Seismic Stability Analysis of Slopes using Limit Equilibrium and Finite Element Method

Abstract

Seismic slope instability poses a major hazard in earthquake-prone regions, where ground shaking can cause sudden slope failures resulting in severe damage and loss of life. Reliable assessment of seismic slope performance is therefore essential for geotechnical design. This study compares the Limit Equilibrium Method (LEM) and the Finite Element Method (FEM) in evaluating slope stability under pseudo-static and dynamic loading. The analysis investigates the effects of horizontal (k_h) and vertical (k_v) seismic coefficients, soil constitutive models, mesh refinement, and earthquake loading types on the Factor of Safety (FoS). Pseudo-static results show a clear reduction in stability with increasing seismic intensity. As the horizontal coefficient increases from k_h=0.0 to k_h=0.20, the FoS decreases from 1.706 to 0.945 in LEM and from 2.018 to 1.123 in FEM. Vertical acceleration further reduces FoS, especially when k_v approx 0.75 k_h. FEM consistently predicts higher stability than LEM, typically by 17-19%, due to its ability to model stress redistribution and deformation compatibility. Analyses of constitutive models and mesh refinement indicate close agreement between Mohr-Coulomb and Hardening Soil Small models, with differences generally within 1-3%, while finer meshes reduce FoS by 2-7% due to improved strain localization. Dynamic simulations show that time-history loading produces slightly higher FoS than pseudo-static analysis, whereas harmonic cyclic loading yields the lowest stability. These results highlight the importance of advanced numerical modeling and realistic seismic input in achieving reliable assessments of seismic slope stability.