Stability analysis for rainfall-infiltrated unsaturated soil slopes subjected to tensile–shear failure following a nonlinear strength criterion

Rainfall infiltration is one of the major causes of slope instability. While shear failures were commonly adopted, unsaturated soil slopes are in fact highly susceptible to composite tensile-and-shear failure. To address this problem, a nonlinear Mohr–Coulomb (MC) criterion was modified to capture the time dependent tensile and shear strengths for various soils during rainfall, where the coupled effect between capillary and adsorption pressures in the soils was considered. The results showed that the proportion of adsorption stress in the total suction stress varied greatly across different soil types, with the transitional and saturated gravimetric water contents being the two most sensitive parameters affecting the proportion of adsorption stress. On this basis, energy balance equation was established through a two-stage composite tensile–shear failure mechanism of three-dimensional (3D ) slopes following the modified MC criterion. Based on the upper bound theorem of limit analysis, the factor of safety (FoS) for the slopes was calculated by incorporating the strength reduction technique to systematically investigate the effects of rainfall patterns including intensity and duration and soil types on slope stability. Comparisons by analytical and numerical approaches were conducted to verify the present work. Parametric analysis revealed that a 3D analysis could better reflect the slope stability, and that the falling range of slope FoS was strongly correlated with the rainfall patterns and soil permeability. The present study provides a reference and method for assess the stability of various unsaturated soil slopes under different rainfall conditions.