Smoothed particle hydrodynamics (SPH) modelling for rainfall-induced unsaturated slope failure considering void ratio dependence and variability

Rainfall-induced unsaturated slope failures are among the most frequent and destructive forms of landslides worldwide, often resulting in significant casualties and economic losses. Accurately predicting such failures requires not only a robust numerical approach that captures the coupled hydraulic and mechanical behaviours of unsaturated soils, but also a thorough understanding of how spatial variability of soil properties influences slope stability. In this study, smoothed particle hydrodynamics (SPH) is employed in conjunction with an advanced unsaturated constitutive model to investigate, for the first time, the effects of void ratio dependence and variability on rainfall-induced unsaturated slope failure. The model captures the coupled hydro-mechanical behaviour of unsaturated soils, accounting for the influence of void ratio on water retention, infiltration and strength characteristics. A single-layer multiphase SPH approach is employed, where each particle simultaneously represents the water, air, and solid phases, enabling the efficient and robust simulation of large-deformation problems. The SPH model is applied to a synthetic slope with spatial variable soil properties to explore how heterogeneity in void ratio alters failure mechanisms and onset conditions. The results provide new insights into the role of void ratio heterogeneity in rainfall-triggered landslides and demonstrate the potential of advanced SPH modelling for practical probabilistic analysis in geotechnical applications.