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Construction of Diaphragm Wall

Presentation by:

Gagan Goswami

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Content

Introduction

Application

Category of Diaphragm Wall

Construction Procedure

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IntroductionDiaphragm Wall is generally reinforcedconcrete wall constructed in the ground usingUnderslurry technique which was developed inEurope.

The technique involves excavating a narrowtrench that is kept full of an engineered fluidof slurry.

Walls of thickness between 300 and 1200 mmcan be formed in this way up to a depths of 45meters.

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Conceptual sketch showingthe RCC Diaphragm Wall

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Diaphragm wall-Application Commonly used in congested areas

-Can be Installed in close proximity toexisting structure

Practically suited for deep basements Used in conjunction with “Top Down”

construction technique

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Schematic section of DiaphragmWall showing typical use

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Schematic section of DiaphragmWall showing typical use

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Schematic section of DiaphragmWall showing typical use

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Schematic section of DiaphragmWall showing typical use

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Anchoring of Diaphragm Wall usingAnchor Slab

Anchor Slab

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Anchoring of Diaphragm Wall usingAnchor Blocks

Diaphragm Wall

Anchor Bars

Anchor Blocks

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Important ConditionsDictate the use of Diaphragm Wall

Very unstable soil profiles below the watertable

Limited construction time Where deeper than normal cantilever support

may be required

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Positive facades of DiaphragmWall

Can be Installed to considerable depth Formation of walls with substantial thickness Flexible system in plan layout Easily incorporated into Permanent works Designable to carry vertical loads Construction time of Basement can be lowered

considerably. Economic and Positive solution for large deep

basement in saturated and unstable soil profiles. Can be used for seepage control in Dams. Noise levels limited to engine noise only. No vibration during installation.

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Negative Facades ofDiaphragm Wall

Not economical for small, shallow Basements

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Category of Diaphragm wall

1) In Situ Cement Bentonite Vertical Wall2) In Situ RCC Vertical Wall3) Precast RCC Vertical Wall

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In Situ Cement BentoniteVertical Wall

Provides water tight barrier Used to prevent seepage/water loss from

Natural reservoir and Dams

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In Situ RCC Vertical Wall

Underground Structural element Used for Retention systems and Permanent

foundation walls Deep groundwater barriers

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Procedure

Diaphragm Wall construction begins withthe trench being excavated indiscontinuous sections or “panels”.Stop-ends are placed vertically at each endof primary panel to form joints foradjacent secondary panel or closingpanels. Panels are usually 4 to 6 meterslong. Stop-ends are used to form the jointsbetween adjacent panels and a water barcan be incorporated across these joints.

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Construction Method

Secondary Primary

Construction Joint formed byCircular Stopend Pipe

Construction Joint

Schematic Diagram Showing Construction Joint between Adjucent Panels

Secondary Secondary Secondary Closing Secondary

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Construction Method

Primary

Construction Joint formed byFlat Stop end

Construction Joint

Secondary Secondary Secondary Secondary Closing Secondary

Schematic Diagram Showing Construction Joint between Adjucent Panels

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Different Shapes of DiaphragmWall Panel

L-Shape PanelT-Shape Panel

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Different stages of constructionactivities

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Diaphragm Wall Construction Site

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Construction Procedure

Stage-1: Fixing of Alignment Stage-2: Guide wall Construction Stage-3: Trenching Stage-4: Trench Cleaning Stage-5: Stop ends fixing Stage-6: Reinforcement Cage lowering Stage-7: Placing of Concrete Stage-8: Withdrawal of Stop ends

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Guide Wall Construction

Guide Wallis constructed

to fix thealignment of

Diaphragm Wallin the field

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Guide Wall Construction

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Trenching Equipments

Hydraulic Grab Kelly-mounted or Cable-hung cam buckets

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Kelly-mounted Hydraulic Grab

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Cable-hung cam bucket

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Trenching Process

Trenching usually carried out underbentonite slurry

Bentonite Slurry – Key component.-This Slurry acts as shoring to preventcollapse by hydraulic pressure andthyrotrophic property.

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Bentonite Slurry

Used as a support fluid The bentonite suspension used in bore holes

is basically a clay of montmorillonite grouphaving exchangeable sodium cations (Na+).

The action of bentonite in stabilizing thesides of bore holes is primarily due to thethixotropic property of bentonitesuspension.

The bentonite suspension when undisturbedforms a jelly which when agitated becomes afluid again.

