Construction of Diaphragm Wall Presentation by: Gagan Goswami 1
Content Introduction Application Category of Diaphragm Wall Construction Procedure 2
Introduction Diaphragm Wall is generally reinforced concrete wall constructed in the ground using Underslurry technique which was developed in Europe. The technique involves excavating a narrow trench that is kept full of an engineered fluid of slurry. Walls of thickness between 300 and 1200 mm can be formed in this way up to a depths of 45 meters. 3
Conceptual sketch showing the RCC Diaphragm Wall 4
Diaphragm wall-Application Commonly used in congested areas -Can be Installed in close proximity to existing structure Practically suited for deep basements Used in conjunction with “Top Down” construction technique 5
Schematic section of Diaphragm Wall showing typical use 6
Schematic section of Diaphragm Wall showing typical use 7
Schematic section of Diaphragm Wall showing typical use 8
Schematic section of Diaphragm Wall showing typical use 9
Anchoring of Diaphragm Wall using Anchor Slab Anchor Slab 10
Anchoring of Diaphragm Wall using Anchor Blocks Diaphragm Wall Anchor Bars Anchor Blocks 11
Important Conditions Dictate the use of Diaphragm Wall Very unstable soil profiles below the water table Limited construction time Where deeper than normal cantilever support may be required 12
Positive facades of Diaphragm Wall 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. 13
Negative Facades of Diaphragm Wall Not economical for small, shallow Basements 14
Category of Diaphragm wall In Situ Cement Bentonite Vertical Wall 1) In Situ RCC Vertical Wall 2) Precast RCC Vertical Wall 3) 15
In Situ Cement Bentonite Vertical Wall Provides water tight barrier Used to prevent seepage/water loss from Natural reservoir and Dams 16
In Situ RCC Vertical Wall Underground Structural element Used for Retention systems and Permanent foundation walls Deep groundwater barriers 17
Procedure Diaphragm Wall construction begins with the trench being excavated in discontinuous sections or “panels”. Stop-ends are placed vertically at each end of primary panel to form joints for adjacent secondary panel or closing panels. Panels are usually 4 to 6 meters long. Stop-ends are used to form the joints between adjacent panels and a water bar can be incorporated across these joints. 18
Construction Method P rim a ry S e co n d a ry S e co n d a ry S e co n d a ry S e co n d a ry C lo sin g S e co n d a ry C o n stru ctio n Jo in t fo rm e d b y C o n stru ctio n Jo in t C ircu la r Sto p e n d P ip e S c h e m a tic D ia g ra m S h o w in g C o n stru c tio n J o in t b e tw e e n A d ju c e n t P a n e ls 19
Construction Method S e co n d a ry P rim a ry S e co n d a ry S e co n d a ry S e co n d a ry C lo sin g S e co n d a ry C o n stru ctio n Jo in t fo rm e d b y C o n stru ctio n Jo in t F la t Sto p e n d S c h e m a tic D ia gra m S h o w in g C o n stru c tio n J o in t b e tw e e n A d ju c e n t P a n e ls 20
Different Shapes of Diaphragm Wall Panel T-Shape Panel L-Shape Panel 21
Different stages of construction activities 22
Diaphragm Wall Construction Site 23
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 24
Guide Wall Construction Guide Wall is constructed to fix the alignment of Diaphragm Wall in the field 25
Guide Wall Construction 26
Trenching Equipments Hydraulic Grab Kelly-mounted or Cable-hung cam buckets 27
Kelly-mounted Hydraulic Grab 28
Cable-hung cam bucket 29
Trenching Process Trenching usually carried out under bentonite slurry Bentonite Slurry – Key component. -This Slurry acts as shoring to prevent collapse by hydraulic pressure and thyrotrophic property. 30
Bentonite Slurry Used as a support fluid The bentonite suspension used in bore holes is basically a clay of montmorillonite group having exchangeable sodium cations (Na+). The action of bentonite in stabilizing the sides of bore holes is primarily due to the thixotropic property of bentonite suspension. The bentonite suspension when undisturbed forms a jelly which when agitated becomes a fluid again. 31
Functions of Bentonite In case of granular soils, the bentonite suspension penetrates into the sides under positive pressure and after a while forms a jelly. The bentonite suspension gets deposited on the sides of the hole resulting in the formation of a filter cake in contact with soil against which the fluid pressure acts. In case of impervious clay, the bentonite does not penetrate into the soil, but deposits only a thin film on the surface of the hole. 32
Factors affecting stability of Trench Level of the supporting fluid -Level of the bentonite slurry should be maintained preferably at least 1.5m above the ground water level to avoid problem of instability. Density and Viscosity of supporting fluid Loss of shear strength with time Suction effect during trenching 33
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 by Marsh cone Swelling index: Swelling index at least 2 times of dry volume. pH value : Less than 11.5 34
Tests and compliance values for support fluid prepared from bentonite (as per IS9556-1980) Property Test method As supplied Before to the bore concreting Density Mud balance 1.04- <1.15g/ml 1.10g/ml Viscosity Marsh cone 30 - 90 seconds Shear Shearometer / 1.4 to 10 strength N/sq.m Vane shear apparatus pH Digital pH meter 9.5-12 35
Schematic Diagram of Bentonite Setup •Storage tanks Settling Circulation Fresh T3 T2 T1 Mixer •Mud Pump Diaphragm Wall Construction area 36
Bentonite Setup 37
Preparation of Bentonite Slurry Bentonite slurry made by passing dry powder through water jet. A conical hopper is used with bottom nozzle through which water is pumped under pressure. The bentonite powder is poured directly from top and when it falls down the hopper, it gets agitated in the water. After getting circulated, the mixed bentonite thus falls in the tank. 38
Trench Cleaning Joints of adjacent panels to be cleaned to obtain watertight bond Loose materials to be lifted by suitable air lifting method 39
Fixing of Stop ends Stop ends to be fixed at the proper position keeping it truly vertical Distance between two Stop ends to be fixed as per prefixed Panel Layout 40
Reinforcement Cage Excavation of panel is followed by placing of steel reinforcement cage in center of the panel. 41
Reinforcement Cage fabrication 42
Reinforcement Cage shifting 43
Lowering of reinforcement cage in the excavated panel 44
Resting of reinforcement cage in the excavated panel 45
Different stages of construction 46
Placing of Concrete Placing of concrete having slump 150mm to 190mm by tremmie method Concrete to be placed through a top metal hopper and into a rigid leak proof tremmie pipe (2 sets), sufficiently large enough to permit free flow of concrete. Initially there should be a suitable plug at the bottom of metal hopper, which will not discharge concrete until sufficient concrete accumulate in the metal hopper. concrete displaces the slurry from bottom and rises in such a manner that mixing of concrete with slurry does not occurs 47
Placing Concrete 48
Placing of Concrete Pouring shall be continued till it accumulates in vertical Tremmie pipe up to top of funnel. Tremmie pipe shall be raised so as to release the concrete in a single continuous flow. Concrete to be discharged in the trench without any lateral movement of Tremmie pipe. 49
Recommend
More recommend
