Diaphragm wall IS code

8/12/2019 Diaphragm wall IS code

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Is 14344 : 1996

I ndian St andard

DESIGN AND CONSTRUCTI-ON OF

DIAPHRAGMS FOR UNDER-SEEPAGE

CONTROL - CODE OF PRACTICE

I CS 93.160

0 BIS 1996

( Reaffirmed 2001 )


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Foundation and Substructures Sectional Committee, RVD 8

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by theFoundation and Substructures Sectional Committee had been approved by the River Valley DivisionCouncil.

Construction of conventional rolled earthfill cut-off benches can be a prohibitively expensive operationdepending on the required depth and the existing natural ground water condition. The recent trend hasbeen towards application of diaphragm walls in the control of under-seepage.

Diaphragm walls can be constructed by a variety of methods that do not require foundation dewatering

and greatly reduce the amount of excavation from that required for a rolled earthen cut-off.

In theory, all the major types of diaphragm walls can be designed to provide a positive seepage cut-off.However, there are certain uncertainties in the design and construction of all types of diaphragm walls.Each application of a diaphragm wall is unique and depends largely on the intended function as on thefoundation conditions, hydraulic gradients~and economic considerations. In this standard the design andconstruction aspects of diaphragm walis have been addressed to the situation where the diaphragm walls used as a measure for under-seepage control.

For the purpose of deciding whether a particular requirement of this standard is complied with, the finalvalue, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordancewith IS 2 : 1960 Rules for rounding off numerical values ( r evi sed ). The number of significant placesretained in the rounded off value should be the same as that of the specified value in this standard.


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IS I4344 : 1996

I ndian St andard

DESIGNANDCONSTRUCTIONOF

DIAPHRAGMSFORUNDER-SEEPAGE

CONTROL-CODEOFPRACTICE

SCOPE

1 This standard covers the design and construc-on of diaphragm walls to be used as positive im-ervious cut-offs for dams, weirs and barrages as annder-seepage control measure.

2 Diaphragm walls required for other structurese not covered in this standard

REFERENCES

1 The Indian Standards given in Annex A areecessary adjuncts to this standard.

2 For the definitions~of various terms used in thisandard, reference may be made to relevant partsf IS 4410.

GENERAL CONSIDERATIONS FORIAPHRAGM WALL AS AN UNDER-SEEPAGEONTROL MEASURE

1 Under-seepage control measures for dams,eirs and barrages have two independent func-ons:

a) To reduce the loss of water by seepage,through sub-surface, to an amount com-patible with the purpose of the project; and

b) To eliminate the possibility of structuralfailure by piping.

.2 The quantity of seepage can be reduced ap-reciably by intercepting the pervious strata by

means of diaphragm wall. Bottom of the diaphragmwall should be embedded in continuous impervioustratum. Top of the diaphragm wall should be con-ected with an impervious membei of the structureke the impervious core of embankment.

.3 Chances of failure of dam by piping increasesapidly with increasing value of hydraulic gradient.

Careful selection of the type of diaphragm wall caneduce the probability of piping failure to a mini-

mum.

.4 Selection of under-seepage control measures is

c) The economic value of the water stored,d) The risk element asinfluenced~by the height

of dam,e) Reservoir volume, andf,) Potential damage to -downstream areas.

4 NECESSITY OF DIAPHRAGM WALL4.1 Where construction of positive cut-off trenchby conventional open excavation is not feasible onaccount of the situations described below, con-struction of diaphragm wall as an under-seepagecontrol measure can solve the problem:

a>

b)4d)e)

Excessive depth of the impervious stratumoverlain by pervious or heterogeneousstrata;Construction difficulties, like heavydewatering;Instability of side slopes of excavations;Paucity of construction materials; andTime constraints, etc.

4.2 It is, however, imperative to study the costfactor, water loss that can be tolerated, risk in-volved in case of failure of structure, ease in con-struction, time factor, and any other inherent issuesfor the project, prior to selecting the under-seepage

control measure.

5 TYPES OF DIAPHRAGM WALL

5.1 Depending on the use of constructionmaterials there are the following types ofdiaphragm walls:

a) Rigid type1) Reinforced cement concrete.

b) Flexible type

1) Plastic concrete,2) Cement bentonite slurry trench, and3) Earth backfilled slurry trench.

5.2 Diaphragm wall, single line or two lines spacedabout 3 to 4 m apart can be provided as per therequirements of water tightness and site conditions.


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6 SELECTION OF TYPE OF DIAPHRAGM or cement bentonite diaphragm wall or earth back-WALL filled slurry trench diaphragm wall.

6.1 Selection of type of diaphragm depends upon 6.3.2 If sub-surface strata consists of gravelly or

a number of factors such as: bouldary deposits with the interstices filled up with

site conditions; finer soil particles forming a tight matrix of relative-

heterogeneity/perviousness of sub-surfacely low permeability, plastic concrete diaphragm is

strata; preferable to rigid or cement bentonite slurry

geological features:trench diaphragm.

a)

b)

Cld)e>

9g>

Y Y

depth of overburdyn; 7 NECESSARY INFORMATION

anticipated stresses and deformations dueto embankment construction and reservoir

7.1 Following information is generally necessary

loading conditions;for the design and construction of a diaphragm wallfor under-seepage control:

availability of construction materials; andtechno-economic considerations, etc.

a) Contoured site plan and detailed drawingsof embankment dam/barrage/weir withproperties of soil in various zonks of em-

bankment dam, showing FRL, MWL, LWL,TWL, etc.Detailed sub-soil investigations along theproposed alignment of diaphragm wall aslaid down inIS 1892 : 1979 and IS 6955 : 1973with particular reference to the boul-dary/gravelly formations.Longitudinal section along the proposedalignment of diaphragm wall marked withground levels, sub-surface geological fea-

tures, type of structure(s) at both ends ofdiaphragm wall and any other pertinentdetails.

IS 14344 1996

6.1.1 Guidelines given in this standard are only anindication of the preferred type of diaphragm wall.The decision of the design engineer backed by as-sessment of various factors, past experience and hisown judgement are important in selecting a type of.diaphragm wall to suit the project requirements.

6.2 Where the foundation strata consists of boul-dary deposits, open gravel pockets, zones of talus,slide areas, contacts of formation of differentgeological age, fractured zones or similar features,

it is obvious that voids/openings may be larger andcontact with diaphragm wall face may not be con-tinuous. Under such circumstances it is import,antto see that bending stresses between contact freelengths are taken care of. Any flexible type ofdiaphragm wall which undergoes large deforma-tions at low stress levels is not suitable. Rigid typediaphragm wall is preferable under such condi-tions.

