Stability Assessment of Landslides under Coupling Action of Rainfall and Earthquake

Abstract Separated analyses are widely used to evaluate the stability of slopes after rainfall and earthquakes. However, the combined impact of rainfall infiltration and earthquake shaking on slope stability remains insufficiently studied. Therefore, a unique closed-form analytical solution to calculate the factor of safety (FS) for homogeneous unsaturated slopes under combined seepage and seismic forces has been proposed by modifying the conventional Bishop’s method. The two-dimensional seepage pattern was considered to capture rainfall infiltration, while pseudo-dynamic forces at each failure slice accounted for earthquake shaking. Further, an analytical search method was developed to locate the critical slip surface. Additionally, a coupled hydromechanical finite-element model was used to analyze rainfall-induced seepage, deformation, and stress redistribution. The resulting slope condition was further evaluated under seismic loading to represent rainfall–earthquake effects without implying full two-way coupling between infiltration and earthquake shaking. All these newly proposed methodologies were applied to the 2014 Malin landslide in Maharashtra, India, to replicate the landslide mechanism and identify root causes to show the application of proposed analytical solutions. A comparison with field observations and literature demonstrated that both the analytical and numerical models realistically represented the Malin landslide. Further, the proposed analytical model was validated against a numerical analysis of a real earthquake-induced landslide. The models accurately reproduced the onset, failure zone, and progression of instability over time. The present study provides the application of new analytical solutions for practical landslides, additionally offering a reference for prevention and evacuation plans.