Tehri Hydro Development Corporation Ltd.
The outlet area of tailrace tunnels is located on the left bank of river Bhagirathi in the downstream of Tehri dam, The slopes in this area were occupied by overburdened slide mass with scanty exposure of weathered phylitic quartzite. Stabilization of slopes at lower levels was required to construct the outlet works and to maintain access to the portals for TRT-1 and TRT-2. To do the construction works simultaneously with the slope stabilization works was a challenging task. One option that considered was a cut and cover tunnel to accommodate the access road to the tailrace portals and the placement of backfi ll to buttress the toe of the slope. Emphasis was given to keep the toe of the slope as free draining material and effective drainage arrangements.Stabilization works were therefore undertaken which consisted of buttress berm, cellular toe walls, effective surface as well as subsurface drainage arrangements.
This paper describes the slope stability analysis, remedial measures adopted to arrest movement of the unstable slopes in the area of tailrace tunnel outlet works and the method of construction of tailrace portals without causing any instability to hill slopes, monitoring the behaviour of slope and the retaining cellular structures etc.
