This study presents a novel two-phase, two-point hydro-mechanical coupled Material Point Method (MPM) framework to simulate the full-process, infiltration-induced failure of unsaturated soil slopes. By incorporating a dual-layer material point scheme, moisture-dependent yield stress, void ratio-dependent hydraulic function, and shear-induced strain-softening laws, the framework effectively captures solid-fluid interaction and progressive softening of metastable soil structures. The proposed method is validated against element tests and physical model tests, and subsequently applied to two representative case studies: rainfall-triggered failure in a loose-fill slope (1976 Sau Mau Ping landslide) and irrigation-induced collapse in a loess slope (2015 Jiaojiayan South landslide). Numerical results demonstrate the capability of the developed code in capturing suction loss, excess pore water pressure generation, and the transition from local failure to long-runout flowsliding. The case studies reveal that strain softening plays a critical role in controlling shear band localization and runout dynamics in both metastable slopes. This advanced numerical tool provides enhanced predictive capability for unsaturated slope hazard assessment.

landslides;Partial saturation;Numerical modelling;Hydro-mechanical coupling;Runout