SEEPAGE AND STABILITY ANALYSES OF EARTHEN DAMS

Abstract

The present study is concerned with the seepage and stability analysis ofearth dams. Avariably saturated numerical flow model is developed for the seepage analysis. The model is based on fully implicit finite difference numerical scheme. The model also accounts for the heterogeneity due to the presence of core and drain. The variably saturated flow model developed for simulating the pore water pressure/ soil moisture content distributions is validated employing an analytical solution (Harr, 1962) and a reported data set (Giu et al. 2000). The model computed pore water pressure is used in the stability analysis of upstream and downstream slopes. The stability analysis is carried out using modified Bishop's method. Dynamic analysis ofslope stability is conducted using pseudostatic analysis. The numerical model is applied to analyse the transient seepage and stability analysis under reservoir filling and sudden drawdown condition. Under reservoir filling condition, the factor of safety of downstream slope is evaluated while the factor of safety of upstream slope evaluated under sudden drawdown condition. A detailed sensitivity analysis is performed to study the effect of hydraulic parameters such as saturated hydraulic conductivity, unsaturated soil parameters and anisotropy on transient seepage and stability analysis of homogeneous dam. It is observed that the hydraulic parameters have significant influence on transient seepage pore water pressure distribution and associated slope stability. However, their effect becomes insignificant once the system attains steady state. Seismic effects considerably reduce the factor of safety of both upstream and downstream slopes. Themodel is also applied to study the effect of core on the seepage and stability of an earth dam with a central core. The sensitivity analysis indicates that the saturated hydraulic conductivity of the core material plays a dominant role on the seepage and n slope stability as compared to other hydraulic parameters. Seismic effects considerably reduce the factors of safety of both upstream and downstream slopes. For eight specific situations which arise due to consideration of homogeneous versus core dam, static versus dynamic effects, and reservoir full versus sudden drawdown conditions, ANN models are developed for evaluating factor of safety. in