Experimental investigation and numerical modeling of substrate erosion and entrainment in rock avalanches

Rock avalanches commonly erode and entrain loose substrate, significantly amplifying the hazard magnitude and expanding the inundation area. However, effectively simulating the runout processes while simultaneously accounting for the roles of erosion and entrainment remains a challenge. In this study, we present large-scale physical experiments on flow–substrate interaction, using a self-developed experimental apparatus. Emphasis is particularly placed on the deformation and mobilization behavior of the substrate under intensive erosive loading, which provides critical implications in developing a new erosion model. This model highlights two mechanisms. First, we incorporate the contribution of the normal stress exerted by the flow or adjacent substrate columns, which can be interpreted as a slope-parallel pressure gradient-induced longitudinal thrust acting on the substrate element. Second, the distinction between supply-unlimited and supply-limited conditions is made by identifying whether the erosion failure is distributed throughout the substrate body or localized along its base. This erosion model is then embedded into a multi-phase mass flow simulation framework, resulting in a novel approach capable of simulating the runout processes of real-world rock avalanches while explicitly accounting for the critical effects of erosion and entrainment. Finally, the proposed modeling is applied to simulate the Baige and Sedongpu rock avalanches, yielding results that closely match real observations. Further analysis reveals that erosion model-controlled entrainment spatial pattern and intensity modify the flow geometry and the rheological properties, thereby profoundly affecting flow dynamics. Our model provides a closer approximation to both experimental and field observations, particularly in capturing the dominant occurrence of substrate entrainment near the flow front.