6.3 If stratum in the foundation is fairly uniformand pervious, the contact of soil particles with theface of diaphragm wall will be continuous. Ap-plication of rigid diaphragm wall in such stratainduces higher stress level due to low deformabilityof the fill material of the diaphragm wall, whenpervious strata undergoes strain on load applica-tion. This causes interface problems betweendiaphragm wall faces and surrounding strata whichmay ultimately result in cracks between soil andface of diaphragm wall leading to probability of

hydraulic fracturing. Under such circumstances theideal material for the diaphragm wall would be onewhich possesses deformation characteristics com-patible with the surrounding soil mass. Flexibletype of diaphragm wall is, therefore, preferable insuch circumstances.

b)

Cl

d)e)

f)

g)

h)

0

k)

ml

In-sim permeability test data.Stress-strain curves of embankment andoverburden soils obtained in triaxial sheartest in appropriate test conditions, coveringfull depth of overburden.Physical, physico-chemical and engineeringproperties of the sub-soil and chemical

properties of ground water.Modulus of sub-grade reaction of the sub-soil in horizontal direction.Stage of construction or details of the con-struction sequence and constructionschedule of the embankment dam/barrage/weir.Ground water table, its probable fluctua-tions and subterranean. flow conditions, ifany.

Size, weight, capacity and working principleof the trenching and concreting machineryintended to be used.Quality and amount of local materials avail-able economically at, or near, the site ofconstruction for preparing theslurry, plastic


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hauling units, mixing devices, pumpingdevices, etc, intended to be used.

8 MATERIALS

8.1 Cement

Cement shall be ordinary Portland cement con-

forming to IS 269 : 1989 or rapid hardeningPortland cement conforming to IS 8041: 1990, blastfurnace slag cement conforming to IS 455 : 1989 orPortland pozzolana cement conforming to IS 1489(Part 1) : 1991 or IS 1489 (Part 2) : 1991.

8.2 Aggregate

The aggregates shall conform to IS 383 : 1970. Wellgraded coarse aggregate of 20 mm size shall nor-mally be used in reinforced concrete diaphragmwalls. For plastic concrete diaphragm walls, asmaller size of aggregate may be used.

8.3 Sand

Well graded sand consisting of 50 percent coarsesand shall be used.

8.4 Water

Clean water free from deleterious impurities, asspecified in IS 456 : 1978, shall be used in preparingthe concrete mix and for preparation of bentonite

slurry. Water shall be free from salinity when usedwith bentonite.

8.5 Admixtures

If required, chemical admixtures in concrete shallbe used as specified in IS 456 : 1978.

8.6 Reinforcement

Mild steelbars conforming to IS 432 (Part 1) : 1982and cold worked bars conforming to IS 1786 : 1985shall be used.

8.7 Bentonite

Bentonite used shall conform to IS 12584 : 1989.

8.8 Clay

Clay shall conform to IS 1498 : 1970. Clay isgenerally used to reduce consumption of bentonite.Clay is also required to be used in earth-backfilledslurry trench cut-off walls.

9 DESIGN CONSIDERATIONS

9.1 General

9.1.1 Utmost consideration shall be given, whiledesigning the diaphragm wall, so as to achieve:

a) perfect embedment at both the ends, toavoid/minimize possibilities of crackingb th ithi d di g th di h g

IS 14344 : 1996

b) imperviousness or water tightness. Watertightness is mainly adjudged with the valueof permeability (K). If the water is suffi-ciently expensive to justify a high cost ofdiaphragm~wall then the diaphragm may beconstructed to achieve a permeability of 1,2or 3 lugeons. If the seepage loss is little orof negligible value, then water tightness upto a permeability of 3 lugeons is preferred toprevent piping of the foundation material.Permeability of 3 to 5 may be permitted inexceptional cases where an inordinatelyhigh expenditure is anticipated for achiev-ing of reduction of up to 3 lugeons.

These considerationswill take care of the intended~functions of the diaphragm wall as an under-seepage control measure.

9~1.2 Diaphragm wall is a component of the struc-ture for which dimensions are predetermined. Themost important consideration in the design of adiaphragm wall is to form an impervious wallhaving flexibility to avoid cracking. The potentialfor cracking induced by stresses in the diaphragmwall as construction progresses and during firstfilling of the reservoir shall be considered, par-ticularly for rigid type oftwall. Stresses are usually

not a problem unless they cause excessive crackingwhich would negate the purpose of the wall. Forflexible type of wall, its imperviousness, defor-mability compatible with surrounding soil and re-quired unconfined compressive strength are thegoverning factors.

9.2 Location

9.2.1 The best location for a diaphragm wall withina structure is where the loads are reasonably

balanced on both sides of the wall. In case of newearth/rockfill dam, the axis at top of the dam will bean ideal location due to more or less symmetricaldesign. At this location bending moments aboutthe horizontal axis will be minimum and thehorizontal deformations will also be minimum.However, for any location of the diaphragm wall,the junction of diaphragm wall with its surround-ings has to be properly taken care of to avoid pipingproblems through interfaces (see 9.4.2).

9.2.2 An alternative location of the diaphragmwall is at the upstream toe of earth dam whichminimizes the possibility of compressive failure ofthe wall due to negative skin friction developed bysettlement of foundation strata under the weight ofembankment. For this location, however, construe-,


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IS 14344 : 1996

of diaphragm wall should be connected with ahorizontal impervious blanket which shall belinked with the upstream toe of impervious core.

9.2.3 Location of diaphragm wall is often in-fluenced by site conditions. Location shall, there-fore, be decided after careful study of site

requirements and localised features.9.2.4 Locations of the diaphragm wall required forthe barrage/weir are fixed from design point of view.These are generally -provided at upstream anddownstream ends of the floor of the barrage/weir.However, the junction of the diaphragm wall, otherthan rigid type of diaphragm wall, with the con-crete/masonry work has to be properly thought of.Generally the barrage/weir floor is constructed ofrigid concrete or masonry with concrete cover. Thejunction of rigid concrete in the floor with the

flexible type of diaphragm wall may not bemonolithic and hence in such cases seepage cantake place through such joints. It is, therefore,preferable to use rigid concrete diaphragm walls toact as cut-offs for barrageheir structures.

9.3 Choice of-Panel Dimensions

9.3.1 Choice of panel dimension depends onvarious considerations as below:

a)

b)

C>

d)

e)

Stability: In general, short panels are stablerthan long panels. However, in soft ground

short panels are preferred.Concreting: It shall be possible to place thetotal volume of the concrete for a panelbefore setting, or significant stiffening,takes place.Excavation Equipment: It shall be ensuredthat the panel length shall not be shorterthan a single bite of the grab.N umber of St op- End Tubes: Placing and ex-traction of stop-end tubes is costly.Reinforcement: Size and weight of each

reinforcement cage must allow easy han-dling with available equipment at site.

