE FACE ................................................................................... A NCHORAGE TO ........................................................................................................ ..................... 8 PERIMETER SEALING ..................................................................................................... ....................................................................................................................... ................... 11 ®

3 GFRD PROJECTS WITH SIBELON ANCHOR STRIPS ON EXTRUDED CURBS: CASE HISTORIES HISTORIES ..................................................................................................................... ................................................................................................................................................... .............................. 11

3.1 SAR CHESMEH TAILINGS DAM RAISING , IRAN 2008 ........................................................................ 11 3.2 UPPER PART OF R UNCU UNCU GFRD, R OMANIA OMANIA 2014 ............................................................................. 13 3.3 NAM OU VI, LAO PDR, FIRST STAGE COMPLETED IN NOVEMBER 2014, WHOLE COMPLETION IN DECEMBER 2015 ..................................................................................................................................... .......................................................................................................................................... ..... 14 3.4 TAILINGS DAM , GFRD, PERU, STAGE 1A COMPLETED IN 2014 ...................................................... 16 IVER DAM , AUSTRALIA ........... 18 3.5 GFRD PROJECT APPROVED AND TO BE CONSTRUCTED : DUGALD R IVER ® 3.6 ADVANTAGES OF THE SYSTEM WITH SIBELON ANCHOR STRIPS ON EXTRUDED CURBS .............. 18 ®

4 GFRD PROJECTS WITH SIBELON ANCHOR STRIPS EMBEDDED IN TRENCHES: CASE HISTORIES HISTORIES ..................................................................................................................... ................................................................................................................................................... .............................. 19

4.1 4.2 4.3 4.4

K OUHRANG ..................................................................................... 19 OUHRANG HEADPOND GFRD, IRAN 2004 ..................................................................................... MURDHARI GFRD, ALBANIA 2013 ................................................................................................. 22 LOWER PART OF R UNCU ........................................................................... 23 UNCU GFRD, R OMANIA OMANIA , 2014 ........................................................................... GFRD AT THE 18 WATER SAVING BASINS OF THE PANAMA CANAL EXPANSION PROJECT , 2014 ..................................................................................................................................................... 25 AND 2015 ..................................................................................................................................................... 4.5 GFRD PROJECT APPROVED AND TO BE CONSTRUCTED : BULGA, AUSTRALIA ................................. ................................. 26 ® 4.6 ADVANTAGES OF THE SYSTEM WITH SIBELON ANCHOR STRIPS EMBEDDED IN TRENCHES ......... 28 4.7 A PIONEER PROJECT : ALENTO COFFERDAM , ITALY 1988 ................................................................ ................................................................ 28 5

GFRD PROJECTS WITH DEEP EARTH/GROUTED ANCHORS: CASE HISTORIES ........... 29

5.1 5.2 5.3 5.4 5.5 6

PROJECTS WITH UPSTREAM COVERED GEOMEMBRANE: CASE HISTORIES .............. 35

6.1 6.2 7

VAITÉ EARTHFILL DAM , FRENCH POLYNESIA 2011...................................................... 2011......................................................................... ................... 29 FILIATRINOS , GREECE, 2015 ......................................................................................... ............................................................................................................ ................... 31 AMBARAU , DEMOCRATIC R EPUBLIC EPUBLIC OF CONGO, TO BE CONSTRUCTED ......................................... 33 DEEP GROUTED ANCHORS AT CANALS ’ EMBANKMENTS ......................................................... ................................................................. ........ 33 ADVANTAGES OF THE SYSTEM WITH DEEP ANCHORS ...................................................................... ..................................................................... 34 BOVILLA , ALBANIA 1996 ................................................................................................................ 35 JIBIYA, NIGERIA 1997 ...................................................................................................................... ...................................................................................................................... 36

PROJECT WITH CENTRAL GEOMEMBRANE: GEOMEMBRANE: GIBE III COFFERDAM COFFERDAM ............................... 36

8 THE EXPOSED GEOMEMBRANE SYSTEM AS EXTERNAL WATERSTOP: ANGOSTURA CFRD, CHILE 20012 ...................................................................................................... .................................................................................................................................... .............................. 38

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1

CARPI TECH

CARPI EXPERIENCE

Carpi, established in 1963, is today the oldest company in the world specialized in waterproofing of hydraulic structures with with geomembrane systems. systems. Carpi provides turn-key turn-key projects including design design of he geomembrane system, supply of materials, and installation. Carpi geomembranes and geocomposites, known under the trademark SIBELON ®, are produced exclusively for Carpi under ISO 9001 certification. Exclusive proprietary formulation and computer-controlled production ensures constant constant properties and high performance performance of the waterproofing liner. SIBELON ® geomembranes and geocomposites have been installed by Carpi, using its patented anchorage systems, on all types of hydraulic structures, worldwide, worldwide, since 1970 (the first installation was made by Carpi in 1976 and it is still in service), and include: all types of dams, reservoirs, canals and hydraulic tunnels. The table below reports the cumulated years of experience of Carpi in waterproofing hydraulic structures. Type of structure

DAMS RESERVOIRS RESERVOIRS CANALS HYDRO TUNNELS TOTAL

Number of Quantity of geomembrane Cumulated years of experience* hydro projects* installed* [m2] (number of projects multiplied by number of years in operation) 139 1,069,427 1,566 31 1,009,786 505 37 1,405,773 639 14 49,039 276 221

3,534,025

2,986

* as of December 2014. In dams, Carpi experience includes all types of dam: rockfil and earthfill dams, RCC dams, concrete (gravity, buttress, arch, multiple arch) and masonry dams. In fill dams, Carpi has applied its waterproofing geomembrane systems to construction of new dams as well as to rehabilitation of existing dams where the upstream face had lost its waterproofing function. Rehabilitation has been made in the t he dry and also underwater. In construction of new rockfill dams the watertight geomembrane is generally installed as an exposed upstream facing, to construct what is known as a Geomembrane Facing Rockfill Dam (GFRD). In alternative, the upstream geomembrane can be ballasted, or the geomembrane can be installed in central position, to construct a geomembrane geomembrane core. All these three options have have been successfully applied. The three options are outlined in the scheme that follows: at top right and bottom left, the usptream exposed geomembrane system (GFRD) respectively with extruded curbs and without extruded curbs, at top left the upstream covered geomembrane system, at bottom right the geomembrane core system.

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This documents focuses on Carpi upstream exposed geomembrane system (GFRD), discussing some significant case histories presenting some site-specific variations. Some information on dams with covered geomembrane facing, central geomembrane, and on Carpi external waterstop system, is also presented. Here below, a summarising table of the projects listed in this document,in the order in which they are presented.

Dam's name

Country

Type

Height [m]

Position of geomembrane

Sar Cheshmeh

Iran

Tailings

20

Upstr.exp.

Runcu Upper part Lower part

Romania

Rockfill

91

Upstr.exp.

Nam Ou VI

Lao PDR

Rockfill

88

Upstr.exp.

Peru

Tailings

48 (230 when completed)

Upstr.exp.

Australia

Tailings

40

Upstr.exp.

Kohrang

Iran

Rockfill

16.5

Upstr.exp.

Murdhari

Albania

Earthfill

36

Upstr.exp.

Panama

Rockfill

25

Upstr.exp.

Bulga

Australia

Tailings

21

Upstr.exp.

Alento

Italy

Earthfill

21

Upstr.exp.

Earthfill

23

Upstr.exp.

Hardfill

55

Hardfill Rockfill Earthfill Rockfill Rockfill

GFRD Dugald River

Panama Water Basins

Vaité Filiatrinos Ambarau Bovilla Jibiya Gibe III Angostura

Canal Saving

French Polynesia Greece DR of Congo Albania Nigeria Ethiopia Chile


Type of anchoring

Anchor strips on curbs Anchor strips on curbs Anchor strips in trenches Anchor strips on curbs Anchor strips on curbs Anchor strips on curbs Anchor strips in trenches Anchor strips in trenches Anchor strips in trenches, deep anchors Anchor strips in trenches Anchor elements

2

m

Use of dam

40,000

Mining

36,900

Hydro

38,000

Hydro

166,000

Mining Mining

16,500

Hydro

8,005

Hydro

600,000

Navigation locks

9,450

Mining

16,500

Cofferdam

Deep anchors

3,800

Hydro

Upstr.exp.

