Numerical analysis of slope stability in granite residual soil under rainfall conditions

Abstract Rainfall‐induced landslides in granite weathering crusts are a prevalent geological hazard in South China, yet the role of soil configuration in controlling hydromechanical responses remains insufficiently quantified. This study combines laboratory testing with fully coupled ABAQUS finite‐element simulations to examine seepage–deformation coupling and stability evolution for typical slope configurations. Direct‐shear tests show that the red soil is highly sensitive to moisture, with marked reductions in both cohesion and internal friction angle, whereas the sandy soil exhibits strength decay dominated by cohesion loss while its friction angle remains comparatively stable. Numerical results indicate that pore water pressure evolution—a key failure precursor—is primarily governed by rainfall intensity, slope position, and soil permeability, and that the slope toe saturates first and can transition to positive pressure, making it the most likely initiation zone. Distinct failure modes emerge across configurations: homogeneous red soil slopes tend to fail by sudden deep‐seated sliding triggered by localized pore pressure surges; homogeneous sandy soil slopes develop progressive toe‐initiated flow failure driven by seepage erosion; and composite slopes (red soil over sandy soil) are prone to stepped interfacial sliding due to hydro‐shear concentration across permeability contrasts. Heavy rainfall (≥0.03 m/h) and steep slopes (≥45°) substantially reduce the factor of safety. Reinforcement simulations further demonstrate that deep anchorage increases stability far more effectively than shallow root reinforcement. These findings clarify configuration‐controlled failure mechanisms and hydraulic triggering criteria, and provide a basis for early warning indicators and targeted mitigation in granite weathering crusts.