9.3.2 Each joint is a potential source of seepage. Itis desirable, therefore, that the number of paneljoints shall be kept to the minimum. An ap-propriate size of the panel shall be selected on thebasis of considerations (a) and (b) above. This sizeshall then be analyzed for consideration (c) andthen the remaining considerations taken care of.Panel volume shall be of reasonable size andmoderate in 1engt.h because of the possible

shrinkage of panels. Final checks shall be made onthe closing panels.

9.3.3 A practical maximum panel length shall be ofthe order of 10 m wherein concrete can effectivelybe placed using two tremie pipes in a panel of 600

mm thickness. Minimum panel length shall belimited to 5 m, or single bite of the grab, with onetremie pipe for ensuring due concreting operations.

9.3.3.1 In case of flexible type of diaphragm wallpossibility of seepage through joints gets reducedto a.greater extent. In such cases panel length of

3 m to 5 m will be convenient. Problems of instabilityof sides of trench and handling/circulating the slur-ry will be minimum with these panel lengths.

9.3.4 In general diaphragm walls are of thickness500 mm, 600 mm, 750 mm and 900 mm. Thesewidths have been found to be satisfactory up to adepth of 50 m. For greater depths thicker walls(1 000 mm to 1 500 mm) may be used ensuringtrench stability and resistance to hydro-fracturing.

9.3.5 Depth of the wall will depend on the depth toan impervious layer, or a layer that satisfies thedesigners criteria for allowable seepage losses, andflow pattern.

9.4 Joints, Junctions and Sub-surface Grouting

9.4.1 Joints

9.4.1.1 In case of rigid diaphragm wall, joints be-tween the primary and secondary panels aregenerally achieved by use of form tubes (stop-endtubes). The concrete faces of the primary panels are

roughened using special tools prior to concretingthe secondary panels.

9.4.1.2 In case of a rigid type single diaphragm.wall,the joints between the successive panels aregenerally grouted in accordance with IS 4999 : 1991on upstream face, by method of grouting .throughtubes with sleeves (tube-e-manchette groutingmethod) which is usually adopted for grouting ofalluvium. In doing so, joints between the panels aresealed from the upstream side.

9.4.1.3 In case of two lines of rigid type ofdiaphragm walls, alluvium in between the two wallsshall be grouted, if warranted, by the methoddescribed in 9.4.1.2 to achieve better reduction inpermeability.

9.4.1.4 Flexible type of diaphragm walls can beconstructed without any joints as a continuous con-struction process. However, faces of primary panelsare required to be roughened by grab teeth or byspecial tools, prior to filling the secondary panelsto get a better joint.

9.4.1.5 Interface between the bottom end ofdiaphragm wall and bedrock/impervious stratashall be grouted to achieve water tightness. Thiswill be achieved while grouting the strata below thebottom of the diaphragm wall.


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9.4.2 Juncti ons

9.4.2.1 Junctions of the diaphragm wall willgenerally be at the following locations:

a)

b)

4

Junction of the bottom end of thediaphragm wall with sub-surface strata.Junction of the diaphragm wall at both endswith hill abutment/any structure.

Junction of the top end of the diaphragmwall within the structure.

9.4.2.2 Bottom end of the diaphragm wall shall bekeyed to a depth of 600 to 1000 mm into impervioussoil or rock.

9.4.2.3 At the junctions of rigid and flexible typesof wall with hill abutments, or any structure, it isnecessary to provide adequate creep length to getsafe exit gradients. Diaphragm walls shall, there-fore, extend into the abutment or any structure

to a minimum length which provides safe seepagegradient not exceeding 4 horizontal to 1 vertical.Panel length adopted for construction ofdiaphragm walls should, however, be adjustedaccording to the required extension.

9.4.2.4 Top end of diaphragm wall, whether ofrigid or flexible type, will remain either below theground level or will extend above the ground levelinto an impervious core. Extent of the embedmentof diaphragm wall into the core can be betterdecided with the help of finite element analysis.Without such study, extension of the diaphragmwall into core will be based on the designers judge-ment. Excessive internal hydraulic gradient can beavoided by proper selective treatment around thediaphragm wall in core, type of impervious soil,width of impervious core, downstream drainagearrangement, etc. In absence of finite-element studyit is apprehended that the diaphragm wall candamage the impervious core as the foundation set-tles under the weight of the embankment and sub-

IS 14344 : 1996

sequent loadings. During earthquake, top portionof the diaphragm wall will be more vulnerable todamage. Extension of rigid type of diaphragm wallis not desirable from such considerations. Hence,precautions shall be taken to prevent possibledamages along the extended length of diaphragmwall into the core. Alternatively, it would bepreferable to provide a partial cut-off-trench belowimpervious core to a depth required by permissibleinternal hydraulic gradient considerations, and tokeep the top of diaphragm within the imperviousbackfill of the part+ cut-off-trench up to groundlevel, or below. This also reduces the possibility ofdamage to the diaphragm wall near the groundduring earthquake.

9.4.2.5 Top end of the diaphragm wall shall berounded to avoid stress concentration at thecorners.

9.4.2.6 Whether the diaphragm wall is extendedinto the impervious core, or is kept below theground level within partial cut-off-trench, a coverof plastic clay shall be provided around thediaphragm wall to safeguard against any possibledamage to the wall or to the impervious core. Thiscover shall consist of clayey soil of relatively highplasticity with its liquid limit more than 50. Thisclay cover will act as a deformable cushion and willreduce stress concentration. It will also improve

the interface contacts. Dimensions of cover abovetop of diaphragm wall shall, however, be decided onavailable literature/experience/model study, etc.Such treatment will be required for both the rigidand flexible type of diaphragm walls.

9.4.2.7 Junction of flexible type of diaphragm wallswith rigid structures shall be avoided.

9.4.2.8 Typical juncrion details of rigid/flexiblediaphragm wall with impervious core are shown inFig. 1.

Alldimensions n millimetres.


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IS 14344 : 1996

9.4.2.9 Qpical junction details for diaphragm-walllocated upstream of the toe of earth dam are~shownin Fig. 2.

9.4.3 Sub-subsurface Grouting

9.4.3.1 The bed rock below the rigid and flexibletype of diaphragm wall is generally grouted to arequired depth by providing pipes inside the panels

while casting, to reduce the permeability of bedrock. Drilling the holes directly into the diaphragmwall after its casting shall be avoided as it is practi-cally impossible to keep the holes within the wall.Also in doing so there is a risk of disturbing thepanel material and thereby damaging the wallduring drilling.

