Debris-Flow Impact on Piers with Different Cross-Sectional Shapes

We report findings from three-dimensional computational modeling and flume experiments on debris-flow impact force on piers with different shapes. The computational model captures the free surface with a volume-of-fluid method and the nonNewtonian fluid behavior with a calibrated Bingham model. The flume experiments were carried out within a customized system where a fixed volume of debris flow can be instantaneously released. Two debris flows (viscous and dilute) and two pier shapes (round and square) were tested in experiments, and the impact forces on piers were recorded. After extensive calibration using flume experiment results, the computational model was utilized to simulate conditions covering more parameter space where the release volume was increased, and three more common pier shapes (round-end, rectangle, and diamond) were simulated. In general, simulation results show that pier shape controls the runup, flow separation along the side, and the resulted force. The runups before piers with round, round-end, and diamond shapes are almost the same. However, they are smaller than those with square and rectangular shapes. For dilute debris flow, significant fluctuations exist in flow height, velocities, and impact forces due to the wavelike features. The influence of debris-flow types and pier shapes is quantified with drag coefficient. Simulation results also reveal a distinctive three-layer structure in the distribution of impact force in all cases.