Deep anchors

10,200

Irrigation

21

Upstr.exp.

Deep anchors

2,800

Hydro

91 21.10 50 32

Upstr. Cov. Upstr. Cov. Central Ext. Waterstop

Ballast Ballast Ballast Mechanical

9,138 165,000 15,213 4,560

Multipurpose Irrigation Cofferdam Hydro

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Geomembrane Facing Rockfill Dams – GFRDs 2

CARPI TECH

CARPI UPSTREAM EXPOSED GEOMEMBRANE SYSTEMS FOR NEW ROCKFILL DAMS

In rockfill dams, one main challenge is to construct a watertight barrier that will not fail under the significant settlements and/or differential movements between the deformable dam body and the rigid concrete structures (plinth, spillway, outlets) that often occur. Carpi upstream geomembrane systems are based on the concept of providing a flexible watertight barrier that can elongate well beyond the maximum expected deformations of the dam body. The flexible water barrier is anchored to the dam face with a flexible anchorage system, and at concrete boundaries with a perimeter seal designed to resist differential settlements while mantaining watertightness. 2.1

Upstream water barrier

The upstream water barrier is a SIBELON® geocomposite. SIBELON® is a flexible composite synthetic material (geocomposite) consisting of a Polyvinylchloride (PVC) geomembrane providing watertightness, and of a backing anti-puncture geotextile heat-bonded during manufacturing to the geomembrane. The PVC geocomposites and geomembranes used by Carpi, known under the trademark SIBELON®, are produced exclusively for Carpi under ISO 9001 certification. The assets of SIBELON® geocomposites and geomembranes are: - Very low permeability (<10-6 m3/m2/day EN 14150) - Elastic behaviour in uni-axial and multi-axial tension, with large ultimate elongation (≥ 230% according to EN ISO 527/4 standards) - High resistance to puncturing, bursting, and impact - Proven excellent performance in harsh climates (extreme temperatures, both high and low) - Proven high resistance to UV radiation (100 years in exposed posiiton, according to the latest feedback form research and the field) - Constant properties and performance, because of production under controlled exclusive proprietary formulation One main reason for selecting a PVC geocomposite or geomembrane instead than other types of gemembranes is its tensile behaviour. The tensile behavior of the geomembrane in a fill dam is extremely important, especially at locations where the geomembrane supported by an embankment is connected to a rigid structure (e.g. a concrete plinth). A study by Giroud & Soderman (1995) has shown that an appropriate combination of tensile strength and strain is essential. This optimum combination depends on the shape of the tension-strain curve of the geomembrane. It is quantified by the co-energy of the tension-strain curve: the co-energy is the area between the tension-strain curve and the tension axis (i.e. the vertical axis). The coenergy quantifies the ability of a geomembrane to withstand differential settlements. Only the continuously increasing portion of the tension-strain curve can be used in the determination of the co-energy. Figure A1 that follows shows the increasing portion of the tension-strain curve of two considered geomembranes: a PVC geocomposite and a Low Linear Density Polyethylene (LLDPE) geomembrane. If a High Density Polyethylene (HDPE) geomembrane is considered, its co-energy in comparison to a PVC geocomposite is even less. Since the tension-strain curve of an HDPE geomembrane has a yield peak at a strain of 12% to 15%, beyond the yield peak an HDPE geomembrane ceases to function from a mechanical standpoint (Giroud 1984). Therefore, the co-energy of an HDPE geomembrane is calculated up to the yield peak, as shown in Figure B1 that follows.


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Figure A1. Increasing portions of the tension-strain curves of a 1.5mm thick LLDPE geomembrane and a composite PVC geomembrane 2mm thick . Courtesy of JP Giroud.

Figure B1. Increasing portions of the tension-strain curves of a 2mm thick HDPE geomembrane and a composite PVC geomembrane 2.5mm thick . Courtesy of JP Giroud. .

A geomembrane can successfully withstand a differential settlement if the required geomembrane co-energy that corresponds to the differential settlement is less than the allowable geomembrane co-energy. The coenergies associated with these above tension-strain curves are shown in Figures A2 and B2 respctively. It is clear from these figures that the co-energy associated with the composite PVC geomembrane is significantly greater than the co-energy associated with the LLDPE geomembrane, and even greater than the co-energy associated with the HDPE geomembrane. This means that the factor of safety with respect to stresses associated with differential settlements is significant higher in the case of a composite PVC geomembrane than in the case of an LLDPE geomembrane or an HDPE geomembrane. An increase in LLDPE and HDPE geomembrane thickness would not change this conclusion.


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Figure A2. Co-energy of a composite PVC geomembrane 2mm thick (pink area) and of a 1.5mm thick LLDPE geomembrane (area limited by purple lines). Courtesy of JP Giroud.

Figure B2. Co-energy of a composite PVC geomembrane 2.5mm thick (pink area) and of a 2mm thick HDPE geomembrane (purple area) . Courtesy of JP Giroud. .

The composite PVC geomembrane has a co-energy (i.e. area between the tension-strain curve and the tension vertical axis) that is much larger than the co-energy of the LLDPE geomembrane and even larger than the co-energy of the HDPE geomembrane. Therefore composite PVC geomembranes have a higher ability to withstand differential settlements than LLDPE and HDPE geomembranes. 2.2

Anchorage to the dam face

The SIBELON® PVC geocomposite is anchored to the dam face so to resist uplift by back-pressures, wind and waves. Depending on the methodology of dam construction, different anchorage systems are available. All systems described here after are Carpi patents: 1. In rockfill dams where the finishing layer is formed by extruded porous concrete curbs: the face anchorage system consists of SIBELON® geocomposite anchor strips embedded in the extruded porous concrete curbs that form the stable finishing layer of the embankment. The SIBELON® anchor strip fixed to one curb overlaps the SIBELON® anchor strip fixed to the underlying curb, and


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the overlapping strips are heat-seamed to form continuous anchor lines (see schemes below). The distance between the anchor lines is designed in function of the design uplift loads.

Anchorage system for a dam adopting the method with extruded porous concrete curbs: at left section with the SIBELON® ancor strips embedded in the curbs, at righ tthe same section after the waterproofing SIBELON ® geocomposite has been placed on the PVC anchor strips.

The SIBELON® geocomposite liner is then deployed over the SIBELON® anchor lines and watertigth heatseamed to them. This Carpi patent is presented in ICOLD Bulletin 135 “Geomembrane Sealing systems for dams – Design principles and review of experience”, and further described in chapter 3 “GFRD projects with SIBELON® anchor strips on extruded curbs: case histories”.

2. In rockfill dams where the finishing layer is NOT formed by extruded porous concrete curbs: depending on site-specific construction method and type of uppermost layers, the anchorage system can be of two types:


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Geomembrane Facing Rockfill Dams – GFRDs o

CARPI TECH

a) The face anchorage system consists of SIBELON® geocomposite anchor strips embedded in trenches excavated in the base layer at site-specific spacing. The trenches are generally backfilled with draining material (porous concrete or granular material). The SIBELON® geocomposite liner is then deployed over the SIBELON® anchor lines and watertigth heatseamed to them, as for the extruded porous concrete curbs method. This system is further described in chapter 4 “GFRD projects with SIBELON® anchor strips embedded in trenches: case histories”.

Typical anchorage trench.

o

b) The face anchorage system consists of deep anchors that are driven into the embankment after it has been completed, according to site-specific patterns. The SIBELON® geocomposite liner is then deployed and punched over the anchors. A stainless steel disk, an anti-puncture geotextile, and a SIBELON® geomembrane, cover watertight heat-seamed to the SIBELON® geocomposite, ensure watertightness at the anchors. Deep earth anchors, or deep grouted anchors, are the available configurations. This system is further described in chapter 4.4 “GFRD projects with deep earth/grouted anchors: case historiesGFRD projects with SIBELON® anchor strips embedded in trenches: case histories”.