9.5 Loading on Diaphragm Wall

9.5.1 A diaphragm wall is a structural componentembedded in soil, analysis shall, therefore, involve

soil-structure interaction. A diaphragm wall,whether rigid or flexible, is subjected to variousloading conditions such as construction of struc-ture for which diaphragm wall is provided, firstreservoir filling and subsequent operating condi-tions. Hence, loading conditions on a diaphragmwall are complex and need careful consideration.Loading considerations also depend upon methodof analysis selected for assessing the behaviour ofdiaphragm wall as well as its location. End of con-struction condition may not be of much importance

if diaphragm wall is so located that loading oneither side is reasonably symmetrical. However,the diaphragm wall located near the upstream toeof the dam/barrage/weir and constructed prior toconstruction of dam/barrage/weir, may undergodeformations in horizontal and vertical directions.In such cases loads due to stresses in horizontaldirection, on account -of post construction ofdam/barrage/weir, are of importance.

9.5.2 In subsequent stages, the maximum loads ondiaphragm wall are expected when reservoir is fully

charged to full reservoir level @XL) and the struc-ture as well as the foundation soil on the upstreamof the diaphragm wall are in completely saturated

state with development of steady state of seepagewithin the embankment. Loads acting on theupstream face of the diaphragm wall may be con-sidered asfollows:

a>

b)

4

9.5.3

Effective lateral pressure exerted by thefoundation soil over the depth of diaphragmwall between ground level and its bottom.Effective lateral stress component con-tributed by the structural load over the en-tire depth of diaphragm wall.Hydrostatic pressure acting perpendicularto the face of the diaphragm wall consider-ing head of water corresponding to FRL.

If an analysis is carried out by finite elementor similar type of method, it is possible to incor-porate all the intermediate loading stages involvingeffect of sequeritial construction. Otherwise wallloadings mentioned in 9.5.1 and 9.5.2 may be

adopted, as the case may be.

9.6 End Conditions

9.6.1 Flexible types of diaphragm walls aredesigned to undergo deformations under loading.Hence their structural behaviour in bending is notof much importance. Only rigid types of diaphragmwalls need structural analysis to take care of bend-ing stresses without developing appreciable defor-mation which may result in cracking.

9.6.2 Structural behaviour ol rigid type oldiaphragm wall is different from any isolated siruc-tural member, as it involves soil structure interac-tion. Till date, it has remained a matter of debateabout end conditions to be adopted for structuraldesign of the diaphragm wall. Considering the em-bedment depth in impervious stratum negligible atbottom as compared to the total depth ofdiaphragm wall and upper end embedded in soil,the end conditions can be considered as hinged atboth the ends. This shall be considered as a guide

only. Depending upon his own experience and/orwith the help of finite element study, the designermay select suitable end conditions.

FIG. 2 JUNCIION DEIAILS OF DIAPHRAGM WALL LocAI~-AI IN IH~ lJww- OFIH~~TOE OF EARTH DAJVI

6


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10 GUIDE LI NES FOR STRUCTURAL DESIGN

10.1 Rigid Type of Diaphragm Wail

10 1 1 Smlctural Analysis

Rigid type of diaphragm wall is to be analyzedeither by the method of beam on elastic foundationor by finite~element method (FEM).

10 1 1 1 Method of beant on elastic foundation

The diaphragm wall shall be considered in planestrain state and as such, unit length of diaphragmwall with entire depth as the span is to be con-sidered as a beam resting on elastic soil media onthe~downstream face. Loads are to be consideredactinz upon the upstream face of the diaphragmwall. Analysis is to be carried out using appropriate

equations for bending moments and shear stressesfor a beam resting on elastic foundation with as-sumed end conditions.

10 1 1 2 Finite elenwzt method FEM)

Finite element analysis takes into account soilstructure interaction. Finite element analysis shallbe carried out either as gavity turn-on analysis orsequential construction analysis. Sequential con-struction analysis is, however, preferred as it takes

into account the elastic modulus of soil changingwith different stress Icvcls during construction. Thefinite clement analysis shall incorporalc intcrlhccclemcnts along the contact boundary of thediaphr;igm wall and surrounding boil mahh. Elimi-nation of intcrfacc clcmcnts results in I;duky stressand displacement computations, due to stresstransfer through common nodes.

10.1.1.3 Finiteelement method lakesconsiderabletime for analysis as well as testing. This aflects the

project schedule. On the orhcr hand, a simplifiedmethod like beam on elastic foundation, in whichsequential construction cannot be accounted for isnot a refined method like FEM. As a compromiseit is recommended to analyze the diaphragm wallby the~method ofbcam on elastic foundation and tocarry out finite element analysis simultaneously asconstruction goes on. After completion of thediaphragm wall, performance shall be evaluated bycomparison of instrumentation observations ofstresses and displacements with those obtained byfinite element analysis.

10.1.2.1 Concrete lor rigid type of diaphragm wallshall bc ol M20 pdc (see IS 4 : 1978). Whcrc

i d i d i ( i id L 01

IS 14344 : 1996

10.1.2.2 The water-cement ratio of concrete usedshall ensure easy flow through tremie pipe used inconcreting. However, the water-cement ratio shallnot be greater than 0.6. The concrete mix shall havethe required slump. 10 percent extra cement shallbe added for under water work.

10 1 3 Design of Reinforrwwt

10 1 3 1 Steel reinforcement is required to beprovided in case of rigid type of diaphragm wall loresist bending moments and shear stresses com-puted as mentioned in 10 1 The design of reinfor-cement that is, size and spacing of bars, minimumsteel requirements etc, shall be carried 0111 n ac-cordance with IS 456 : 1978.

10.1.3.2 An allowance of 10 percent to 20 percentshall be made for a reduction in bond strengh dueto the probability of lodging of sand-laden @ledslurry in case of deformed bars.

10.1.3.3 Reinforcement cage shall be designed forsufficient strength to resist handling stresses.Cages shall be able to resist uplift pressures duringtrcmic concreting and as such adequate tic barsshall be provided. It is imperative that the trcmicpipe passes between faces of the reinforcementcage freely, so that, it is possible to lift and lowerthe tremie pipe frcqucntly during concreting.

10.1.3.4 Spacers shall be provided to the outsidchorizontal main rcinforccmcnt barb at Ircqucnt in-tcrvals along ihc height ofcagc, 10 place the cage inccntrc 01 rhc rrcnch, and Ior easy lowcrin~ 01 he,cage.

10.1.3.5 Rcinlorccmcnt in the diaphragm \+all ihplaced in Ihc form of cages. A single cage can bcprepared if it is practicable to lift the cage and toplocc it in position without distorting the cage.Where it is not feasible to lower the cage in onesection of full height, due to the limitations of theequipment, siteconsiderations etc, the cagcshall bcfabricated in sections. After loweringthe first cagesection and keeping it just projected above theguide walls the following cage section shall bcwelded keeping it suspended above the lowcrcdenc.

