On the use of a unified constitutive model for modelling slope large deformations with material point method

Landslides and debris flows can have devastating effects, particularly when movement involves a transition from solid-like to fluid-like process. The elastoplastic constitutive model has a limited ability to describe the entire movement process; thus, this paper establishes a unified constitutive model comprising a hypoplastic model and Bagnold model within a GPU-accelerated material point method (MPM) framework. The model is validated first through low-speed direct shear tests to demonstrate its ability to describe solid-state friction behaviour, then collision behaviour under rapid flow conditions is examined using high-speed annular shear tests. The validity of the unified model for geotechnical engineering large deformations is subsequently verified using column collapse, where the superiority of the unified model over the traditional constitutive model in describing the large deformation process is demonstrated. An index, the dynamic stress ratio, is comprehensively analysed over the whole column failure process and the dynamic stress ratio is found to correlate well with the second-order work conversion criterion, distinguishing the transition of movement from solid-like to fluid-like stage. Finally, the constitutive model is applied to a hazard assessment of the Qianjiangping and Tatopani landslides in which the applicability and stability of the model along with the MPM framework are further demonstrated.