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CARPI TECH

Types of deep anchors. 2.3

Perimeter sealing

At all peripheries, the SIBELON® geocomposite liner is anchored by perimeter seals to avoid that water can infiltrate behind the liner. Perimeter seals are designed to be watertight to the expected water pressure with the established factor of safety. The case histories that follow will describe how the seal is designed in function of the underlying substrate. 3

3.1

®

GFRD PROJECTS WITH SIBELON ANCHOR STRIPS ON EXTRUDED CURBS: CASE HISTORIES Sar Chesmeh tailings dam raising, Iran 2008

Sar Cheshmeh existing tailings storage, owned by National Copper Industries Co., included a 75m high main embankment consisting of an inclined clay core and of outer colluvial gravel shells. The production escalation involving almost 1 billion tonnes of tailings over 31 years, required a scheme comprising a 39.5m high and 1000m long downstream raise to the Main Embankment, in four separate stages. Stage IIB and IIC, for a total height of about 20m, have been completed. Stability analyses showed that the seismic stability of a raised clay core was not sufficient, due to the geometry of the raising. Furthermore, no suitable clay based materials were available at site. ATC Williams, designers of the dam raising, considered as alternative solutions an asphaltic core, an upstream bituminous membrane, and polymeric geomembranes. An upstream exposed PVC geomembrane facing (GFRD) was selected because of superior safety in respect to earthquake. ATC Williams deeemed he GFRD system would be the most stable, efficient and buildable arrangement. The finishing layer of the embankment is made with extruded porous concrete curbs. The face anchorage for the SIBELON® geocomposite was the Carpi patented method with SIBELON® anchor strips. As the embankment is being raised, the SIBELON® strips are nailed to the curbs and then permanently anchored by the fill compacted against the curbs. Overlapping SIBELON® strips are joined by heat-seaming.

Construction of extruded porous concrete curbs (left) with an extruding machine built in Iran. Heat-seaming of overlapping SIBELON® anchor strips one upon the other (right).

The SIBELON® strips heat-seamed at the overlapping form continuous anchor lines. The SIBELON ® geocomposite liner sheets are then deployed from the crest, after having been secured at top by a stainless steel batten strip on a conventional concrete curb.


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After cleaning the SIBELON ® anchor lines (left), the SIBELON ® geocomposite sheets are temporarily anchored at the crest of Stage IIB, and then unrolled down the slope (right).

The SIBELON® geocomposite sheets are heat-seamed to the SIBELON® anchor SIBELON® geocomposite sheets are watertight heat-seamed at overlappings.

strips. Adjoining

The SIBELON® geocomposite sheet is heat-seamed to the SIBELON ® anchor lines (left). Adjoining SIBELON ® sheets are watertight heat-seamed to form one continuous watertight facing (right).

The SIBELON® geocomposite used for the anchor strips and for the liner is SIBELON® CNT 4400, consisting of a 3mm thick PVC geomembrane, heat-bonded during manufacturing to a 500g/m2 non-woven polypropylene geotextile. The bottom seal of Stage IIB was made by embedding the SIBELON® geocomposite in a trench excavated in the existing clay core and then backfilling with clay. The bottom perimeter seal at the concrete plinth of the abutments is mechanical, of the so-called tie-down type. In tie-down seal, watertightness against water in pressure is attained by compressing the SIBELON ® geocomposite unto the concrete of the plinth with flat stainless steel batten strips secured by stainless steel anchor rods embedded in chemical phials at regular spacing. Regularising resing, rubber gaskets, stainless steel batten strips and splice plates achieve even adequate compression necessary for watertightness.


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Mettere foto trench

CARPI TECH

Stainless steel batten stri E ox resin SIBELON® eocom osite Rubber gasket

Bottom perimeter seal embedded in a trench excavated in the clay core of the existing main dam (left) and tie-down perimeter seal on he concrete plinth at abutments (right).

The intermediate seal between Stage IIB and Stage IIC is made by watertight joining the the upper geocomposite on the lower geocomposite and covering the seam with a horizontal SIBELON® geomembrane cover strip. The perimeter seal at top of Stage IIC is made by embedding the geocomposite in a trench then ballasted with a conventional concrete beam.

Intermediate seal between Stage IIB and Stage IIC (left) and top perimeter seal at Stage IIC (right).

Stage IIB and Staged IIC raisings reached 20m of height. Total surface was 38,500m 2. Installation of the waterproofing system, after completion of the curbs, took 14 weeks in total. The designers statement on the advantages of the GFRD has been: “The extruded curbs have proven to be an effective construction method, whilst the anchor strip installation became a simple, routine process…. The installation was fast…. The overall construction period was also significantly reduced…… Impoundment of water against the toe of raised embankment has recently commenced, and seepage measurements downstream of the embankment have not changed from their steady-state levels. It is concluded that the geocomposite faced rockfill approach is a viable, effective means of tailings dam construction …. where natural materials are either not available, or are unable to be used from a technical perspective”. 3.2

Upper part of Runcu GFRD, Romania 2014

Runcu is a 91m high and 324m long rockfill dam under construction in Romania, which will be used for water supply and irrigation. The original design was for a CFRD, with a homogeneous rockfill on which are placed a Zone 2 (5 to 250mm) layer, followed by a Zone 1 (5 to 90mm) layer, both 5m thick, and by a 0.2m thick layer of sand and gravel. Construction of the dam body and of concrete slabs was planned to be made in three stages, to allow partial operation of the dam while construction was in progress. The first phase was 150210_GFRDCaseHistories

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to be 36m high, the second phase 29m high, and the third phase 26m high. The inclination of the upstream face is 1V:1.4H. Constructing the various layers under the concrete slabs proved to be time consuming. Construction of the reinforced concrete face slabs and embedded lines of waterstops is a complex, trick and time consuming task. The high costs involved with a CFRD designwas an additional issue. When the first phase of the embankment had already been completed, the design was modified from a CFRD to a GFRD. Since when the design was changed more than one third of the dam had already been constructed, the design of the GFRD had to adapt to the existing situation. From about 5m above the completed part up to crest, for a total height of 50m, the three granular layers have been eliminated and the face is formed by extruded porous concrete curbs embedding SIBELON® anchor strips, to construct the same GFRD as in the Sar Cheshmeh project. The waterproofing SIBELON® CNT geocomposite is 3.5mm thick for the bottom and intermediate parts, and 2.5mm thick in the top part. Up to date, the construction of the curbs embedding the SIBELON® anchor strips is being carried out the intermediate and upper phases.

Extrusion of curbs, placement of PVC anchor strips and general view of the intermediate part of the dam.

For the 41m of the bottom part, since the curbs are not present, the system with SIBELON® anchor strips embedded in trenches has been adopted. See chapter 4 “GFRD projects with SIBELON® anchor strips embedded in trenches: case histories”. 3.3

Nam Ou VI, Lao PDR, first stage completed in November 2014, whole completion in December 2015

Nam Ou VI Hydropower Project is under construction in the the Fengshali Province of the Lao People Democratic Republic. The scheme, which will have a total installed capacity of 180 MW, is owned by Sinohydro Resources Limited. Designer is Hydrochina Kunming Engineering Corporation and Main Contractor is Sinohydro Corporation Engineering Bureau 15. Financing of the $2 billion project is reportedly being provided by the China Development Bank. Given the enormity of the project, China’s state-owned Sinohydro Corporation has divided the ten-year construction period of the HEPP into two stages. The scheme includes a 88 m high rockfill dam, which when completed will be the highest GFRD in Lao PDR. Nam Ou VI rockfill dam has been designed as a Geomembrane Face Rockfill Dam (GFRD). Reasons for choosing a geomembrane facing instead of another type of facing is that 90 cm settlements are expected to occur at the end of construction and during service life, and that the exposed geomembrane facing is safer, has a lower cost and a shorter construction period than a concrete facing. The dam is 362m long, has upstream slope inclination 1V:1.6H, and total upstream face surface of 38,000m2.