10.1.3.6 Connections between the reinforccmcntbars and other steel sections shall be welded withdesign considerations as well as to withstand han-

dling stresses.10.1.3.7 To ensure easy flow of concrete, minimumspacing between reinforcing bars shall not hc lessthan 100 mm.

10.2 I~lesil~le Iypes of I)iaphr:~pl \Vatt

1011 S/ uC/Ll ra/ 4/7tr )~ sr \


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IS 14344 : 1996

earth backfilled siurry trench diaphragm wall arerelatively flexible and capable to deform understresses in the surrounding soil. Hence, develop-ment of stresses is not a design problem. Thesediaphragm walls shall, therefore, be designed toundergo deformations compatible with those in thesurrounding soil without development of cracks.

10.2.1.2 As a whole, the diaphragm wall willdeform due to the following reasons:

a)

b)

C>

d)

Due to the settlement of the structure, thatis, dam/barrage/ weir under its own weight;Due to the settlement and deflection of thefoundation beds under the weight of thestructure;Due to the horizontal deflections duringfirst filling of the reservoir; andSubsequently to the alternating loads re-lated to the use of the reservoir water.

Diaphragm walls shall, therefore, be constructed ofmaterials which possess characteristics towithstand/adjust with such deformations imposedwithout cracking. Ideal materials are those whichgive the deformation characteristics similar tothose of the surrounding soil. In case ofhomogeneous sub-surface soil, or when the varia-tion of Youngs Modulus of overburden soil withdepth is of low magnitude, materials havingYoungs Modulus 4 to 5 times greater than theover-burden soil are adequate.

10.2.1.3 Evaluation of the behaviour of thediaphragm wall shall be made either by elastoplas-tic method or by the finite element method.

10.2.1.4 The governing criteria is that thediaphragm wall shall be impervious.

10.2.2 Concrete Mix

10.2.2.1 For plastic concrete diaphragm wall thewater cement ratio shall not be greater than 0.5.

10.2.2.2 Mix design for flexible types of diaphragmwall needs careful consideration. Modulus of elas-ticity of surrounding soil shall be obtained by con-ducting adequate number of triaxial shear tests inconditions appropriate for loading. Mix shall havemodulus of elasticity 4 or 5 times greater than thatof the surrounding soil. The modulus~of elasticityof the mix shall be obtained by conducting triaxial

shear tests in the same condition under which sur-rounding soil specimens are tested.

10.2.2.3 Mix shall have adequate unconfined com-pressive strength to take the weight of the structure,to resist the soil stresses at depth and to resisterosion.

10.2.2.4 In addition to requirements stated above,the mix shall also possess other properties, that is,durability, erodibility and workability.

10.2.2.5 Mix for plastic concrete/cement-ben-tonite shall have permeability of 10m6 o 10s7 cm/s.

10.3 Earth Backfilled Slurry Trench DiaphragmWall

10.3.1 In this type of diaphragm wall the backfill isgenerally made by mixing the in-situ materials ob-tained with slurry during excavation of the trenchand earth material from additional sources, if re-quired. Ascement is not used, it will not be possibleto obtain compressive strength. Hence impervious-ness is the governing criteria.

10.3.2 Material to be used from additional sourcesshall be impervious clay. Moreover, materials ex-cavated from the trench with slurry shall be thefiner material obtained after screening to removethe coarser fractions. Thus, as such, mix design isnot required for this type of diaphragm wall.

11.1 Requirements of Slurry

11.1.1 Bentonite slurries, used for supporling cx-cavation shall fulfil the following requirements :

a>

b)

C)

d)e>

9

Support the excavation by exerting hydros-tatic pressure on its walls.Remain in the excavation area and not flowinto the soil.Suspend detritus to avoid sludgy layer build-ing up at the excavation base.

Clean displacement by concrete.Screening or hydrocycloning to removedetritus and enable recycling.Easy pumping.

To achieve these requirements the slurry shall haveproperties as given in Table 1. However, they shallbe confirmed to suit the site conditions.


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IS I4344 : 1996

stable 1 Requirements of Slurry(Clause 11.1.1)

Property Method of Test

Density Mud balance or hydrometeryH value pH indicator paper stripsViscosity Marsh cone methodPlastic Fann Viscometer

Viscosity ShearometerIO-minutes gel strength or vane shear apparatusSand content 75-microns sieve

Permissible Value at 20C

1.04 to 1.25 g/ml~9.5 o 1228 to 42 seconds< 2OcP

1.4 to 10 N/m(14 to 100 dyne/L&)1 to 25

11.1.2 Sodium bentonite powder shall bethoroughly mixed with potable water to form a fullydispersed lump-free homogeneous slurry. Suitableslurry tanks shall be used for this operation. Use ofa slurry pump with special nozzle (see Fig. 3) issuggested for preparing bentonite slurry. Use ofpaddle stirrer or other mechanical devices such as

colloidal grout mixer (see Fig. 4), may also be madefor proper mixing of slurry. Temperature of waterand the slurry used shall not be less than SC.

11.1.3 Relationship between concentration C ofbentonite slurry expressed as percentage by massand the density r, is given below:

us = 1.0 + 0.006 C

NOTE - This relation is valid for Indian bentonites andrepresents an average sample. There may be some variationof bentonites. Laboratory calibration may be prepared for

the bentonite samples actually used.

BENTONITE IN

WATER SUPPLY IN

TO TRENCH OR PIT

INSET A

FOLDED WIREMESHOR EXPANDEDMETAL SHAPEDTO FORM FILTER

CONE MIXER

DIAPHRAGM PUMP

FIG. 3 SPECIAL NOZZLE AND SLURRY MIXING PLANI

ENTRANCES SETTANGENTIALLY TO INDUCE VERTEX +

CEMENTWATER MIX-.- ~~PASSED THROUGH TO SECOND DRUM - SECONDARY MIXING OF

CEMENT SAND ANDWATER

GROUTPASSEDTHROUGH THISCIRCUIT FOR INITIAL MIXING

TRAP TO COLLECTSMALL STONESANDOTHER

FOREIGN MATTERS

CENTRAL SHAFT FROM PRIMEMOVER DRIVING PUMP

FIG. 4 FLOW DIAGRAM OF CONCRETE DOUBLE DRUM COLLOIDAL GROW MIXEK

11.1.4 Table 2 gives guidance on the proportion of strength andyH value shall be carried out until abentonite suspension to be used for different sub- consistent working pattern is established, takingsoils based on Marsh Cone viscosity. into account the mixing process, blending of freshly11.1.5 Tests-to determine density, viscosity, shear mixed benlonite slurry with previously used slurry


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IS 14344 : 1996

Table 2 Proportions of Hentonite Suspension for Different Sub-soilsCkzrrse 11.1.4)

Proporlion of Viscosily by

Slorry Iwll Marsh Cone s

1:lO 40-42

1:12 35-40

1:16 33-35

1:20 26-32

ancl any process which is to be employed to removeimpurities from previously used bentonite slurry.

