BISALPUR PROJECT - UPSTREAM AND DOWNSTREAM COFFER DAMS

DESIGN AND CONSTRUCTION OF THE UPSTREAM AND DOWNSTREAM COFFER DAM BY USING AN RCC DIAPHRAGM WALL WITH POST-TENSION ANCHORS AND A T-SHAPED FRAME STRUCTURE, FOR BISALPUR PROJECT NEAR DEOLI IN RAJASTHAN, INDIA

Client: Irrigation Department, the Government of Rajasthan

Location: 6 km from Deoli town.

Usp: pioneer design concept first time in India, diaphragm wall used as cofferdams to isolate the dam construction area of water.

This was a challenging project with design and construction of cofferdams (u/s and d/s) in coarse sand of the river bed. In the post-monsoon period, though there remains very little surface flow in the river, the entire river flows through the coarse sand bed. The RCC diaphragm wall was designed to cut off the flow through the sand bed and also to divert the surface flow to the diversion channel.
A 60 cm thick RCC diaphragm wall has been constructed and used as a cut off, as well as cofferdams on the u/s and d/s side of the main dam. Wherever the depth of the diaphragm wall was less than 10 m, post-tension anchors of 135 to 170 tons of capacity, at an inclination of 45 degrees, through the diaphragm wall and sand bed were provided. The reaction was taken from the base rock where tendons were grouted and locked on the u/s face of the diaphragm wall. Post tension anchors were necessary because of the moving sand bed during the monsoon floods in the river bed.
Wherever the depth of the diaphragm wall was more than 10 metres, post-tension anchors were not feasible and a T-shaped RCC diaphragm was designed and constructed on the principle of counterfort walls.
The entire project involved 12000 sq. m of diaphragm wall and 500 post-tension anchors, which was completed in two working seasons, in the most trying and difficult climatic conditions (max. temp 49°C). A big contingent of cranes, hydraulic excavators, dumpers, winches, and heavy chisels, and a group of highly skilled special labourers were mobilized to complete the work in time.