Modelling Rapid Landslides of an Unsaturated Slope with Material Point Method: Numerical Analyses Based on a Slope Physical Model Test

Weather-induced rapid flow landslides in partially saturated soils are a topic of significant scientific interest in geotechnical engineering. The complexity of these phenomena lies in the multiphase nature of the soil (hydro-mechanical coupling) and the large post-failure displacements, which are difficult to simulate using standard numerical approaches. This study presents some numerical analyses aimed at investigating the behaviour of a slope made up of pyroclastic soil, under partially saturated conditions, moistened up to failure, replicating an experiment conducted on a slope physical model. The soil in the model, an inclined metal box, was reconstituted by pluvial deposition and then exposed to a continuous artificial rainfall until the collapse was attained. The soil was instrumented with tensio-inclinometers and targets for surface displacement measurements to monitor the evolution of the collapse process induced by the artificial rainfall. To simulate the movement of the landslide mass, numerical analyses were performed using the Material Point Method (MPM), implemented in the Anura3D software. These analyses were conducted using a Mohr-Coulomb constitutive model along with a Bishop effective stress principle. The numerical results have demonstrated the ability of the MPM to simulate the qualitative evolution of the failure process observed in the experiments in terms of triggering mechanism and post-failure kinematics. These preliminary investigations will be used as a reference for future, more refined analyses that will incorporate advanced constitutive models more specific to capture the hydromechanical characteristics of unsaturated soils.