11.1.6 When results show consistent behaviour,the~tcsts for shear strength and pH value may bediscontinued and tests required to determine den-sity and viscosity bc carried out.

11.1.7 Frequency of testing shall be on panel to

panel basis where bentonite slurry becomes heavilycontaminated with fine sand during its first use, andon a daily basis~whcre slight contamination is cx-pcctcd. In cases where a mechanical process isemployed to remove contaminating solids from theslurry, frequency of slurry testing shall depend onequipment employed.

11.1.8 Prior to placing of concrete in any panel abentonite slurry sample shall be taken (about 0.2 mfrom the trench bottom) and the same shall betested for density. The sampling shall be done care-fully by an appropriate method. The density thusdetermined shall not be greater than 1.25 g/ml toensure satisfactory placing of concrete. If the slurryhis ound to have heavier density, the same shall bcthinned till the required density is achieved.

11.1.9 Suitable slurry pumps, submersible pumpsor air lift pumps shall be used for replacing thecontaminated slurry at the bottom of trench byfresh bentonite slurry.

11.2 Stability of Slurry Filled Trenches

11.2.1 Mixing of bentonite in water forms slurry,which is used during excavation of the trench fordiaphragm wall. Water from the slurry bleeds intothe sides of the trench and leaves behind a thindensely packed collection of colloidal particlescommonly referred to as a filter cake. Hydrostaticforce of the slurry, acting in combination with filtercake, provides stability to the sides of trench.

11.2.2 Bentonite slurry filled in the trench impartsstability mainly by applying hydrostatic pressure

on the wall, against the impermeable thin filmformed along thewall. Secondly, the slurry filled inthe trench provides passive resistance againstfailure of the trench, and thirdly, the shearing resis-tance of the slurry saturated zone and the plastering

effects of the filter cake also contribute towardstrench stability. Hydrostatic pressure alone repre-sents 65 percent to 80 percent of the total stabiliz-ing forces. If the density of slurry used can providea factor of safctyofone, due to hydrostatic pressure,then the factor of safety of the actual trench shallbe between 1.25 to 1.50. Therefore, taking onlyhydrostatic pressure and consideringF= 1, the den-sity of slurry may be calculated as indicated by thefollowing formula. This formula shall be used as aguide only.

F=Nc Cu

H r - )S)

whereH =C =r =

Ts =

A, =

depth of the trench,undrained shear strength of clayey soils,

natural density of saluratcd soil,density of the slurry needed for thetrench, andbearing capacity factor which varies from4 at the ground surface to 8 for deeperdepths, depending upon D / B and L I Bratio of the trench. This factor accountsfor arching action in horizontal as well asvertical directions (see Fig. 5).

B For snnd y soils :

,s = r,v+ A K,l.r )where

A J-C-PI k,, all cp

2n k, tan p

Kn = tan(45 - p/2),

P = angle of internal friction,r = effective unit weight of the sandy soil,

= rsat - rw ,Ysat = saturated unit weight of soil, and

rw= unit weight of water.

The value ofA depends upon depth/length ratio ofthe trench (=n) (see Fig. 6). As a genera1 rule, levelof bentonite slurry in the trench shall be adequatelyhigher than the water level.


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9 LENGTH,z - OFCUT +

n- WIDTH 1)

ii 2 4 6 8 10 12

DEPTH

WIDTHOFCUT +

FIG. 5 STABILITY FACTOR NC FORRECTANGWL,AR UTS IN CLAY

REDUCTION FAGfOR 12 EQUIPMENI AND ACCESSORll2 0.4 0.6 0.6 1 o

n= Zl b

FIG. 6 REDUCTION FACTORA FOR EARTHPRESSURE N TRENCH OF LENGTH 2B (cd=O)

11.3 Additives11.3.1 Where saline or chemically contaminatedground water is present, special additives as listedbelow, have to be used to render bentonite slurry fitfor use. Theseadditives shall be used in very smallamounts of-O. 1 percent to 0.5 percent by mass of theslurry

a)

b)

Ferrochrome lignosulphonate in combina-tion with soda ash or bichromate of soda,shall be used for effective bentonite hydra-tion, if hardness of sea water exceeds 200PPm.Sodium carboxymethyl cellulose (SCMC) isanother additive sometimes used. Itprotects slurry against effects ofelectrolytes, accelerates filter cake forma-

C)

d)

e)

9

1s 14344 : 1996

tion, and reduces fluid loss by increasing theviscosity of slurry.Cement contamination is counteracted byphosphates. Calcium gets removed and claysolids get dispersed. Phosphates decreasepH value thereby lowering viscosity andyield value of slurry.Carboxymethyl cellulose, gums orpresheared asbestos may be used to increaseviscosity and reduce filter loss.To remove fine silty solids and clay solidsfrom the slurry, flocculants such as vinylacetate maleic anhydride co-polymer orpolyacrylamides shall be used. Guar gumcan flocculate clays, carbonates, etc.Pregelatinized starch can be employed as afluid loss control. It can also hc used as ;Iprotective colloid against the effcot of

electrolytes.

12.1 Trerrching Ecluipment

Depending upon the type ofsoil encountered at thesite and the depth, length and thickness of thediaphragm wall to be constructed, suitable trench-ing equipment shall be chosen. General trenchingequipment shall include rotary boring rigs, percus-sion boring rigs, trenching bucket type shovels,mechanical grabs, hydraulic grabs, grabs with kellybars, grabs controlled by suspended wire ropes ofacrane, direct mud circulation boring rigs, reversemud circulation rigs and submersible mortar drillsfor trenching equipment. For gravelly soils,boulder deposits and rock formations, speciallydesigned chiselling equipment shall be considered.If required, methods in combinations of the abovemay be used.

12.2 Slurry Preparation and Testing Equipment

Tanks of suitable sizes and slurry pumps of suitablecapacity shall be used for storage, mixing and cir-culation of bentonite slurry at the site. A separatewater pump shall be used for water supply to slurrytank. Equipment for sampling the slurry from deeptrenches and testing its concentrations, viscosity,pH value and hardness of ground water, in whichthe bentonite slurry and concrete are piepared,shall also be used. Testing of slurry after con-tamination with soil or cement indicates the needof disposal or reuse as the case may be. Vibratingscreens, hydrocyclones and centrifuges for cleaningthe bentonite slurry for reuse shall be employed.

12.3 Concreting Equipment

Concrete mixers, tremie pipes of suitable lengthand size and concrete pouring devices (manual or


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14344 : 1996

echanical) shall be used according to the need ofe work. Lifting arrangement for tremie pipesall be capable of doing the work with desiredeed.