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Functions of Bentonite

In case of granular soils, the bentonitesuspension penetrates into the sides underpositive pressure and after a while forms ajelly.

The bentonite suspension gets deposited onthe sides of the hole resulting in theformation of a filter cake in contact withsoil against which the fluid pressure acts.

In case of impervious clay, the bentonitedoes not penetrate into the soil, butdeposits only a thin film on the surface ofthe hole.

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Factors affecting stabilityof Trench

Level of the supporting fluid-Level of the bentonite slurry should bemaintained preferably at least 1.5m above theground water level to avoid problem ofinstability.

Density and Viscosity of supporting fluid Loss of shear strength with time Suction effect during trenching

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Specification of Bentonite(as per IS:2911-Part1:Sec2) Liquid limit : 300 to 450 % (in accordance

with IS:2720-part V )

Sand content : Less than 7 %

Density: 1.12

Marsh viscosity : About 37 second, tested byMarsh cone

Swelling index: Swelling index at least 2 timesof dry volume.

pH value : Less than 11.5

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Tests and compliance values for support fluidprepared from bentonite

(as per IS9556-1980)Property Test method As supplied

to the boreBefore

concreting

Density Mud balance 1.04-1.10g/ml

<1.15g/ml

Viscosity Marsh cone 30 - 90seconds

Shearstrength

Shearometer /Vane shearapparatus

1.4 to 10N/sq.m

pH Digital pH meter 9.5-12

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Schematic Diagram ofBentonite Setup

T1T2T3

•MudPump

Diaphragm Wall Construction area

•Storage tanks

FreshCirculationSettling

Mixer

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Bentonite Setup

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Preparation of Bentonite Slurry

Bentonite slurry made by passing dry powderthrough water jet. A conical hopper is usedwith bottom nozzle through which water ispumped under pressure. The bentonite powderis poured directly from top and when it fallsdown the hopper, it gets agitated in the water.After getting circulated, the mixed bentonitethus falls in the tank.

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Trench Cleaning

Joints of adjacent panels to be cleaned toobtain watertight bond

Loose materials to be lifted by suitable airlifting method

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Fixing of Stop ends

Stop ends to be fixed at the properposition keeping it truly vertical

Distance between two Stop ends to befixed as per prefixed Panel Layout

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Reinforcement Cage

Excavation of panel is followed by placing ofsteel reinforcement cage in center of thepanel.

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Reinforcement Cage fabrication

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Reinforcement Cage shifting

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Lowering of reinforcement cagein the excavated panel

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Resting of reinforcement cagein the excavated panel

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Different stages of construction

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Placing of Concrete

Placing of concrete having slump 150mm to190mm by tremmie method

Concrete to be placed through a top metal hopperand into a rigid leak proof tremmie pipe (2 sets),sufficiently large enough to permit free flow ofconcrete.

Initially there should be a suitable plug at thebottom of metal hopper, which will not dischargeconcrete until sufficient concrete accumulate inthe metal hopper.

concrete displaces the slurry from bottom andrises in such a manner that mixing of concretewith slurry does not occurs

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Placing Concrete

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Placing of Concrete

Pouring shall be continued till itaccumulates in vertical Tremmie pipe upto top of funnel.

Tremmie pipe shall be raised so as torelease the concrete in a single continuousflow.

Concrete to be discharged in the trenchwithout any lateral movement of Tremmiepipe.

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Placing of Concrete

Caution - Bottom end of Tremmie pipemust remains immersed in concrete.

Operation to be continued till goodconcrete reaches 300mm above thecut-off level of Diaphragm Wall.

This concrete above cut-off shall beremoved when green Chipping of concreteis not to be permitted.

Length of Tremmie pipe shall be reducedby removal of Tremmie segment stage bystage.

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Withdrawal of Stop ends

Withdrawal of Stop ends just after theInitial setting of concrete.

If retarders are not added, Stop End Pipesshall be moved up & down not later than45 minutes from the time of placing ofconcrete.

Contact Details

Gagan Goswami Cell-+919662506595Address- HERITAGE INFRASPACE INDIA PVT. LTD F-36,Sukh Shine, Opposite to Himalaya Mall Drive In Road, Ahmadabad, Gujarat ,India

E mail- info@diaphragmwallconstruction.com,gagangoswami@yahoo.co.in

Website- www.diaphragmwallconstruction.com

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