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Nam Ou VI (Lao PDR): artist’s impression of the HEPP , and excavation and construction of plinth.

Sinohydro Corporation is the largest hydropower construction company in the world, with a 50% share of the international hydropower market, which consists of a 65% share of hydropower projects within China. The geomembrane system conceived in the original tender design, issued by Sinohydro in autumn 2013, consisted of a 2mm thick High Density Polyethylene (HDPE), or Low Linear Density Polyethylene (LLDPE) geomembrane, sandwiched between two layers of 500 g/m 2 non-woven needle-punched polyester geotextile. The geomembrane was to be placed on a granular cushion layer, in turn placed over a granular transition layer, and was designed to be covered either by precast concrete slabs or by shotcrete. Function of the cover layer was to ballast the geomembrane, and to shield it from UV rays, preventing in this way its aging. A backfill wedge was to be placed at the upstream toe. Carpi, with the help of Dr. JP Giroud, one of the most renowned experts in geosynthetics, proved to Sinohydro that neither HDPE geomembranes nor LLDPE geomembranes are suitable for applications in dams, especially with characteristics as Nam Ou VI dam. On the contrary, SIBELON ® PVC geomembranes fulfil all requirements requested to the system: watertightness, capability to maintain its watertightness also in conditions of large elongations caused by large deformations in the dam body, and guaranteed durability for the whole design service life of the dam. Sinohydro cancelled the tender in which Chinese companies, who offered much cheaper solutions, were recognized to be not fit to provide a reliable long lasting solution for such a project, and awarded the contract to Carpi. After award of the project to Carpi, the decision of renouncing to the cover layer was also taken, as the cover layer was not considered anymore necessary, neither for fastening the geomembrane system, nor for its durability. This involved further cost savings. The dam became a Geomembrane Facing Rockfill Dam (GFRD). The GFRD consists of a Carpi SIBELON ® CNT geocomposite totally exposed, installed on one layer of extruded porous concrete curbs, and anchored with the same system described in the previous case history.

Nam Ou VI rockfill dam (Lao PDR). Left: construction of the porous concrete extruded curbs. Middle: placement of SIBELON® CNT geocomposite anchor strips in the curbs. Right: construction of the embankment+anchor strips in August 2014.


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The exposed geocomposite that is the only element providing watertightness to the dam is SIBELON® CNT 5350, consisting of a 3.5mm thick PVC geomembrane laminated during fabrication to an 800g/m2 nonwoven geotextile. Installation of the Carpi geomembrane system at Nam Ou VI dam is staged. In the first stage, completed in 2014, the dam has reached a height of 48m.

Nam Ou VI rockfill dam (Lao PDR). The figure at left shows SIBELON ® CNT 5350 geocomposite under placement and fastening to the SIBELON® CNT geocomposite strips embedded in the curbs. The figure at right shows the Carpi geomembrane system installed in the first stage, corresponding to approximately 48m of the total height. This figure was taken in November 2014. Carpi shall start the second stage installation after construction of the embankment is completed.

Expected date for start of the second stage, for further 40m, is April 2015, and commissioning of the dam is due by January 2016.

Nam Ou VI rockfill dam (Lao PDR) – November 2014: end of first phase of installation. 3.4

Tailings dam, GFRD, Peru, Stage 1A completed in 2014

A mine project, whose name cannot be disclosed due to a confidentiality agreement with the Owner, is under construction in Peru. The open-pit resource will process at a production rate of approximately 50 million tonnes per annum. Tailings from the mine processing plant will be pumped to a Tailings Storage Dam adjacent to the concentrator plant. The dam will be located within a broad valley bounded by the concentrator, the main waste dump and the open-cut pit. For mine start-up purposes, the dam will be the primary water storage for the commissioning of the concentrator plant. The dam will continue to be utilised as water storage throughout the operating life of the mine. Since the dam will need to be a water retaining embankment, it was designed as a rockfill dam with an upstream exposed geomembrane sealing system (GFRD). The GFRD option was selected due to the lack of suitable impermeable material for constructing a clay core dam.


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The dam was initially designed with a slope of 1V : 3H to allow the installation of an exposed LLDPE geomembrane. During the review of the design, ATC Williams found that the design was not providing enough factor of safety for the geomembrane anchorage. Further analysis, corroborated by studies of Dr. JP Giroud, demonstrated that a SIBELON® geocomposite would have been a safer option, allowing to increase the steepness of the slope to 1V : 1.7 H, which result in an expected saving of some 50 million USD. The exposed geocomposite that is the only element providing watertightness to the dam is SIBELON ® CNT 3100, consisting of a 2.0mm thick PVC geomembrane laminated during fabrication to a 500g/m2 nonwoven geotextile. The SIBELON® geocomposite is fastened with the SIBELON® anchor strips system embedded in extruded porous concrete curbs, according to the same GFRD system described in the previous case histories. The tailings embankment will be constructed in a number of stages using the downstream raising approach. The first stage has been divided into two parts (Stage 1A and Stage 1B): - Stage 1A, which has an approximate height of 45m, and has the primary purpose of establishing a startup water storage for the mine - Stage 1B will raise the embankment to a maximum height of 100m, in order to provide tailings storage for the first year of operations. The Tailings Retaining Embankment will then be progressively raised in stages to a final maximum height of approximately 230m.

Tailings dam (Peru). At left the embankment and extruded curbs under construction, at right a close view of the anchorage lines by SIBELON ® anchor strips embedded in the curbs. Right: Stage 1A of the dam under construction in October 2014.

Tailings dam (Peru). At left stage 1A of the dam body completed, embedding the SIBELON ® anchor strips in the curbs, at right the SIBELON® geocomposite under installation SIBELON ®on the anchor strips.

In year 2014, Stage 1A has been completed. The exposed geomembrane system has been installed from


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elevation 3932m a.s.l. to elevation 3974m a.s.l.

Tailings dam (Peru). At left the geomembrane system under installaiton at the right abutment, at right waterproofing of Stage 1A nearing completion in December 2014. 3.5

GFRD project approved and to be constructed: Dugald River dam, Australia

Dugarld River dam is part of the Dugald River Project Tailing Storage Facility. The dam will contain all water released from the tailings and storm water runoff from the 335 hectares catchment, and potentially provide storage for underground mine dewatering and additional mine site water inputs during high wet season rainfall periods. The dam, a rockfill embankment with a concrete upstream toe plinth, has been designed by ATC Williams following the excellent behaviour of Sar Cheshmeh dam raising, and the successful experience of Stage 1A of the tailings dam in Peru. The upstream face will be formed with extruded porous concrete curbs embedding the SIBELON® anchor strips, to which the SIBELON® geocomposite liner will be fastened. Identical system as for Sar Cheshmeh. The dam will be 40m high and 225m long, with upstream face inclination 1 V:1.5H.

Dugald River dam. 3.6

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Advantages of the system with SIBELON anchor strips on extruded curbs

This system combines the advantages of the extruded porous concrete curbs with the advantages of the Carpi exposed system.


