An 11001 Diaphragm Wall

20 011 1 MON NITOR RING DIAP PHRAG GM W WALL DISP PLACEMEN NT & A ASSOCIATE ED GR ROUN ND MOV VEME ENT

November 2 2011

ENCARD DIO-RITE ELECT TRONICS PVT. LTD. L

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Monitoring of diaphra agm wall

AN N-11001

APPL LICATION NOTE AN-11001

November 2011

MO ONITORING G DIAPHRA AGM WALL L DISPLAC CEMENT & ASSOCIAT TED GROU UND M MOVEMEN NT 1. Intrroduction Deep excavation e is a necesssity for con nstruction off structure es like high rise building gs, undergrou und garages and und derground mass m transpo ort systems operating att several levels. In many m such cases construction of a gm wall provid des a solution n as: diaphrag •

They can be constructed in the immedia ate vicinity off s. exissting buildings

•

They can be used not only to secure a dee ep excavation but also as a loa ad bearing me ember for the e structure to be erected; thus t renderring constru uction more econ nomical.

Excavattion in soft grround inducess ground movvement. This may damage adja acent existin ng sensitive structures. Deforma ation must be e limited to acceptable a limits in deep excavation. A stable deep excavvation is one in which the o not collapse e and heave of o base is con ntrolled within walls do limits. In n such cases, diaphragm walls w are com mmonly used as perrmanent retaining wallss to minim mize ground moveme ent. Deep exxcavation sup pport systemss have two ma ain componen nts: •

Retaining wa all

•

Support prov vided for retain ning wall

Principa al types of reta aining walls used u are diaphragm walls (slurry ( with re einforced cage e), sheet piless, soldier piles, co ontiguous pile es, secant pile es and tangen nt piles etc. Principal P typess of supports are struts and d tieback anchorss. This app plication note is about instrumentation and a monitorin ng of diaphrag gm wall displa acement and adjacent moveme ent of the gro ound which afffects structurres in close proximity. p Secction 5 gives some s case sttudies for referencce.

2. Dis splacementt of adjace ent ground due to deep excavation Deep exxcavation has s two main efffects. Firstly,, removal of soil s results in n decrease off weight/stresss on soil below the excavatio on. Secondlyy, it results in loss of la ateral supportt for soil aro ound the excavation. Horizonttal and vertic cal displacem ment that con nsequently occcur have to be kept within acceptab ble limits; otherwisse damage to o any buildingss, roads and underground facilities in th he zone of inffluence will occcur.


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2.1 Fac ctors affectin ng diaphragm m wall move ement Several factors affec ct diaphragm wall movement – type off soil, ground d water condition & chang ges in its level, depth & shap pe of excava ation, type & stiffness of o diaphragm wall & its supports, method of construcction of diiaphragm wall w & adjacent facilities, structural load, duration n of constru uction of wall w & structure e etc. For example, e figu ure on right sh hows increas sed base heave in case of a continuous s sand strata a below the diap phragm wall. Reprodu uced below are a result of studies s by Long g (2001) and Clough C & O’ Rourke R (1990) who collec cted information on ented walls and categ gorized instrume them mainly based on type of so oil and d wa all constructed d. type of diaphragm 2.2 Stu udy on diaph hragm wall mo ovement Table below b shows maximum la ateral wall movement m an nd maximum vertical setttlement behind walls normalizzed by excav vation height. Soils are classified as sofft or stiff soil. Cohesion less and cohessive soils are indiccated. Effect of the factorss of safety aga ainst base he eave and the effect of the type of the su upporting system is also consid dered. Referen nce

Long (20 001)

Type off soil

Max. lateral wall movemen nt normalize ed by excavatio on height, δl max/H (%) Strut Anchor support support 0.13 0.14 (81)* (50)

Max. vertical M s settlement n normalized byy e excavation he eight, δ max/H (%) δv S Strut Ancchor s support sup pport 0 0.11 0.12 2 (35) (15)

0.21 (14)

0.21 (2)

