Abstract: High-speed debris flow is commonly characterized by finite deformation, large displacement, and particle fragmentation. Using the particle discrete element method (DEM), this study simulates the size reduction of rock particles by adjusting the gradation distribution of the slide mass particles. We conduct parametric numerical simulations of a sloping site connected by a flat ground, and examine the influence of variable fragmentation factors on the movement and accumulation of non-cohesive granular assemblies. Simulations demonstrate that the difference in fragmentation degrees can induce a notable difference in the migration distance of the debris flow, and the stacking patterns of final deposits all exhibit a reverse segregation structure, while maintaining the original sequence to a certain extent. From analysis of particle velocity distribution during sliding, a dual-layer structure migration model is developed, and the simulations agree with the field observations and laboratory model tests of typical debris flow landslides. This study is most attractive for migration description of debris flows and prevention of relevant disasters.

Key words: debris flow, particle breakage, discrete element method, non-cohesive particles