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Thanks to the containment produced by the curbs, segregation of the transition material is reduced and its placement is more economical. The curbs can be placed on the drainage/filtration layer or directly on the fill material, and allow constructing steeper embankmentes with consequent reduction of the fill volume. The curbs do not require stabilisation of the facing, less people need to work on the face slope, construction equipment is simplified. The curbs can be built simultaneously to construction of the fill, have uniform characteristics, construct over the whole upstream face a base layer stable, not erodible nor affected by heavy rains, on which workers can walk without causing any displacement. Construction times of this stable and regular base layer are much shorter than with traditional multi-layered granular systems. The Carpi system in association with the extruded porous concrete curbs method permits to complete much more quickly the installation of the waterproofing system as compared to a CFRD installed on curbs. Placement of the geomembrane on the curbs does not need subgrade preparation. No need of complex installation of embedded waterstops, whose effectiveness and performance depend on high experience of the main contractor and on skill of crews. Installation of the geocomposite sealing system can be made in stages, while construction of the dam proceeds. This will allow protecting the dam if floods occur during construction. And most important, when in operation the deformable and elastic watertight facing will be able to sustain settlements that would cause cracking of face slabs and possible failure of the waterstops, with consequent need to dewater the dam, to perform time consuming and costly repair, and possibly go through long disputes on liabilities. In summary, technical and practical aspects related to construction of the base layer with porous concrete extruded curbs in combination with Carpi geomembrane system result in a technically reliable and very economical solution. 4

4.1

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GFRD PROJECTS WITH SIBELON ANCHOR STRIPS EMBEDDED IN TRENCHES: CASE HISTORIES Kouhrang headpond GFRD, Iran 2004

Kohrang headpond is part of the 13.5 Mw installed capacity Kohrang hydropower plant in Iran. The dams forming the headpond are 16.5m m high and 460m long. The dams were originally conceived as rockfill dams with concrete face or with asphalt concrete face. In subsequent studies, due to the high risk of settlements arising from non-uniformity of soil layers in the foundations, and to the seismicity of the site, concerns arose about cracks forming in the concrete lining as consequence of settlements, and about durability of the concrete facing. The concrete and asphalt concrete options were eliminated. Three alternatives were retained: rockfill dams with a clay core, homogenous impervious embankments, and homogenous embankments with a geomembrane liner. The three variants were fully designed and compared. The designers selected the Carpi upstream totally exposed PVC geomembrane system based on - the almost zero permeability of the geomembrane - its capability of maintaining watertightness even in the case of large settlements of the embankment - its capability of maintaining watertightness at connections to concrete appurtenances under large foreseen differential settlements - its durability of the geomembrane in extremely cold (-37°C) and hot (>40°C) temperatures - the overall lower cost, the higher speed of construction, and the simplification of construction works and quality control that the geomembrane system could provide. The embankments and bottom of the headpond are formed by soil. Parallel trenches were excavated in this base layer, at spacing calculated to resist wind uplift. A SIBELON® geocomposite anchor strip was placed in each trench and then ballasted by porous concrete.


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After construction of the fill has been completed, anchor trenches were excavated and formworks placed inside the trenches. Then, the SIBELON® geocomposite anchor strips were put inside the formworks, and porous concrete was cast on them, to provide permanent anchorage of the strips.

The SIBELON® anchor strip can be seen exiting from the right side of the trenches, after ballsting by po rous concrete.

After demolding, all spaces at the sides of the anchor trenches are filled and the dam face is compacted.

After placement of the SIBELON® anchor strips and backfilling of the trenches with draining material, the SIBELON® geocomposite sheets were temporarily anchored at crest and then deployed over the slopes. The SIBELON® sheets were heat-seamed to the anchor strips. Adjoining SIBELON® sheets were watertight heat-seamed to form one continuous watertight facing. The following photos illustrate the process.

SIBELON® anchor strip and SIBELON ® sheets unrolled from the crest.


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Heat-seaming a SIBELON ® geocomposite sheet to a SIBELON ® anchor strip, and watertight heat-seaming of adjacent SIBELON® geocomposite sheets.

The dams and bottom were lined with the same system.

Peripheral anchorage at crest and bottom of slopes was made in anchor trenches backfilled with concrete. In total, 16,500m2 were waterproofed in 35 days.

The settlements that had been foreseen during the design phase occurred after impounding; temperature went down to 37ºC below zero, with heavy snow and ice formation. As a consequence of the settlements, some fissures opened at the contact between the fill dam body and the concrete appurtenances. No damage to the exposed geomembrane.


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The owner reported that “Because of the use of the geomembrane solution, the following benefits have been gained by the owner: • A saving of 60 per cent was achieved in the volume of fill material. • Construction was faster and easier. • The volume of impounded water compared with the original design was increased by 25 per cent, which

creates more energy generating capability. • Construction costs for the head pond could be decreased by 50 per cent.” 4.2

Murdhari GFRD, Albania 2013

Murdhari dam, owned by Hydroenergy, is located on Murdhari river, 28 km far from the Capital city of Tirana. The 36m high rockfill dam that was originally designed with an asphalt core. When construction had already started, the owner seeked an alternative solution to the original design, to make construction safer, faster, easier to build and less expensive. The selected solution consists in a SIBELON® geocomposite system anchored to the upstream face of the dam along anchor lines parallel to the slope, to construct a GFRD. Construction of the fill was already ongoing. The main contractor, not familiar with extruded porous concrete curbs placement, proposed to form the finishing layer with porous concrete slabs, leaving a gap between adjacent slabs, to form anchor trenches for the SIBELON® anchor strips. Carpi adapted its design to this construction method: starting from the bottom and proceeding upwards, the gap was filled by superimposed porous concrete blocks. After the first block was completed, a SIBELON® anchor strip was placed on it and permanently anchored by another porous concrete block placed on top, and so on up to the crest.

Forming the face porous concrete slabs, and placing the SIBELON ® anchor strips on the porous concrete blocks inside the gaps.

In practice, instead of placing porous concrete by curb extruder, porous concrete is constructed in superimposed small blocks. Continuous parallel SIBELON® anchor lines, like in the method with extruded porous concrete curbs, form the face anchorage system. The SIBELON® geocomposite sheets are then deployed and heat-seamed to the SIBELON® anchor lines.


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The SIBELON® anchor lines and the SIBELON ® geocomposite unrolled down the upstream face.

The SIBELON® CNT 5050 geocomposite consists of a 3.5mm thick PVC geomembrane thermally bonded during manufacturing to a 500g/m2 nonwoven geotextile. Watertight perimeter seals have been installed at all submerged peripheries (toe wall and around the intake tower) while the seal at crest is of the tie-down type, and watertight against rain, snowmelt and waves only. Carpi crews were on site on September 16th 2013 and the works were completed on October 19th 2013, for a total of 6,770m2 SIBELON® geocomposite installed.

View of the upstream face after installation of the Carpi geomembrane system. 4.3

Lower part of Runcu GFRD, Romania, 2014

As mentioned in sub-chapter 3.2 “Upper part of Runcu GFRD, Romania 2014 ”, when the design was changed to a GFRD, the bottom part of the dam had already been constructed according to the original design with zoned granular material. Also in this dam the design of the GFRD therefore had to adapt to the existing situation. The SIBELON® anchor strips are embedded in trenches excavated in the existing facing. To provide a draining base layer similar to the curbs of the upper parts of the dam, 20 cm thick layer of porous concrete is cast on the granular fill, with the exception of the gap for the anchor trenches.


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Excavation of trenches, and pouring of porous concrete base layer.

The SIBELON® anchor strips are placed in the trenches, and ballasted by unreinforced concrete beams cast in situ.

The SIBELON® anchor strip embedded in one of the trenches, with two free flaps at the edges. Starting from bottom upwards, a concrete beam is cast in the trench, to provide the ballast permanentls fastening the SIBELON ® anchor strips to the dam face.

The two free flaps of each SIBELON® anchor strips will be heat-seamed one upon the other so as to completely wrap the beam. The waterproofing SIBELON®geocomposite will then be heat-seamed to the SIBELON® geocomposite wrapping the beams.


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The perimeter seal at plinth and at crest is of the mechanical type, with stainless steel batten strips fastened to the concrete with chemical anchors. 4.4

GFRD at the 18 Water Saving Basins of the Panama Canal Expansion project, 2014 and 2015

A critical part of the extension of the new Panama Canal, which will allow doubling the ship traffic, are the 18 water saving basins, which will allow saving some 60 % of the total volume of water when operating the locks. They had been originally designed with a PVC geomembrane covered by some 20cm of concrete. The final design has been changed to an exposed Carpi SIBELON® CNT 4400 geocomposite, consisting of a 3mm PVC geomembrane heat-bonded during manufacturing to 500g/m2 geotextile. The water head is 6m and the total surface some 600,000m2. Avoiding the concrete layer allows for a safer construction, deleting the risk of damaging the geomembrane during the concrete placement, and also for a cost reduction of more than 20,000,000 USD. The change to an exposed thick SIBELON® geocomposite has been adopted because of the Durability Report on Carpi geomembrane issued by the most worldwide renowned geosynthetics experts and laboratories, which announces an expected durability exceeding 100 years for the exposed Carpi SIBELON® geomembrane.

