(Journal Navnirman, July-December 2003, pp. 6).
The obligatory excavations done for the lower chute of auxiliary spillway and for the foundations of stilling basin (Bay No. 1) of service spillway have resulted into 23 to 43 m high transverse cut face in the downstream of block No. 28. This cut face is lined as a concrete cladding wall. Due to various reasons, the actual slope of the excavated cut face became flatter than 8(V): 1(H) adopted slope in design resulted in an inverted trapezoidal section at upper level. Along the cut face, undesired features like semi-detached rock mass, overhangs, opening along joints, fault, red bole layer etc. were noticed. During the heavy flood of 1994, the weak and weathered rock mass along with the part of the wall foundation beyond 170 m down stream was eroded. The paper gives the geological details of cut face conditions, modifications in design for the stability of wall as per actual site conditions, treatment provided to weak features, open jointed rock mass etc.
Obligatory excavations, Auxiliary spillway, Foundations, Stilling basin, Semi-detached rock mass, Opening along joints, fault, red bole layer, Weak and weathered rockmass, Geological details, Modifications in design
