Finite Element and Reliability Analyses for Slope Stability of Subansiri Lower Hydroelectric Project: A Case Study

The partly constructed and excavated power house slopes of Subansiri Lower Hydroelectric Project experienced extensive collapses through complex mode of failure. A detailed study is attempted in this paper to understand the reasons for the failure and assess the stability of the existing constructed slopes using limit equilibrium and FEM solutions and also to propose modified design for rebuilding the slopes. To take into account the uncertainty associated with the rockmass and soil properties, probability and reliability analyses have also been carried out. Based on the field observations and stability analyses of the natural and cut slopes, suitable support systems such as slope flattening with various angles, weldmesh, shotcrete, rockbolts and drainage holes have been considered to meet the stability requirements. In this study, it is demonstrated that the probabilistic approach when used in conjunction with deterministic approach helps in providing a rational solution for quantification of stability in the estimation of risk associated with the power house slope construction.