0.39 0 (7)

0.14 4 (1)

0.84 (35)

0.91 (3)

0.80 0 (13)

6.25 5 (1)

Supporrting System Stiff soiils, high factor of o safety of base he eave Soft soiils, high factor of o safety of base he eave, stiff soil at dredg ge level Soft soiils, high factor of o safety of base he eave, soft soil at dredg ge level Soft soiils, low facto or of safetty of base heave

Clou ugh and O’Ro ourke (1990)

Values ass high as 3.2 % have been n recorded for the factorr of safety on the order of 0.9 0

(81)* Number N of cas ses studied

Max. lateral wall Max. verttical move ement settlemen nt norm malized by normalize ed by excavation height, excavatio on height, δl ma ax/H (%) δv max/H H (%) Nott relevant 0.20

0.15

<0.5

>2.0

Table 1: Ma aximum wall movement an nd vertical setttlement behind walls


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2.3 Purpose of insttrumentation n Instrume entation of strructures has several s purpo oses. Some of o them are lissted below: •

To verify and d control consstruction proce ess

•

To verify des sign paramete ers

•

To monitor sa afety during construction c

•

To save cons struction cost

•

To complete construction in time or red duce time of construction c

•

To certify the e performance e of new consstruction/exca avation

•

To monitor sa afety of adjoin ning buildingss and structurres

•

Long term pe erformance monitoring m for safety during life of structu ure

3. Instrumentatiion of deep p excavatio on Deep excavations e are a instrumented before start of anyy excavation. Instrumentation is requ uired for monitoring and con ntrolling beh havior of dia aphragm wa all and surrounding facilities. For example, e entation is req quired to mea asure sub-surface displaccement, which h is not possiible to be dettected by instrume visual means. m It may y also be requ uired to monittor lateral mo ovement or tillt of structures in zone of influence or any cracks c that may develop in n them. Reprroduced below w is a diagram showing tyype of instrum mentation that mayy be used in a deep excavation:


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Monitoring of diaphragm wall

AN-11001

Table 2 below summarizes an instrumentation scheme that can be used to monitor deep excavations. Instruments, like inclinometers, horizontal & vertical extensometers, piezometer, tiltmeters, strain gages and load cells along with surveying methods are extensively used. Inclinometers may be placed in boreholes in the soil and/or in piles or diaphragm walls. Load cells on struts or anchor heads are very useful in checking calculated loads. Strain gages are used in monitoring stress on struts or in piles and diaphragm walls. A word of caution - redundancy in instrumentation must be provided to account for damage that may occur during construction activity. This is very important, especially at critical locations.

Type

Instrument

Purpose

Related problem

Groundwater table/ piezometric pressure

Water Standpipe

Lateral movement

Inclinometer

Seepage and ground subsidence Consolidation settlement uplift or weakening of soil Instability of retaining system and adjacent structures

Stress/load

Vibrating wire strain gage Load cell Sister bar

Change in groundwater level Change in piezometric level Lateral ground movement & deflection of retaining walls Stress along strut member

Settlement/heave

Piezometer

Earth pressure cell/jackout pressure cell Surface settlement point Building/utility settlement point Settlement gage Extensometer

Tilt/crack

Tilt plate/tiltmeter Crack meter

Vibration

Vibration sensor

Axial load on strut Stress in rebar of concrete retaining structure Earth pressure distribution on retaining wall Ground surface settlement

Settlement of adjacent building and utilities Continuous settlement of structures Vertical ground movements in various depth zones Tilt of structures Cracks on structure surface Vibration effect to adjacent properties

Over-load of struts

Over-load of reinforcing bars Over-stress of earth retaining wall Movement of surrounding ground and damage to existing utilities Instability of structures

Deep ground movement

Instability of structures Uneven settlement of structures Disturbance to foundation soils and structures

Table 2: Instrumentation for deep excavation

ENCARDIO-RITE ELECTRONICS PVT. LTD.