.4 Lifting Devices

ranes of suitable capacity and boom length, der-ck or any other suitable auxiliary rig shall be used

r lowering the reinforcement cage in trench. If theeight of the reinforcement cage and height are

mall, this work can also be done by winch andulley arrangement provided on the diaphragmalling rig. Cranes or rigs with winches of adequatepacity may be used for operating the trenchingabs as necessary.

2.5 Grouting Equipment

anel joints and bed rock below the concreteaphragm wall have to be grouted. Necessaryuipment to perform this job efficiently shall beed.

2.6 General Guidelines

election of trenching shall be made to suit the soilnditions. Vibrations produced during construc-

on shall not have any damaging effect or cause anyrt of instability to existing structures. Considera-

on shall be given to selection of equipment whiche required to work on a site with restricted space

head room.

3 STAGES OF CONSTRUCTION

3.1 Pre-trench and Guide Walls

trench is excavated in advance for about 1 m to 2depth. Reinforced concrete guide walls of 100

m to 250 mm thickness are constructed on bothe faces of pre-trench (see Fig. 7), they act as guides trenching equipment during excavations. Theyso provide support over the trench area subjected heavy construction surcharge pressures. Besides,

uide walls define the planned path of excavation.

DIAPHRAGM WALL

-j-+-j-

II i

All dir&ensionsnmillimetres.FIG. 7 PRE-TRENCH AND GUIDE WALLS

13.2 In soft ground or fill, guide walls have to betaken deeper. When ground water table is close tosurface, guide walls higher than the surface levelshall be constructed to maintain additional slurryhead.13.3 Clearance between finished diaphragm walland guide wall shall be 50 mm minimum, for

straight panels. Clearance shall be suitably in-creased when the panels are curved.

13.4 Finished faces of the guide walls towards thetrench shall be vertical.

13.5 Guide walls after construction shall be suitab-ly propped to maintain specified tolerance.

f3.6 Mesh or cage reinforcement shall be used inguide walls.

13.7 Level of slurry in the trench shall be main-tained at least up to bottom level of guide~walls.However, the level shall be increased if groundwater table is higher.13.8 For heavy trenching machinery, guide wallsshall be constructed with suitable ground slab (onboth sides of the walls).

13.9 Guide walls get support from adjoiningpanels and, therefore, their construction shall bedone continuously.

13.10 Cast In-Situ Diaphragm Wall

13.10.1 Rigid type of diaphragm wall, or plasticconcrete diaphragm wall, shall be constructed by

resorting to either successive panel method or al-ternate panel method. For cement bentonite slurrytrench diaphragm wall, or earth backfilled slurrytrench diaphragm wall, alternate panel methodofconstruction is suitable in view of the time that isrequired to achieve hardness of the mix put in thetrench.

13.10.2 Su ccessiv e Panels M ethod

In this method, a panel shall be cast in continuationof the previously completed panel. Only one formtube is needed for creating a joint with thepreceding panel. However, with larger width andgreater depth of diaphragm wall, it may not bepossible to use form tubes due to handling, lower-ing~and extraction difficulties. In such cases, specialtools, like semi-circular chisels, are used to form ajoint with the preceding panel. Thus, use of ~formtubes is eliminated. Rapid construction is possiblewith this method. However, there is a probability ofinsufficient hardening of the concrete in thepreceding panel with the subsequent possibility ofdamage.

NOTE - Form ubes of 1 m diameter and 30 m length havebeen successfully used.

13.10.2.1 Excavation of successive trench panels(see Fig. 8A) shall be done with the help of suitable

12


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machinery. Trench panels shall be kept filled withbentonite slurry of suitable consistency and vis-cosity during the excavation period.13 10 2 2 stop end tube with a smooth surface ora structural section shall be inserted in the trenchat the end of the successive panel to support con-crete and to form a suitable joint with the next

panel.13.10.2.3 The reinforcement cage shall then beloweredinto the trench panel and shall be suitablysupported. Concrete cover for the reinforcementshall be maintained by use of spacers.

13.10.2.4 Before placing concrete in the panel, thetrench shall be properly flushed to clean the bot-tom and to remove thicker suspension from thebottom and lower levels. Density of the slurry shallbe checked by taking a sample about 0.2 m from thebottom. If the density of the sample is found to

exceed 1.25 g/ml, flushing shall be carried out withfresh bentonite slurry. Concreting in the trenchpanel shall be done through one or more tremiepipes with suitable funnels (see Fig. 8B).

8B CONCRETItiG

FIG. 8 SUCCESSIVE ANEL CONSTRUCTIONEXCAVATION AND CONCRETING)

IS 14344:1996

13 10 2 5 top end tubes shall be taken outgradually after initial set of concrete. This has tobe done carefully with the help of a suitable crane,or any other lifting device, so as not to cause anydamage or cracks in concrete at the panel end.

13.10.2.6 Suitable joints shall be adopted to forma watertight joint between the panels.

13.10.3 Al tern ate Panel M ethod

13 103 1 With alternate panel construction usingprimary and secondary panels, strength developedin concrete will be sufficient before excavating theadjoining panel. Thus, there is no danger ofdamage to the concreted panel. In this method,primary panels are cast first leaving suitable gaps inbetween. Secondary panels are then cast in thesegaps (see Fig. 9). Two stop end tubes are used at theends of the primary panels to support concrete and

to from a joint with the secondary panels.13.10.3.2 Due to the space left by stop-end tubes,primary and secondary panels are of different sizes.The end shape .of the panels will also be different.However, shape of the primary end panel shall besuch as to form a good joint with secondary panels.Other construction techniques are similar to thoseof the successive panel method.

13.10.4 Dir ect Circulation M ethod

13 10 4 1 This method is used with -rotary or per-

cussion type of rigs where drilling fluid (bentoniteslurry) is pumped through drilling rods. It can beused for successive panel or alternate panel con-struction. Stages of construction are shown in Fig.10. Simple trenching rigs for excavation are used.Circular concreting tremie pipes for backfilling thetrench panel have to be used. This method issuitable for shallow depths and for bringing uplighter cuttings.

13.10.4.2 The trench panel is excavated by makingoverlapping bore holes with bentonite slurry- jet in

combination with percussion and to and fro rotarymotion of jetting pipe, having a suitable cutter atthe tip. A special semi-circular cutter shall be usedfor providing appropriate shape at each panel endto form a suitable joint.

13.10.4.3 Operations of filling bentonite slurry inthe trench and lowering of reinforcement cage intothe trench panel are similar to those describedunder successive panel method.

13.10.5 Reverse Cir culation M ethod

13 10 5 1 Th e reverse circulation method shall beused to make trench panels as shown in Fig, 11.Forward and backward movement of the rig fromone end of the panel to the other, increases thedepth of the panel in a zig-zag manner.

