Mechanisms of particle-induced landslide propagation and flood-driven transport: Insight from volume-of-fluid and discrete element method coupled simulations

This study delves into the effects of particle morphology (spherical, tetrahedral, and cubic) and size on the motion characteristics of particles during landslides and water erosion processes, using coupled Volume-of-Fluid and Discrete Element Method simulations. Simulation results reveal a positive correlation between particle sliding distance and its diameter, whereas angular velocity decreases as diameter increases. Spherical particles, due to their symmetrical shape, exhibit the highest mobility and readily form continuous flow layers. In contrast, tetrahedral and cubic particles display more complex motion patterns and are unevenly distributed within the landslide mass. Furthermore, as particle morphology shifts from spherical to tetrahedral and cubic, the critical initiation velocity for hydraulic transport gradually increases (from 9.6 to 13.6 m s−1 and 15.5 m s−1, respectively), highlighting the significant impact of morphology on particle initiation conditions. Different particle morphologies also lead to variations in hydrodynamic characteristics; spherical particles tend to form stable flow structures, whereas tetrahedral and cubic particles may generate more complex turbulence. Based on these findings, we propose a simplified empirical framework in which the critical initiation velocity scales as a power-law function of a quantified shape factor and particle size. This relationship provides a practical basis for estimating the hydraulic initiation thresholds of irregular particles in channel deposits and can support the assessment of debris-flow risks in steep mountainous regions.