Tanmoy Das

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.

Seismic performance of reinforced concrete (RC) structures is strongly influenced by soil–structure interaction (SSI), the effects of which depend on soil properties, foundation flexibility, and seismic input characteristics. This study investigates the seismic response and vulnerability of a five-story RC frame structure by explicitly considering SSI under seismic loading conditions. A three-dimensional numerical model is developed in PLAXIS3D to simulate the interaction between the structure and underlying dense sand and soft clay soils. The influence of SSI on lateral displacements, interstory drifts, and seismic fragility is evaluated. The Mohr–Coulomb (MC) model is adopted for clayey soils, while the Hardening Soil model with small-strain stiffness (HSS) is employed for sandy soils, with results indicating that the HSS model more accurately captures the seismic response of sandy deposits. For the soil profiles and structural configuration considered, the results indicate that SSI may lead to increased lateral displacements and interstory drifts, particularly in the presence of soft clay soils and flexible foundation conditions. Fragility curves are developed to quantify structural vulnerability under both near-fault and far-field ground motions. The findings show that the combined effects of SSI and near-fault seismic characteristics increase the probability of exceeding damage states at lower peak ground acceleration (PGA) levels for the studied system. These results highlight that the influence of SSI on seismic response is scenario-dependent and emphasize the importance of incorporating site-specific soil conditions and realistic soil–structure interaction modeling in performance-based seismic design and vulnerability assessment.