This was challenging work of design and construction of coffer dams (u/s and d/s.) in coarse sand in the river bed. In post monsoon period, though there remains very little surface flow in the river, but ipso-facto entire river flows through the coarse sand bed. Hence RCC diaphragm wall was designed to cut off the flow through the sand bed and also to divert the surface flow in the diversion channel.
60 cm thick RCC diaphragm wall has been constructed and used as cut off as well as coffer dams on u/s and d/s side of main dam. Wherever depth of diaphragm wall was less than 10 M post tension anchors of capacity 135 Tones to 170 tons at an inclination of 45 degrees, through the diaphragm wall and sand bed were provided. Reaction was taken from the base rock in which tendons were grouted and were locked on the u/s face of diaphragm wall. Post tension anchors were necessary because of moving sand bed during the monsoon flood in the river bed.
Wherever depth of diaphragm wall was more then 10 M, post tension anchors were not feasible and T- shape RCC diaphragm was design and constructed on the principle of counter fort walls.
The entire work involved 12000 sq mtr of diaphragm wall with 500 numbers of post tension anchors, which has been completed in two working season, in most trying and difficult climatic conditions (max. temp 49 degree C). A big contingent of cranes, hydraulic excavators, dumpers, winches, heavy chisel with highly skilled special labours were mobilized to complete the work in time.