Two-phase two-point MPM modeling of submarine granular flows considering solid-to-fluid phase transition over frictional plane

Abstract

Accurate modeling of submarine granular flows is critical for landslide hazard assessment. Existing numerical methods have focused on the large deformation characteristic and fluid-soil coupling in submarine landslides, but they typically neglect the soil's nonlinear solid-fluid phase transitions and proper treatment of frictional boundaries. To address these gaps, this study presents a novel two-phase two-point Material Point Method (MPM) model that explicitly resolves granular solid-to-fluid phase transitions and frictional boundaries. The developed MPM framework rigorously couples soil and water using two sets of Lagrangian material points, effectively capturing complex soil-water interactions. For the first time, an elastoplastic-μ(I) phase transition model is implemented within the two-phase two-point MPM to account for granular phase transitions from solid-like to fluid-like states. Moreover, a frictional contact algorithm is incorporated into MPM to represent the frictional boundary. To validate the proposed method's effectiveness in simulating submarine granular flows, three benchmark examples were analyzed, including a one-dimensional consolidation problem with analytical solutions and two experimental submerged landslide cases. The simulation results exhibit remarkable consistency with analytical solutions and experimental results, validating the model's effectiveness. In particular, the study compares the elastoplastic-μ(I) phase transition model and purely solid-like elastoplastic model, and evaluates the effects of frictional boundaries on submarine landslides using the proposed MPM model. The numerical results find that: (i) the purely elastoplastic model tends to overestimate landslide runout compared to the elastoplastic-μ(I) model; (ii) increasing basal friction not only significantly reduces soil runout but also suppresses fluid vortices, thereby weakening waves in the soil-water interaction system.