Characteristics of the impact pressure of an outburst debris flow: Insights from experimental flume tests

Debris flows generated by landslide dam failures are highly destructive and can result in rapid, large-scale landscape changes. Understanding the formation and impact dynamics of an outburst debris flow is essential for effective hazard mitigation. In this study, we conducted a series of experiments to investigate the flow dynamics and the impact against an obstacle of outburst debris flows by measuring the flow properties, seismic signals, and impact forces. The results show that the impact of an outburst flow is strongly affected by the evolution of the landslide dam and the internal flow dynamics, which influence its motion and govern its rheology. For an outburst flow with a high sediment concentration caused by intensive dam erosion, the matrix structure can provide cohesive strength for the suspension of coarse particles in the flow. This significantly enhances the stationary mean impact force of the outburst flow. Furthermore, the solid inertial stress, which is a crucial factor representing particle agitation and reflecting flow properties, exhibits a positive power-law correlation with the impact force and a positive linear correlation with seismic energy. This indicates that seismic monitoring can reveal the bulk flow characteristics, internal flow dynamics and their impact characteristics. The seismic energy level increases with the velocity and bulk density of the outburst flow, while its frequency of the seismic data increases with the rate of particle impacts but decreases in the presence of a dampening layer. Our findings provide a scientific perspective for understanding the impact dynamics of an outburst debris flow that could improve the design of measures to mitigate debris-flow hazards.