3D Numerical modeling of compressible and cohesive granular flow impact on narrow obstacles

Assessing the impact of natural granular flows, such as landslides, debris flows, and snow avalanches, on obstacles is a critical component of natural hazard mitigation. In this context, conventional approaches, which are often based on simplified analytical frameworks, are increasingly complemented by numerical methods to better capture the complex rheology of these flows. However, widely applied methods like the discrete element method are computationally intensive and struggle to represent highly compressible materials such as loose soil or snow. This study addresses this gap by employing a three-dimensional model based on the Material Point Method (MPM) and a large-strain elastoplastic framework to investigate how plastic compressibility affects the generation of impact pressure of compressible and cohesive granular flows on narrow obstacles. We conduct a comprehensive numerical study, systematically varying flow velocity, internal friction, cohesion, and plastic compressibility. Our results show that at low to moderate velocities, plastic compaction reduces impact pressure through energy dissipation. At higher velocities and for low-strength materials, however, this effect reverses, and compaction can increase impact pressure due to delayed deceleration and preservation of kinetic energy, associated with shock formation. Notably, conventional dimensionless numbers used for flow classification such as the Froude or Mach number do not consistently delineate this regime transition. These insights advance our understanding of granular impact dynamics and underscore the value of physically grounded three-dimensional continuum models for improving predictive capabilities and risk assessment in natural hazard scenarios involving highly compressible granular flows.