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 model to calculate the tensile and shear strengths in low and regular stress ranges for various soils was developed, where the coupled effect between capillary and adsorption pressures in the soils was considered. The results showed that the transitional and saturated gravimetric water contents are the two most sensitive parameters affecting the proportion of adsorption stress. Thereafter, energy balance equation was established through a two-stage composite tensile-shear failure mechanism of three-dimensional (3D) slopes based on the upper bound theorem of limit analysis. The factor of safety (FoS) 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. 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 calculating the stability of various unsaturated soil slopes under different rainfall conditions.