INDIRA SAGAR COFFER DAM PROJECT (M.P.) INDIA

DESIGN AND CONSTRUCTION OF 24M HIGH COFFER-DAM ON NARMADA RIVER FOR INDIRA SAGAR PROJECT (M.P) INDIA

This project consisted the design and construction of upstream and downstream Coffer Dam for the Indira Sagar Project. This was a new concept design where for the first time across all countries, a Coffer Dam was constructed using 5 tons pre-cast blocks as the shuttering for both upstream and downstream of the dam, and the enclosure was filled with boulders and stone-crete, underwater. All the work for the cofferdam was done under the ground and the water. The maximum height of the u/s cofferdam was 24 m, 12m under the water and 12m above the water. For the underwater portion, 5 tons of hollow pre-cast c.c. blocks were placed on the u/s and d/s side of the dam, with the help of divers. Before placing the blocks, the river bed was levelled by blasting underwater and with the use of a special technique, the PC blocks were placed. Bounders were filled in an enclosure of a 15m long cell and grout pipes with safety reinforcements were placed. The 15 m cell was thoroughly caulked from outside so that the river flow has no effect on the cell. A colloidal grout made out of sand, cement, water and superplasticizer was pumped through the grout pipe from the bottom so that the level of grout slowly built upward. Thus the colloidal grout (colcrete) replaced the water in the voids of the boulder and converted the bounder mass into concrete. About six pre-fabricated construction sluices of 2 x 3 m were placed to take care of the post-monsoon discharges up to 300 cumecs, as the diversion tunnel was under construction and was not ready.

Stonemasonry was constructed above water level over the underwater work.

The entire work of the u/s and d/s cofferdam was completed on schedule, in three working seasons, using a big contingent of cranes, underwater divers, pontoons, winches and a big team of specialized skilled workers.