Exploring the relative contributions of fluid and solid phases in debris flow barrier impact

Landslide barrier structures constructed on high-risk slopes are a useful strategy to halt and retain debris to protect vulnerable downslope infrastructure and inhabitations. To appropriately design these systems, an estimate of the likely volume, thickness, and velocity of the flow is required immediately prior to interaction with the barrier. These characteristics of the flow, when combined with an analytical model or numerical simulation of the impact, define the structural demand on the barrier. In this study, we use the large Queen’s University Landslide Flume to explore the relative contributions of the fluid and solid phases of a multi-phase flow on the structural demand on a barrier. Impact forces following dam break experiments of up to 1 m³ of material, released from the top of a 6.5 m long slope inclined at 30 degrees are explored for releases of pure water, dry granular particles, and fully-saturated granular water-grain mixtures. Impacting the barrier at approximately 4-5 m/s, temporal impact behaviour captured using ultrahigh speed imaging is correlated with the time series of impact load. Quantitative comparisons are then made between the observations of impact force by each class of flow to predictive equations published in the literature, highlighting the degree of match, hypotheses for observed discrepancies, and the relative contributions of the fluid and solid phases.