Finite element analysis of coupled hydro seismic effects on rock slope stability at a tunnel portal in the Lesser Himalaya

Rock slope stability in tectonically active mountainous regions is controlled by the combined influence of structural discontinuities, groundwater conditions, and seismic loading. This study presents a comparative finite element analysis of equivalent-continuum and combined-continuum modeling approaches to evaluate the stability of a tunnel portal slope in the Lesser Himalaya under dry, groundwater, rainfall infiltration, and pseudo-static conditions. Under dry conditions, the equivalent continuum model yields a factor of safety (FoS) of 4.3 with a maximum total displacement of 0.062 m, whereas the combined continuum model, incorporating foliation joints, predicts a lower FoS of 3.34 and a higher displacement of 0.21 m. Groundwater and rainfall infiltration further reduce the FoS in both models; in the equivalent continuum model, the FoS decreases to 3.73 and 3.60, whereas in the combined continuum model, it reduces to 2.87 and 2.62, respectively. Under combined transient rainfall and pseudo-static loading, FoS decreases significantly, reaching minimum values of 2.15 and 1.41 for the equivalent and combined models, respectively. The results demonstrate that equivalent continuum models tend to overestimate slope stability by neglecting structurally controlled failure mechanisms, whereas combined continuum models provide a more realistic representation of stress concentration and deformation localization. The findings indicate that neglecting discontinuities can lead to non-conservative stability predictions under coupled hydro-mechanical and seismic loading, particularly in Himalayan rock slopes.