90. Cautious Excavation and Foundation Treatment for Turbine Units of Underground River Bed Power House, Sardar Sarovar (Narmada) Project

The underground power house at Sardar Sarovar (Narmada) Project is in advanced construction stage. The power house is situated on right bank of river and 157.5 in the downstream of toe of Main Dam. It will house six reversible units for generating 1200 MW power. The excavation for the cavern of underground power house was suspended in1993 due to distressing in both upstream and downstream walls. After completion of treatment for strengthening the walls, the remaining excavation for the cavern and turbine units was resumed in April 1999. The turbine pits are surrounded by other underground openings leaving thin rock ledges between each other. In view of this and already distressed rock mass in the side walls, the excavation for the turbine pit had to be done with utmost care. At present, the excavation of pits for all six turbines have been completed and the installation of units 1 to 4 is in progress. The paper gives the details of rock mass characteristics, design parameters, support system, precautionary measures taken for the cut faces of turbine pits and treatment provided to the foundation of turbine pits.