SEEPAGE, SLOPE STABILITY AND EARTHQUAKE ANALYSIS OF EARTHEN DAM USING FEM SOFTWARE (ON RIBB EARTHEN DAM)

Abstract

Slope, Seepage and earthquake stability are a matter of remarkable concern in construction of earthen dams where the failure of slopes may incur severe loss of life and damage to property. The most important factors that cause instability of slope and lead to failure are gravitational force, force due to seepage of water, sudden lowering of water adjacent to a slope and force due to earthquake. This study aims at analyzing the static and dynamic slope stability of Ribb Dam using the finite element method. The analyses were carried out using “PLAXIS 2D V8.2” software employing the Mohr Coulomb elasto plastic constitutive model to define the mechanical behaviors of the dam materials. The safety factor values, Quantity of Seepage through the main body of the dam and foundation, displacements, time versus acceleration, velocity and displacements and stress-strain conditions were carried out at different critical loading conditions. The analyses were done in seven stages of construction. Peak ground acceleration (PGA) for the dynamic analyses of “PLAXIS 2D V8.2” was obtained from a real accelerogram of an earthquake recorded on February12th , 1845 around Ribb (epicenter distance of 175km) having magnitude of 6.5 Richter scale. Since the Ribb dam site and reservoir area lie on zone of VI (with magnitude of 6.5 to 4.5),analysis for an earthquake having magnitude of 4.5 has also been carried out. The results from these two values of PGA showed that, the stability analysis at all critical conditions are stable (FOS>1). Even though the condition is uncommon to occur, when the earthquake with magnitude of 6.5 and rapid draw down conditions are assumed to happen at the same time, the factor of safety is found about 0.996. The plastic stress points of all analysis shows that the boundary condition considered was acceptable and deformation analyses also show that all displacements in the dam crest are within a permissible limit.