Expansion Project. In total, some 600,000m 2 of exposed Carpi SIBELON ® geomembrane to line the 9 water saving basins on the Atlantic side, pictured, and the 9 basins on the Pacific side. Artist’s view of part of the Panama Canal

The anchorage system for the SIBELON® geocomposite has been designed in function of the type of subgrade found on the slopes and bottom at the Pacific and Atlantic sides. Where possible, the system with anchor trenches has been adopted. Elsewhere, deep anchors.

Panama Canal Expansion Project. Placement of SIBELON ® geocomposite and filling of anchor trench on slope.


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Panama Canal Expansion Project.

Panama Canal Expansion Project. Aerial view of Atlantic side. 4.5

GFRD project approved and to be constructed: Bulga, Australia

Glencore Bulga Coal Management Pty Ltd, owner of Bulga Coal Mine, in Australia, has been investigating the option to expand and optimise the existing Bulga Coal Mine. Studies for the Bulga Optimisation Project have identified a potential surplus of mine water and the resultant need for a 2 Giga Liters water dam within a broad, natural valley to the north of the current Bulga operations (i.e. the Northern Water Dam). ATC Williams is the designer of the Bulga Northern Water Dam. Purpose of the dam is to provide water storage for dewatering of open cut coal mining pits and the replacement of other water storages on the mine site that will, in the future, be removed due to pit expansion. The dam will be equipped with a controlled discharge system and during permitted periods will discharge water into Loders Creek, which feeds into the Hunter River. As part of the Hunter River Salinity Trading Scheme, controlled releases of water with higher than normal salinity levels are only allowed during certain times (specified by the Department of Environment and Conservation NSW). A further requirement is to separate ‘clean’ and ‘dirty’ water, by diverting run-off water from the surrounding catchment around the dam into Loders Creek. The diversion of the run-off water 150210_GFRDCaseHistories

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reduces the overall required capacity of the dam, thereby reducing the risk to the downstream environment. The controlled outlet structure is a gravity system able to cater for peak flows in excess of 500 Million Liters per day. The controlled outlet flow passes through a concrete energy dissipation structure before being directed to a stilling basin. All ‘dirty’ water will be passed through an overflow weir prior to being released into Loders Creek. For the reasons of construction costs and availability of materials, the Designers considered two embankment configuration options for the Northern Water Dam Main Embankment. The two options are: - Modified Homogenous Earthfill Option – zoned earthfill embankment comprising clay, limestabilised clay, sand filters and extremely to highly weathered rock. - Geomembrane Option – zoned earthfill embankment fitted with a waterproofing geomembrane sealing system on the upstream face, to construct a GFRD. In order to determine the preferred embankment configuration, conceptual designs were completed and preliminary stability analyses performed. Comparative costings were then developed, based on an assessment of materials requirements and sources, quantities, and previous budget rates for civil works items submitted by specialist construction contractors. On the basis of capital costs, construction efficiency, materials availability and serviceability, the Designers selected the GFRD option as the preferred configuration for the dam.

Bulga Northern Water Dam. Main Embankment. Typical cross section.

The general embankment design comprises an exposed PVC geocomposite anchored on the upstream face of the embankment to a base layer of Zone 1A lime-stabilised clay earthfill. Separating the geocomposite from the Zone 1A will be a triaxial drainage net, which will ensure that in the unlikely event of a concentrated leak, seepage water will be safely drained away to avoid erosion of the clay base layer. The triaxial drainage net will be connected to slotted collector pipes at the upstream toe, which will in turn be connected to an outlet pipe discharging into a sump downstream of the embankment. The remainder, and bulk of the embankment, will consist of conditioned and compacted Zone 3A and 3B extremely weathered (EW) and highly weathered (HW) sandstone earthfill. These zones provide strength and stability to the structure and support the upstream SIBELON® geocomposite. The zones will differ on the basis of maximum allowable particle size, placed layer thickness and the compaction requirements. The watertight geocomposite is SIBELON® CNT 4400, consisting of a 3mm thick PVC geomembrane heat bonded during manufacturing to a 500g/m2 non-woven needle-punched geotextile, having the function of anti-puncturing layer. The anchorage to the dam face consists of SIBELON® geocomposite strips placed in trenches that are excavated in the base layer and backfilled with draining material (porous concrete or granular material), similar rto the case histories previously discussed. The SIBELON ® geocomposite strips embedded in the trenches form continuous anchorage lines, to which the overlapping SIBELON® geocomposite sheets are 150210_GFRDCaseHistories

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heat-seamed. The following figure shows a cross section of the embankment with a detail of this anchorage system.

Bulga Northern Water Dam. Main Embankment. Typical cross section of an anchorage trench excavated in the base layer. 4.6

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Advantages of the system with SIBELON anchor strips embedded in trenches

This system allows constructing a GFRD with practically any type of base layer, when either the design does not envisage an extruded curbs facing, or construction of the facing has already advanced with another system. The system is highly adaptable to site-specific conditions and constraints, but is more time consuming than the system with the extruded curbs. The choice between one system and the other will be driven by factors like availability and price of concrete, availability and price of labour, experience and confidence of the main contractor with traditional methods or with curbs extruders. 4.7

A pioneer project: Alento cofferdam, Italy 1988

Alento is a 21m high cofferdam in Italy. The cofferdam was constructed with random fill, embedding SIBELON® geomembrane patches placed at approximately 4m spacing, every 4m of height of the dam. Such patches constituted the anchorage system for the SIBELON® geocomposite. In practice, instead of continuous SIBELON® anchor lines, SIBELON® patches providing anchorage at points. The SIBELON® geocomposite was anchored to the dam body by heat-welding it unto the SIBELON® patches. Installation of the waterproofing system was completed in 1988. Due to delay in construction of the main dam, the exposed geocomposite system remained in service 10 years, withstanding two major floods.

Alento, Italy 1988: the SIBELON® geocomposite is anchored by welding over the protruding part of SIBELON ® patches embedded in the fill.


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Geomembrane Facing Rockfill Dams – GFRDs 5

CARPI TECH

GFRD PROJECTS WITH DEEP EARTH/GROUTED ANCHORS: CASE HISTORIES

Anchorage by deep earth anchors is used when the base layer for the geomembrane system is made of granular materials. When the facing is completed, the deep anchors are driven into the embankment and fastened to it. The SIBELON® geocomposite is then punched on the anchors and watertightness is restored where the SIBELON® geocomposite has been punched, with appropriate devices. Different types of deep anchors are available and described in the case histories that follow. 5.1

Vaité earthfill dam, French Polynesia 2011

Vaité is a 23m high earthfill dam in the island of Tahiti in French Polynesia, owned by Electricité de Tahiti / Marama Nui. The upstream face has an inclination of 1V:1.84H. A 1mm thick PVC geomembrane installed on an anti-puncture geotextile in 1987 provided the waterproofing system. In total 3,800m2 at the upstream face, about 2,040m2 on the bottom of the reservoir, fabout 2,500m2 at the right abutment, and about 690m2 at the left abutment. As the old geomembrane was no more fully performing, in 2010 the owner and its consultants Tractebel Engineering France Coyne et Bellier decided to remove the geomembrane and replace it with a fully exposed SIBELON® geocomposite. The requirements for the anchorage of the new geocomposite were: in the top 1/5 of the dam resist wind uplift of 204km/h ("hurricane conditions") with a Factor of Safety FS ≈2, and in the

remaining 4/5 of the dam resist wind uplift not inferior to 100km/h. The new liner SIBELON® CNT 3750, a 2.5mm thick PVC geomembrane laminated to a 500g/m2 anti puncture geotextile, was installed directly on the fill after removal of the old geomembrane and geotextile. The anchorage system for the SIBELON® geocomposite at the upstream face of the dam and at the right abutment is exposed and anchored with deep earth anchores of the duckbill type, and covered at the bottom of the reservoir. The left abutment was shotcreted. The deep earth anchors, Duckbill type, consist of a stainless steel bar or wire, of a rotating Duckbill and of a tendon, which are driven into the ground. When the anchor is fully inserted, an upward pull on the tendon rotates the Duckbill into a perpendicular "anchor lock" position in the soil. The results of real scale field testing carried out prior to final design showed that the deep anchors could soundly anchor the geocomposite.

