Experimental and numerical investigation of the granular column collapse under different initial water-saturation conditions

This paper investigates experimentally and numerically the collapse of granular columns under different initial water-saturation conditions. The results show that the collapse dynamics of water-granular mixture columns strongly depend on the initial saturation condition. With the increase of initial water content of the column, both the particle runout distance and the particle velocity increase. During the collapse, different flow regimes, e.g., water-saturated, over-saturated, under-saturated or pure granular, pure water regions, can develop. Differences in particle velocities between the upper pure granular layer and the lower mixture layer in an under-saturated mixture, and the effect of the interaction between the upper pure water layer and the lower mixture layer in an over-saturated mixture are observed in the experiments. To describe such flow behaviours, a recently developed depth-averaged model with a two-layer structure is adopted, which is able to capture the dynamics with different flow regimes simultaneously, as well as their occurrence, transition, and disappearance. Comparisons between experimental and numerical results demonstrate good agreement. Additionally, the effects of the initial solid volume fraction and the initial column aspect ratio are analysed and quantified by numerical investigations, providing further insights into the mechanisms governing the flow dynamics.