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Table 3 below provides guidelines for the installation of instruments: Instrument

Position

Installation

Water Standpipe

Along excavation boundaries and within anticipated groundwater drawdown zone In compressible layers where consolidation is anticipated or below base of potential uplift structures At most critical location generally midspan of excavation boundaries or near sensitive structures On selected strut members

Not shallower than depth of excavation

On selected strut members

Axial

Sister bar

On selected reinforcement

Axial

Earth/jackout pressure cell Surface settlement point

On selected retaining wall panel

Wall surface in contact with soil

Along excavation boundaries and critical sections perpendicular to excavation boundary On selected columns of structures

At 5 m to 10 m spacing and according to existing site condition

Piezometer

Inclinometer

Vibrating wire strain gage Load cell

Building/utility settlement point Extensometer

Within anticipated stress influence zone

Settlement gauge

On selected columns of structures

Tilt plate/tilt meter

On selected columns of structures

Crack meter

On surface of selected structural members At sensitive structure locations

Vibration Sensor

At various depths in compressible layer or expected sensitive location Embedded in rigid base beyond movement influence zone but not shallower than depth of Excavation Web of steel member

On surface of structural member after removal of paint and loose plaster Various depth zones On surface of structural member after removal of paint and loose plaster On surface of structural member after removal of paint and loose plaster On surface of structural member after removal of paint and loose plaster Fixed or portable

Table 3: General guideline for installations of these instruments

4. Planning a proper instrumentation scheme An instrumentation scheme should be properly planned and result oriented. It should provide for safety during construction activity and if required even after that. The following should be taken into consideration: 4.1 Site and project conditions Site and project conditions such as type of soil, depth & size of excavation, method of construction and location/type of structures in zone of influence should to be carefully analyzed during planning of the instrumentation system. Instrumentation scheme varies from location to location. It should be carefully decided after review of all data available for the project and the site.


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4.2 Selection of monitoring instruments Several types of instruments are available. Only the right type must be used to provide engineers with correct information on behavior of ground and structure during excavation, taking into consideration absolute safety during construction. In selection of instruments table 2 provides some guidelines. 4.3 Layout of instrument locations Selecting proper locations of instruments is as important. Instruments should be installed at the most critical and representative locations to accurately monitor influence of excavation on surrounding properties to determine response of ground & retaining system and to ensure the safety of construction. Table 3 provides guidelines for planning instrumentation locations. 4.4 Technical specifications and method statements Technical specification should include type of instrument, range, precision and accuracy etc. Method statements including notes for installation should be properly prepared. It is important that required specifications are fully complied with and installation is carried out under the supervision of a competent geotechnical engineer. Initial instrumentation data should be properly recorded and reflected in later interpretation works. 4.5 Checking and maintenance procedure Instruments must be maintained in good working condition throughout the monitoring period in order to ensure validity and accuracy of monitoring readings, especially during long periods of monitoring or frequent applications. Regular checking and calibration at specified intervals should be carried out to verify instrument specifications including those of sensors, read-out loggers and reference points used in the monitoring works. 4.6 Frequency of monitoring Monitoring frequency must be properly planned based upon sequence of construction and type of measurement. For example, more frequent monitoring is needed for inclinometers during excavation in view of its sensitivity to excavation sequences, e.g. excavation and installation, pre-loading and removal of struts and the importance of movement magnitudes to site safety. Representative initial readings of all installed instruments must be properly established prior to commencement of major site activities to ensure reliable reference for future comparison. 4.7 Control values and action plan Two typical control values namely alert level and action level are commonly adopted during deep excavation. These are determined by designer based on result of analysis and his professional judgment. 4.8 Data processing and interpretation Timely analysis of instrument readings by competent geotechnical engineers is essential for control of safety during construction and instituting effective prevention measures (if required) for minimizing detrimental effects and possible failure in deep excavation. Employment of an independent specialist organization for Instrumentation and Monitoring is highly recommended. Verification of instrument readings during monitoring stage by constantly checking top level of water standpipes, top level and co-ordinates of inclinometer casing, reference benchmark for settlement survey and surface protection to instruments is an essential part of any instrumentation and monitoring program.


