MPM-based mechanism and runout analysis of a compound reactivated landslide

Understanding the entire process of hydraulic-related landslide reactivations is crucial for risk assessment, which includes initiation and runout evolves from a small-deformation in the pre-failure stage to large-deformation after failure, with complex interactions between the materials in solid and liquid phases. This paper reproduces the entire process of a reactivated landslide using Material Point Method (MPM). The accuracy of MPM is validated in comparison to Limit Equilibrium Method (LEM) and Finite Element Method (FEM). The effects of antecedent rainfall and pre-existing groundwater on landslide runout and the deposits morphology are discussed. Results show that the antecedent rainwater rises the groundwater level and saturates the front edge of slope where the initial failure occurred. Three computed spatio-temporal distributions of pore water pressure show good agreement and match well with field evidence. The kinematic characteristics show that the landslide has different moving features with different microtopography, which reveals retrogressive failure in front and middle part of slope initially and compound retro- and pro-gressive failures occur at the rear edge. The results of unsaturated two-phase MPM are in better agreement with the measured morphology than full-saturated MPM. The antecedent rainfall and the pre-existing groundwater are the main contributing factors to the landslide runout.