Procedure

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.

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