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Reproduced below are some typical instrumentation results at a Project in Abu Dhabi, UAE:

Typical monitoring results: inclinometer in D-wall

Typical monitoring results: standpipe piezometer inside excavation area


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Typical monitoring results: extensometer outside D-wall

Typical monitoring results: Anchor load cell for ground anchors


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Typical monitoring results: tilt meter for adjacent structures


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Typical monitoring results: building settlement point

Typical monitoring results: multilevel piezometer outside D-wall


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Interpretation of the above data aims at: •

Ensuring construction is carried out safely and to provide data for modifying construction procedure, if necessary.

•

Ensuring that adjacent structures are safe during and after construction.

•

Providing data for evaluating situation should some structure be endangered and preparing contingency measures should action be needed to safeguard these structures.

•

Providing data for taking remedial measures should some structure suffer from damage and evaluating effectiveness of such measures.

•

Providing data for clarifying responsibility in legal cases.

•

Proving data for back analyses for refining design procedures and enhancing construction technology.

5. Case studies 5.1 Office and residential tower, Abu Dhabi, UAE The office and residential tower will have 27 levels. Instrumentation has been provided to monitor behavior of diaphragm wall and settlement caused due to dewatering and deep excavation. Toe level of D-wall is -20 m and final excavation level is -12 m. Instrumentation scheme for monitoring works is as follows: Description

Depth/

Monitoring

position

frequency

Inclinometer

20 m

Anchor bolt load cell (1000 KN) Strain gage

2.5 m from capping beam First layer of strutting

Qty.

Excavation level at -10 m 20

Daily during excavation (if not

10

critical) after excavation weekly

Strain gages for struts


10

Anchor Load cell for ground anchor

Inclinometer installed in diaphragm wall

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Datta presentatiion 5.2 Co orniche Hotell, Khalidiya, Abu A Dhabi, UAE U The eleg gant and bea autiful 35-storrey building has h been de esigned by Surbana S Conssultant Pte. Ltd. L of Singa apore to refle ect the marittime heritage of Abu Dh habi. Since final f excavattion was dee ep, appropriate instrume ents were used u to protect adjacent structures s and re educe grou und moveme ent. To ensu ure ground movement and a deflectio on of wall within acceptab ble limits, thrree layers of strutting was s provided. List of in nstruments us sed are descrribed below:

Descripttion

D Depth/Position n

Monitoring Freque ency

Q Qty.

Inclinom meter

3 m 30

8

Strut load cell (5000 0 KN)

2 m from We 2.5 eller on pipe strut s

23

Spot we eldable strain n gage

A three layer of strutting All

68 Dailyy during excavation

VW piezzometer

O Outside D-walll

Water standpipe s

O Outside D-walll

Tilt platte

O sensitive structures On s nea arby

Crack gage g

O sensitive structures On s nea arby

58

Vibratio on & noise re ecorder

4 location

1


(iff not critical) after a exxcavation wee ekly

7 7 4

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Strutting works on site

Inclinometer in D-wall

Load Cell on strut

Load Cell on strut (close view)

Stain gage on pipe strut

Stain gage on pipe strut (close view)

5.3 Jumeirah village, Dubai, UAE Jumeirah Village encompasses more than 6,000 spaciously constructed villas and town houses set amidst luscious landscaping and unsurpassed leisure and lifestyle amenities to provide a great living experience for its residents. For monitoring lateral movement and load on diaphragm wall at JOURI 5 and JOURI 6 (part of Jumeirah village development), client specified installation of inclinometers and strain gages. Toe level of D-wall was at -19.0 m and excavation level was at -15.50 m. List of instruments used is as follows: Description

Depth/Position

Inclinometer

19 m

Embedment strain gage

At four levels in d-wall panel


Monitoring Frequency Weekly

Qty. 4 16

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Layout plan of Jumeirah Village

