Influence of earthquake-induced pore-water pressure on the seismic stability of cohesive slopes

In the seismic stability analysis of natural slopes the possibly occurring weakening effects due to excess pore-water pressures and cyclic degradation are generally neglected or not properly accounted for. Accordingly, the evaluation of the seismic performance of a slope may result unreliable. The paper describes a simplified procedure for the evaluation of the seismic stability conditions of clay slopes taking into account the possible occurrence of cyclic strength degradation due to excess pore water pressures. An experimental-based model was adopted to predict the occurrence and the magnitude of the excess pore-water pressure, starting from an assessment of the earthquake-induced shear strain level. The results of the numerical analyses presented in the paper show that the amplitude of the horizontal acceleration and the plasticity of the soil are the main responsible of the occurrence of weakening and inertial-weakening instabilities.