SPH–DEM modeling of rainfall-induced slope failure in partially saturated soil–rock mixture

Abstract

Soil–rock mixture (SRM) slopes are widespread in nature, yet their numerical simulation remains challenging due to intrinsic heterogeneity and complex hydro-mechanical behavior. This study develops a multiphase coupling framework to reproduce the entire failure process of unsaturated SRM slopes, encompassing rainfall infiltration, progressive instability, and long-runout post-failure motion. The framework combines the Smoothed Particle Hydrodynamics (SPH) method, which represents soil and water using a unified particle system, with the Discrete Element Method (DEM) for explicit representation of rock blocks. An enhanced elastoplastic strain-softening model based on the Drucker–Prager criterion is implemented to capture rainfall-induced soil strength reduction, while soil–rock interaction is described by stress interpolation between SPH soil particles and DEM rock surface particles. The capability of the proposed approach is verified against a series of benchmark problems, including unsaturated soil infiltration, slope failure surface prediction, and granular flow impact tests. Comparative analyses further elucidate the distinct failure initiation mechanisms and post-failure dynamics of homogeneous versus SRM slopes under continuous rainfall infiltration. The developed SPH–DEM framework provides an effective numerical tool for investigating rainfall-induced slope failures in heterogeneous geomaterials and for evaluating associated large-deformation hazards.