Monitoring of strain gage at Jouri 5

Inclinometer in diaphragm wall 5.4 Al Quds Tower, Doha, Qatar The 101 floors, 420 m tower project presents a real challenge for the creation of an innovative and magnificent human habitat as one of the greatest landmarks of Doha. The target is to host more than 2,000 inhabitants in an icon building that could be symbolically linked with Al Quds through an analogy with the Dome of the Rock at Jerusalem. The Arabic name of Jerusalem is Al Quds or Baitul Maqdis. The golden Dome of Rock at Jerusalem is one of the most important and ancient monument of Islamic culture. According to Islam, it is the place where prophet Muhammad ascended to God in the heavens and symbolically the Al Quds Tower would do the same. The foundation works includes a diaphragm wall all around the structure. The toe level of diaphragm wall is at -30 m. Excavation level is up to -24 m. A large quantity of instruments as per specification of designers were supplied and installed during excavation/foundation works and behavior of diaphragm wall was closely monitored. The site is surrounded by a number of high rise buildings. Before constructing the diaphragm wall and the start of excavation, a pre-construction condition survey of all the buildings in the zone of influence was undertaken. The foundation and the diaphragm walls were constructed by of Ammico Contracting Co. W.L.L. Instrumentation for the diaphragm wall was provided by the Encardio-rite Group of Companies.


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Typical installation of anchor bolt load cell

Description of instruments supplied:

Instruments

Qty.

Inclinometer- 30 m

20

Jack out pressure cell

15

Anchor bolt load cell

12

Sister bar

30

Tilt plate

10

Portable tilt meter

1

Crack meter- 50 mm

10

Readings from portable readout

Typical installation of jackout pressure cell


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5.5 Co onvention Ce entre and Tow wer, Doha, Qatar Q Anotherr great symbo ol in Qatar’s desire d to crea ate world-classs architecture e is the Doh ha Convention Centre and d Tower whicch will bring a truly futuristic aspect to t the Doha skyline. s Scheduled to be completed c in 2012, the tow wer will soarr 105 stories into the sky and offer a panoramic city c view from m its prestigio ous central location on the Corniche. It will be home to offices on the lower flo oors, a hotel with w 300 guesst rooms, 80 serviced apartments and 300 3 residenttial apartmen nts. The Con nvention Cen ntre, adjacen nt to the tow wer having 87,000 8 square e meters of co onvention spa ace is destine ed to become e an importan nt regional an nd internationa al exhibition location. The pro oject includes s 2 ~3 levels basement covering c the full plot area a. A proper retention r sys stem was the erefore necesssary, which comprised of o a diaphrag gm wall, sec cant pile walll and ground d anchors. Excavation de epth inside re etaining wall is up to -14 4 m. The fou undation and diaphragm wall w construcction were in the scope of o work of Am mmico Contracting Co. W.L.L. Instrume entation for the t diaphragm m wall was pro ovided by Enccardio-rite. Instrume entation was specified forr monitoring ground and wall moveme ent, dewaterring water con ntrol, and ancchors. Inclino ometers were used to mon nitor horizonttal deflection of secant pile e wall and D--wall up to 5 m below the toe level of pile wall. Ground anchors were monitorred with anchor bolt load cells c and grou undwater with h piezometer.. List of instru uments used for the foundation works iss as follows: nts supplied d: Description of instrumen Instrruments

Qty.

Anc chor load celll 1500 kN

6

Inclinometer 30 m Watter standpipe e 12 m

35 12

Watter level soun nder 30 m Jack out pressu ure cell Sistter bar

15 9 70

C Convention Centre C and Tower, T Doha

5.6 Dubai Metro Un nion Square Undergroun nd Station, Dubai Union Square und derground metro m at Deira, Dubai, station was extensivvely instrume ented to mo onitor key geo-technical parameters, succh as deforma ation of diaph hragm walls using inclinom meters and 3-D deform mation targets, strut loads using electtronic load ce ells & strain n gages, su urface settleme ent and settle ement of utilitties & adjacent structures s using su urface settleme ent points & building b settle ement points, ground water w drawd down


