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.
  • 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.
  • Joints of adjacent panels to be cleaned to obtain watertight bond.
  • Loose materials to be lifted by suitable air lifting method.
  • Excavation of panel is followed by placing of steel reinforcement cage in center of the panel.
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.
  • 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.
  • Caution – Bottom end of Tremmie pipe must remains immersed in concrete.
  • Operation to be continued till good concrete reaches 300mm above the cut-off level of Diaphragm Wall.
  • This concrete above cut-off shall be removed when green Chipping of concrete is not to be permitted.
  • Length of Tremmie pipe shall be reduced by removal of Tremmie segment stage by stage.
  • Withdrawal of Stop ends just after the Initial setting of concrete.