Investigation of Dynamic Fragmentation Mechanism of Granular Column Collapse Via Discrete Element Analyses

This paper investigates the dynamic fragmentation mechanism of granular column collapse, which is applicable to the real columnar rockfall. A series of numerical simulations by discrete element method (DEM) were performed for a simple granular column with different aspect ratios, where bonds within the bottom 20% height of the column are broken as the trigger for model failure. Firstly, the surface morphology and the nominal runout distance for different aspect ratio of the granular column have been analyzed. The result shows that the surface deformation of the granular column with a large aspect ratio (larger than three) is much more obvious than that with a small aspect ratio, and the nominal runout distance is positively correlated with the aspect ratio. The velocity and fragmentation evolution results indicate that the dynamic process of the granular column shows a pattern of bottom-crashing–falling–flow accumulation, and the fragmentation is mainly caused by the bottom-compression and the collision during the fall. The cumulative fragment size distributions fitting results indicate that the fragments fractal dimension \(D\) increases (1.62–1.88) and the fragments scale parameter \({d}_{c}\) decreases significantly (0.07–0.04) before and after the collapse, which suggests that the granular column underwent significant fragmentation and produced a lot of fine fragments during the collapse. The comprehensive performance of granular columns with different bond strengths indicates that the dynamical behavior, fragmentation, and accumulation morphology of granular columns collapse are all affected by the bond strength. The research results are a valuable inspiration for the study of real rockfall cases.