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outside excavation using water standpipes and monitoring of pumping activities in pump wells within excavation using water level indicators. Depth/Position

Inclinometer in diaphragm wall Inclinometer in ground Strut load cell (2000 kN)

47 m 52 m On layer A struts below concourse level (2 no. on each strut) On layer A struts below concourse level (2 no. on each strut) Outside excavation

Spot weldable strain gage

Water standpipe (including existing standpipes & observation wells for pumping tests) Pump wells Surface settlement points Building settlement points Diaphragm wall 3-D deformation monitoring

Strut load cell

Monitoring Frequency

With-in excavation Outside excavation/ on utilities On surrounding buildings On diaphragm wall below concourse level

Daily during excavation (if not critical) after excavation weekly

Description

Qty. 9 2 6

14

36

17 211 21 14

Inclinometer readings being taken

The observed data was processed and uploaded on client’s server both in graphical and numerical formats


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on a da aily basis. The e server, which was accessible by all concerned parties includin ng the Engineer, also containe ed other use eful informatio on such as as-built instrumentation layouts, monitoring contro ol values (MCV) viz. v alert, action and maxim mum permisssible values (M MPV) for various instrume ents, previouss & latest weekly reports, MCV V breach forms, instrum mentation picttures, instrum mentation ca alibration reco ords etc. eport issued contained su ummary of alll instrumentation & monito oring related activities Weekly monitoring re during th he previous week. w Alert, action a & MPV V forms were issued within n 24 hrs of any breach off MCV by any instrument. Encardio o-rite execute ed the comple ete instrumentation & monitoring works not only of th he above underground & annual station on o a turn-key basis: supplyy, testing, insttallation, mon nitoring, factua al reporting, maintenance m calibratio on, but also for nine othe er undergroun nd stations and a six annexxed structure es of the Dub bai Metro Project.

Typical readings s observed in n inclinomete er installed in diaphragm m wall post TBM break-through


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6. Concluding remarks It is seen that Instrumentation and monitoring plays an important role at both design and construction stages. The construction of high rise buildings and other structures through deep excavation is well benefited from the instrumentation and monitoring program. The data observed from monitoring instrumentation as described above, provides verification of design assumptions. It also helps to manage the construction in a safe and controlled manner, protecting adjacent buildings/structures. The researches carried out, based on the instrument readings obtained during ongoing excavation works, have greatly enhanced the construction technology in several parts of the world. Based on our successful experience, it is recommended that: 1. In construction projects of significant size, particularly those involving deep excavations in densely populated area, sufficient emphasis be given to instrumentation and monitoring. 2. More importantly, specialists must be engaged in processing, interpreting and utilizing the data obtained. 3. Web based remote Data Monitoring Services (WDMS) from Encardio-rite makes instrument data available online. The service can be judicially used for monitoring displacement & ground water pressure in the diaphragm wall or in its vicinity, or to provide relevant information related to safety of construction works and associated buildings, to various authorized personnel like engineer, client, consultants, project manager etc. Encardio-rite WDMS consists of a data collection agent, a data base server and a web server software hosted on a high integrity server machine that periodically collects data from remote EDAS-10 data loggers, which can be geographically spread over a large area, over cell phone network. The web server then makes this data available over the internet so that a user can view the logged data using a suitable web browser like Microsoft Internet Explorer from virtually anywhere in the world. The WDMS allows the user to view the data from any transducer connected to the remote datalogger over a selected time period in either a tabular spread sheet type format or as a graph. A graphic like a map, ground plan or a photograph can be put on the opening screen marked with installed sensors. The WDMS can also be programmed to send SMS alert messages to selected users as soon as any sensor data crosses its predefined alarm levels. Encardio-rite provides a complete range of geotechnical and structural instrumentation along with technical support to the construction industry in form of installation, monitoring, method statements, manuals, application notes, etc. such that it can benefit and improve its quality of work and competitiveness.


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An 11001 Diaphragm Wall

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