The Duckbill anchor in before and after rotation.


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The deep anchors were installed in a regular pattern of vertical and horizontal spacing, in function of the required resistance to wind uplift.

Placement of SIBELON ® geocomposite on the earthfill, and preparation of the Duckbill anchor.

The duckbill anchors are driven into the earthfill. At right, detail of the stainless steel anchor rods and protection plates before being cut flush and waterproofed.

Perimeter seals are on the tie-down type concrete (new concrete perimeter beam at the left and right sides of the dam and at bottom, spillway and crest of the dam, at new concrete structure for the outlet and intake conduits, and at new concrete perimeter beam at the upstream end of the lined area). At the upstream bottom edge the perimeter seal was made by anchorage in a 2m deep peripheral trench filled with backfill. The watertight connection between the various areas was made by overlapping and watertight heat-seaming the SIBELON® geocomposites.

At bottom, the SIBELON® geocomposite (grey) has been covered by a protection geotextile (white), and by alluvial fill and cement stabilised gravel. At right, view of the dam, right abutment and bottom.


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Vaité, French Polynesia.The impounded reservoir. 5.2

Filiatrinos, Greece, 2015

Filiatrinos is a 55m high dam under construction in Greece. The owner is the Ministry of Rural Development and Food, the designer is the Greek firm “Hydrosystima”. The dam is being constructed as a hardfill dam.

The final original design of the dam foresaw reinforced concrete slabs as upstream waterproofing system.

Filiatrinos hardfill dam under construction.

The dam is symmetrical, inclination of slopes: 1V: 08H, with a perimeter plinth at upstream toe, and backfill from upstream toe to elevation 185m a.s.l. Intrakat, the Main Contractor who is building the dam, to investigate the possibility of improving the characteristics of the dam, hired an independent Consultant to make an assessment of a new design replacing the upstream concrete slabs that have not yet been cast (from elevation 170m up to crest, about 10,200 m2) with an exposed geomembrane system. The assessment by the independent consultant concluded that “Replacing the upstream concrete slab with a

layered sealing system of geotextiles and geomembrane on the dam upstream face, is technically fe asible and improves the safety and behaviour of the dam, under the expected loading conditions. ” The revised design is that of an exposed geomembrane system, placed over the hardfill and anchored with deep anchors, accordign to the same concept adopted at Vaité. The new waterproofing system had to be adapted to the existing situation, i.e. a hardfill dam almost completed.


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Filiatrinos embankment on November 21, 2014.

Some features of the dam show inadequate construction procedures. The embedement of the drainage pipes is not as specified on the entire dam, at some places the pipes are either not embedded or protruding from the hardfill. The strength and stability of the subgrade is not constant over the face. The reduced compaction of hardfill close to the upstream face of the dam, in conjunction with low cement content, results at some locations in the limited adherence of aggregates of the embankment.

Filiatrinos : discontinuous drainage pipes embedment, accumulation of detached gravel near the plinth.

The application of a geomembranesystem, which is a relatively simple and quick task if selected as a solution at the initial planning stage of the dam, when selected 'retrospectively' as a result of amendments to the design of an existing project (as in this case the Filiatrinos dam), entails some issues to be addressed. The tensile properties of the SIBELON® geocomposite system however allow adapting to porblematic situations and minimise preparatory works. The ondulations of the surface due to the hard fill excess material will be regularised manually, by local scraping. To address the possible detachment of aggregates, application of shotcrete and implementation of asphalt emulsions were discussed. The two solutions were discarded and eventually the option has been selected of using a strong geotextile layer, fixed to the body of the dam with anchors. The drainage pipes not adequately embedded will be cut flus and filled with suitable permeable material, in the aim both to reduce drastically the deformability of the pipes, and to avoid deviating from their basic function which is to drain. The waterproofing liner is SIBELON® CNT 4400, a geocomposite consisting of a 3.0mm thick PVCgeomembrane, extruded in homogeneous mass by a flat die, formulated to be UV resistant, and heat bonded during fabrication to a 500 g/m2 anti-puncture geotextile. The face anchorage system ise designed in function of the type of subgrade, and of the load (wind, water head) acting on the geocomposite. At Filiatrinos, 2 zones have been identified 150210_GFRDCaseHistories

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-

From crest elevation + 214.80 to elevation + 185 where the subgrade is more resistant and stable, the geocomposite can be exposed to wind & varying water level. Systematic face anchorage is foreseen, by some 400 deep anchors, with different spacing. A system similar to what adopted at Vaité dam - From elevation + 185 to plinth: the geocomposite in service will be mostly underwater (lower operation level 180.00). According to the current, revised design the area below el. 185 will be covered by backfill, as it was in the original design with concrete slabs. The face anchorage therefore will be provided by the ballasting action of water and backfill. 5.3

Ambarau, Democratic Republic of Congo, to be constructed

Ambarau hydropower dam is under construction in the Democratic Republic of Congo. The owner is Rangold, the designer is the South African firm ARQ. The dam is currently being constructed as a hardfill dam with reinforced concrete slabs as upstream facing element. The dam is 21m high from foundation, Symmetrical cross section with slopes 1V: 75H. ARQ, the engineering company who is designing the dam, intends to replace the upstream concrete slabs foreseen in the current design with an exposed geomembrane system. The exposed Carpi PVC geomembrane system is intended to function as waterproofing and protection system of the hardfill.

Ambarau hardfill dam location.

The waterproofing geocomposite is SIBELON® CNT 4400, consisting of a 3.0mm thick PVCgeomembrane, extruded in homogeneous mass by a flat die, formulated to be UV resistant, and heat-bonded during fabrication to a 500 g/m2 anti-puncture geotextile. The geocomposite is to be securely fastened to the dam face so to resist uplift by back-pressures, wind and waves, by anchorage lines obtained by deep anchors placed in a regular pattern. 5.4

Deep grouted anchors at canals’ embankments

In canals formed by embankments where the original watertight liner has been heavily deteriorated or whased out, the new exposed SIBELON® geocomposite liner is generally anchored against dynamic load of water by stainless steel anchorage profiles. The anchor bars for the profiles, when the subgrade is heavily deteriorated, is made by deep grouted anchors. This system has been adopted at Laufnitzdorf hydropower canal (Austria 2000), originally lined with concrete that had practically been washed out, at Mittlere Isar-Strogenbauwerk canal (Germany 2000), and at Pernegg canal (Austria 2000).


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Deep grouted anchors at Laufnitzdorf (top and bottom row at left) and Isar and Pernegg canals (bottom row at middle and right). 5.5

Advantages of the system with deep anchors

Experience at Vaité dam and at the canals in Austria and Germany has shown that the anchorage system with deep anchors can be installed in any kind of subgrade, quickly and without any inconvenience. Application of the system to new embankment dams will allow constructing very quickly and at low cost impervious dams consisting of compacted fill providing stability, and with a flexible upstream liner providing imperviousness, and capable of accommodating settlements and differential movements exceeding by f ar any possible anticipated value.