13


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14344 : 1996

I = Primary PanelsII= Secondary Panels

TE - Due to space left by stop end tubes primary andondary panels are of different sizes and panel end shape.

FIG. 9 CONSTRUCTION OF PANELS

STAGE 1BORE HOLE STAGE STAGE .3

IREINFORCEMENT

CAGE INSERTION

STAGE 4CONCRETING THROUGH

OVERLAPPING BOR

FIG. 10 STAGES OF DIAPHRAGM WALL CONTRUCTION BY DIRECT CIRCULATION METHOD

0.5.2 High capacity pumps shall be used tok the loosened soil in the slurryfilled trench.

parators, or sedimentation tanks, shall be used toain the soil cuttings and to pass the slurry forculation and reuse.

10.5.3 This method is suitable for greaterths and to bring up heavier cuttings.

13.11 Cement Bentonite Slurry TrenchDiaphragm Wall

13.11.1 For cement bentonite slurry trenchdiaphragm wall it is preferable to use reverse cir-culation method so that bentonite slurry at thebottom of the trench is sucked out along with the

chiselled material.13.11.2 At the end of excavation, the bentoniteslurry in the trench may have much higher densitythan fresh bentonite slurry due to contamination ofsoil. This bentonite slurry shall therefore have tobe replaced by fresh bentonite slurry havingpredecided concentration.

13.11.3 The contaminated slurry is to be replacedby keeping the volume of fresh slurry flowing intothe trench, equal to the volume of contaminatedslurry being pumped out from the bottom of the

trench. This is possible as contaminated slurry isheavier than fresh slurry.13.11.4 After complete replacement with freshbentonite slurry, samples of the bentonite slurryshall be collected from one-third, two-thirds andbottom depths of the panel to check uniformity ofthe slurry in the trench.

13.11.5 After filling the trench completely withfresh bentonite slurry, a required quantity of ce-ment shall be added. Estimation of quantity ofcement required for a panel has to be done consid-

ering full depth of wall, that is, up to platform leveland actual width of trench formed. For this pur-pose, slurry from the trench shall be pumped outfrom the bottom of the trench into a mixing tankhaving proper arrangements for mixing with ce-ment. In this tank cement shall be added bag by bagtill the entire predetermined quantity of cementgets mixed. While adding cement there shall be acontinuous flow of cement bentonite slurry fromthe trench to the mixing tank and from the mixingtank to the trench by gravity, that is, pumped out

and pumped in volume to remain equal. Thisprocess shall be continued till required quantity ofcement is added to the Ijancl. Cement bentoniteslurry shall be kept in circulation for a further 15minutes to ensure uniformity of mix. At the end ofcirculation, samples shall be collected from one-third, two-thirds bottom depths of panel to checkthe uniformity.

NOTE- For proper mixing of cement and bentonite slurryit is very essential to have powerful pumps so that completecirculation of cement bentonite s urry can be achieved for theentire depth of trench within 10 minutes.

13.11.6 After mixing of the cement in a particularpanel, excavation for the adjacent panels can becarried out after allowing minimum 7 days forcement bentonite slurry to attain sufficientstrength. No form tubes are used for joints.


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15.3 Samples of the mix at the time of placing shallbe collected and kept in airtight sealed moulds ofspecified size till due~dates ofvarious tests. Impor-tant tests to be performed are as under:

a) Compressive StrengthThis is the defined stress af which thematerial will fail. Tests shall be carried outat 7,28 and 90 days.

b)

C)

Tri axial Compressive St rength

Triaxial compressive strength tests shall becarried out on filling materials like plasticconcrete, cement, bentonite, etc to deter-mine stress-strain characteristics, modulusof elasticity and shear parameters. Testsshall be carried out at 7, 28 and 90 days inconsolidated undrained conditions.

Permeability

IS 14344 1996

15.2 Mix for rigid concrete, plastic concrete andcement bentonite slurry shall be designed in alaboratory and testing shall be done to ascertainvarious parameters like compressive and tensilestrength, permeability, modulus of elasticity, erodi-bility,pH value, etc, to confirm that the design mixsatisfies the design requirements.

Permeability tests on samples shall be con-ducted after 28 days in a membranepermeameter.

16 INSTRUMENTATION

16.1 Placement of instruments simultaneouslywith casting of the panel is difficult, as there~is apossibility of damaging the instruments, wires, etc,or loosing their sensitivity due to vibrationsgenerated during placement of concrete. Ii is,therefore, preferable to install the instrumentsoutside the completed diaphragm wall to measurein-si tu performance.

16.1.1 Deformat i on of t he Smrct ure16.1.1.1 For the purpose of measuring deforma-tion behaviour of the diaphragm, inclinometers atvarious locations shall be installed close to thediaphragm wall.

16.1.2 Settlement Gauge

Settlement gauges may be installed at selected loca-tions to measure vertical displacements. Gaugesshall not have an error of more than 1 mm.

17.1 Following records shall be maintainedin amanner approved by the Engineer-in-charge:

a)b)Cl

9e)9g>h)j)

Q

m)n)

PIQ)r)

Name of projWwork;Panel No. and reference drawing No;Date of commencement and completion ofexcavation;Date of concreting of panel;Length of panel;Thickness of panel;Top of guide wall level;Depth of guide wall;Top level of wall as cast, in relation to top ofguide wall at rhe edges and al the centre;Depth of panel from base of top of guidewall;Strata encountered;

s)1)

Volume of panel and volume of concreteused, slump, water-cement ratio;Cubes taken and their results;Details of reinforcement (Cage type);Details of any obstructions/peculiar condi-tions encountered and time spent andmeasures taken in overcoming them;Amount of bleeding observed; and5pe and proportion of any additives usedand reasons for use.

16.1.3 Pi ezometr i c Levels

To judge the efficiency in watertightness of thediaphragmwall, residual discharge collected down-strea? of the cut-off wall is the essential measure-ment. This can be determined by a double networkof piezometers placed on either side of the wall andwell protected by filters. Chemical and physicalanalysis of the water may be useful to pinpoint itssource. Observation frequency shall not be morethan 15 days.

16.1.4 .Permeability

100 mm diameter tubes extending to randomdepths, shall be placed at the centre of the thicknessof the diaphragm panels at randomly chosen loca-tions. After a period of 28 days bore holes may bedrilled into the diaphragm below the tubes andpermeability tests by pumping in method carried

out. The in-si tu permeability of the diaphragmshall be compared with the specified limit as perrequirements.

17 RECORDS

16


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Bureau of Indian Standards

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Amendments are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates thatno changes are needed; if the review indicates that changes are needed, it is taken up for revision. Usersof Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of BIS Handbook and Standards Monthly Additions.

This lndian Standard has been developed from Dot : No. RVD 08 ( 141).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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Diaphragm wall IS code

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