Numerical modelling of rainfall-induced shallow deformation of unsaturated soil slopes

Rainfall-induced shallow deformation of unsaturated soil slopes is a common geological hazard in hilly areas, significantly affecting engineering safety. While existing research has primarily focused on the mechanisms of rainfall-induced slope failure, systematic analysis of the deformation evolution remains insufficient. This study establishes a finite element model that couples rainfall infiltration, suction, and deformation based on unsaturated porous media consolidation theory and the Barcelona Basic Model (BBM) constitutive model, with its reliability verified against existing laboratory test results. On this basis, the shallow deformation response under different rainfall intensities and slope angles is systematically investigated. The results indicate that gentle slopes undergo continuous acceleration in deformation before stabilizing, with the final displacement increasing as rainfall intensity increases. This is attributed to the greaten infiltration under heavy rainfall, which leads to increased degree of saturation, reduced suction, and consequently aggravated deformation during the stabilization phase. In contrast, steep slopes experience continuous acceleration until failure, with higher rainfall intensity shortening the time to failure and reducing the critical displacement. Intense rainfall promotes the migration of the wetting front towards shallower depths in steep slopes, accelerating the saturation of the slip zone, thereby shortening the failure time and increasing the abruptness of deformation.