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Geomembrane Facing Rockfill Dams – GFRDs 6 6.1

CARPI TECH

PROJECTS WITH UPSTREAM COVERED GEOMEMBRANE: CASE HISTORIES Bovilla, Albania 1996

Bovilla is a 91m high dam located in a narrow gorge, in a seismic region of Albania. Conceived originally for irrigation purposes, it was subsequently designed to meet also the increasing potable water supply demand. The original design selected a CFRD, 1V:1.6H slope, 0.5m thick reinforced facing slabs over a grid of vertical and horizontal reinforced concrete beams. The reinforcing of the concrete elements, as well as the copper and PVC waterstops, was quite complex. Difficulties encountered while constructing the dam and compacting the fill raised concern for the final quality of the concrete facing, on the risk of cracking in the slabs, and on the need to reduce construction times of a project already behind schedule. It was deemed necessary to reconsider the design of the dam, in seek of a solution that would be less sensitive to differential displacements, cheaper and faster. In late 1994, when construction had already started, the CFRD design was modified to provide an upstream facing that could be constructed rapidly, and assure long term watertightness to the dam even in case of a seismic event. The new facing is a watertight geomembrane system consisting of a SIBELON® geocomposite (a 3mm thick PVC geomembrane heat-bonded to a 700 g/m2 geotextile). The geocomposite is placed over a 40cm thick transition layer made with gravel stabilised with low-cement mix to hold the gravel together, and is covered by cast-in-situ unreinforced concrete slabs, 0.2 to 0.3m maximum thickness. The perimeter mechanical anchorage of the geocomposite unto the concrete toe wall was designed to allow for sharp differential movements between the fill and the concrete wall. Placement of the waterproofing system started in May 1996 and was completed in September 1996. Net time required for placement of the geomembrane system was 30 days. The concrete cover was completed in November 1996. Switching from the original CFRD design to the SIBELON® system allowed to bring the project back to schedule. Saving on the expected total cost was 15%, saving of the geomembrane system compared to a concrete face was about 50%. In 2014, after 18 years of service, leakage at fully impounded reservoir of the 91m high dam is virtually zero.

Bovilla, Albania 1996. Design was modified during construction from a CFRD to a rockfill dam with upstream geocomposite covered by unreinforced concrete slabs 0.2 to 0.3m thick. Savings were 50 % of the original concrete face. From top left clockwise: the stabilised gravel on whih the SIBELON ® geocomposite was placed, the SIBELON ® sheets under placement, detail at plinth and the concrete slabs under placement. In 2014, after 18 years of service, total leaks at fully impounded reservoir of the 91m high dam are virtually zero.


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Geomembrane Facing Rockfill Dams – GFRDs 6.2

CARPI TECH

Jibiya, Nigeria 1997

Jibiya is a 21.20m high, 3,680m long earthfill dam that forms a reservoir used for irrigation. Completed in 1991, the dam has as sole water barrier an upstream PVC geocomposite consisting of a 2mm thick PVC geomembrane backed by a 400g/m2 geotectile. The inclination of the upstream slopes is 1V:3H. The geocomposite is covered by by cast-in-situ unreinforced 2x4m concrete slabs 8cm thick, placed on a 300 g/m2 geotextile.

Jibiya dam, Nigeria. The PVC geocomposite has been covered by a concrete layer, consisting of unreinforced slabs, 8 cm thick, cast in situ ( Courtesy P. Sembenelli ).

The dam was completed in 1991, installation of the PVC geocomposite was completed in 1990. In total, 165,000m2 installed. The reservoir has been operating successfully since then. 7

PROJECT WITH CENTRAL GEOMEMBRANE: GIBE III COFFERDAM

The third phase of the Gibe cascade, known as Gibe III, includes a 240m high RCC dam and an approximately 50m high rockfill cofferdam. The waterproofing system for the cofferdam is an impervious core, constructed concurrent with the cofferdam. The designer selected a geomembrane core, instead of a more traditional clay core, based on the following considerations : “A central geomembrane core was adopt ed because:

TIMING: it would allow complying the construction within the very short construction period SIMPLICITY: it would allow the realization of an embankment of homogeneous rockfill, with optimization in construction times and costs. NO CLAY: lack of availability in the zone of material suitable for an impervious-core. SAFETY: With such layout the impervious layer is embedded in the embankment, safer than any impermeable layer (BFRD or CFRD). Settlement is not a problem. Permeability tests done during construction provide a guarantee unusual for this kind of structure”. The impervious geomembrane core consists of a flexible 3.5mm thick PVC geomembrane, SIBELON® C 4550, sandwiched between two anti-puncture layers that protect it against possible damage by the construction materials. Two filter layers are placed at the upstream and downstream side of the geomembrane. The geomembrane has been installed from the clay cut-off up to the crest, in a zigzag pattern so as to follow the step by step the construction of the embankment and to be more flexible against possible settlements of the embankment. At bottom the SIBELON® geomembrane is embedded in the cut-off to provide watertight connection to the waterproofing of foundations.


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CARPI TECH C Cofferdam

2

sel B

Pre-Cofferdam

sel B

2

d/s toe

B/T

sel B

GW

0.5 3

~1.5

~1

1.5

W-CL

SW-CL

C

Cross section of Gibe III cofferdam.

When the first section of the cofferdam was completed, the first anti-puncture geotextile (white in the photo below) was placed on the sand layer, and the SIBELON® geomembrane (gray) was placed over it. Then construction of the second section started (at right) after the second anti-puncture geotextile had been placed over the SIBELON® geomembrane.

In the flat area at the crest of each section, the SIBELON® geomembrane lining the lower section overlaps the SIBELON® geomembrane lining the section above it, for a width of about 2m. In correspondence of this 2m wide overlapping area, the connection of the two SIBELON® geomembranes is made by means of a double track seam executed with automatic machine and tested with air in pressure. All construction steps are repeated at each section of the fill. In total, 15,213m2 of geomembrane installed.


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CARPI TECH

This solution presents many aspects that can give answer to some problems commonly encountered during design and construction of dams and cofferdams, like tight construction time schedules, lack of availability of impervious material (clay), complication of construction sequences and differential settlements for embankment realized with impervious core traditional materials, difficulties in managing settlements, difficulties in assuring proper protection and safety of the impervious layer

Gibe III cofferdam nearing completion, and impounded. 8

THE EXPOSED GEOMEMBRANE SYSTEM AS EXTERNAL WATERSTOP: ANGOSTURA CFRD, CHILE 20012

SIBELON® geocomposites are also adopted as external waterstops in CFRDs and RCC dams. An oustanding example is Angostura CFRD in Chile. Angostura is a CFRD owwned by Colbun S.A., 1,600m long, with a maximum height of 30m, and upstream inclination 1V: 1.5H. The concrete face consists of vertical slabs 15m wide and 0.40m thick, placed on a base layer of extruded curbs. The geological characteristics, and the topography and location, indicated that considerable differential deformations will occur at the dam. Three types of joints were identified at the dam: - The vertical compression joints between slabs, which shall accept deformations up to 5cm - The joint plinth/slabs in the lateral zones, which shall accept deformations up to ≈ 15cm in vertical and horizontal directions - The joint plinth/slabs in the central zone, which shall accept deformations up to ≈ 30cm in vertical and horizontal directions. Since the internal copper waterstops cannot resist such openings, the external waterstop had to be designed in order to be capable of accommodating the foreseen deformations and of maintaining watertightness at the peripheral and vertical joints in the worst-case conditions. Colbun selected among three different solutions Carpi external patented SIBELON® geocomposite waterstop. The waterstop developed for Angostura consists of a flexible SIBELON® geocomposite placed over a special high-tech isotropous geotextile, and watertight sealed at the periphery by a mechanical tie-down seal. The concept is that the SIBELON® layer will elongate over the deformed joint, and the geotextile will provide the necessary support over the resulting cavity at the joint. Numerical modelling and laboratory testing were carried out, to verify if the designed waterstop could sustain without breaking deformations up to ≈ 30cm in vertical and horizontal directions. Modelling and testing were successful. The external SIBELON® geocomposite waterstop was installed in 2012 and performance up to date is very satisfactory as predicted.


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Presas Carpi Lámina Pvc

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