Erosion Mechanisms of Landslides: Granular Column Collapse Experiment on Erodible Beds and DEM Insights

Abstract

Dynamic erosion and entrainment of loose path materials can fundamentally reshape the mobility, kinematic stages, and deposition morphology of rapid granular landslides. However, it remains challenging to isolate controlling factors because erosion results from coupled momentum transfer, bed deformation, and local mass exchange at the particle scale. This paper investigates erosion development during granular column collapse over erodible beds through laboratory experiments and three-dimensional discrete element method (DEM) simulations. A transparent flume (120 cm long, 80 cm high, 20 cm wide) was used to release granular columns onto a 5 cm-thick erodible layer, enabling systematic comparisons across material combinations and initial aspect ratios while minimizing wall effects by ensuring a sufficiently large flume-width-to-particle-size ratio. Experiments were repeated three times for each condition to ensure reproducibility. Three distinct regimes were identified from synchronized observations of free-surface evolution, erosion-interface migration, and front kinematics: (i) non-erosion, (ii) overriding (covering) erosion, and (iii) plunging (penetrating) erosion. Front-position evolution exhibits a characteristic S-shaped trajectory with acceleration, quasi-steady propagation, and deceleration stages. Erosion significantly prolongs the initial acceleration and final deceleration stages while shortening the quasi-steady stage, yet the total flow duration remains proportional to the free-fall timescale. DEM results reproduce these trends and reveal that the particle density ratio between the column and bed governs regime transitions, whereas particle size ratio and initial aspect ratio play secondary roles.