Effects of retained dry material on the impact, overflow and landing dynamics

During long-term operation, the performance of obstacles would be changed due to the material accumulating upslope the obstacle. However, the effects of retained material on impact, overflow and landing dynamics of granular flow have not yet been elucidated. To address this gap, physical flume tests and discrete element simulations are conducted considering a range of normalized deposition height h0/H from 0 to 1, where h0 and H represent the deposition height and obstacle height, respectively. An analytical model is modified to evaluate the flow velocity and flow depth after interacting with the retained materials, which further serve to calculate the peak impact force on the obstacle. Notably, the computed impact forces successfully predict the experimental results when α ≥ 25°. In addition, the results indicate that a higher h0/H leads to a lower dynamic impact force, a greater landing distance L, and a larger landing coefficient Cr, where Cr is the ratio of slope-parallel component of landing velocity to flow velocity just before landing. Compared to the existing overflow model, the measured landing distance L is underestimated by up to 30%, and therefore it is insufficient for obstacle design when there is retained material. Moreover, the recommended Cr in current design practice is found to be non-conservative for estimating the landing velocity of geophysical flow. This study provides insightful scientific basis for designing obstacles with deposition.