EFFECT OF DRAWDOWN ON TEHRI RESERVOIR RIM STABILITY AND APPLICATION OF GEO-REINFORCED SOIL STRUCTURE

Abstract

Tehri dam in Uttarakhand, India is a 260.5m high earth and rock fill dam. It is located on river Bhagirathi at nearly 1.5km downstream of the confluence of Bhilangana and Bhagirathi. A reservoir was created in the upstream valley as a result of the dam's construction and it’s creating a dead storage of 925 Mm3 and live storage of 2,615 Mm3 water, making a total storage capacity of 3,540 Mm3. During drawdown circumstances, the reservoir water oscillates between the dead storage level (DSL) and the maximum reservoir level (MRL). The valley slopes below the water level in the reservoir periphery are submerged when the water level reaches MRL. Although the weight of the rocks decreases, the lateral force of the standing water prevents the slope's inclination to slide. Significant drawdowns result in an increase in the slope material's weight just above the water line and a decrease in shear strength, which leads to optimal conditions for slope instability. This research uses the Slope/W and Seep/W models at several sites in the Tehri reservoir rim at varying water levels to verify the slope stability using GIS software. Each analysis has been performed with actual slope profile surrounding the reservoir. Two geo reinforcement models i.e. soil nails and concrete structures have been analyzed to enhance the stability of slope by using Geo-Studio software. A comparison of results of all the techniques is carried out to find the most effective technique to enhance the slope stability.