Mobility of cohesive granular flows over erodible beds: insights from discrete element simulations

Abstract

Gravitational mass movements represent a serious threat for populations and infrastructures. Their dynamics are influenced by topography, mechanical and rheological properties of the flowing material, and the potential erosion or entrainment of bed material. A longstanding challenge involves theorizing the complex influence of material rheology and entrainment on avalanche mobility to improve predictions of flow run-out and impact, crucial for hazard assessment. To enhance process understanding and improve snow avalanche physics-based models, we investigate the interplay between cohesion and entrainment on the mobility of cohesive granular flows over an erodible bed. We conducted 2D DEM simulations of an avalanche slope where cohesive granular materials release and flow over continuous erodible beds of bonded particles. A comprehensive sensitivity analysis focused on the influence of released mass, cohesion, and maximum erodible depth on avalanche mobility and entrainment rate. Our results indicate that inter-particle cohesion significantly influences flow mobility, with highly cohesive beds exhibiting limited entrainment rates and run-out distances. The study reveals that the propensity of particles to form new cohesive bonds during flow significantly affects mobility. Instances where bond formation is feasible (adhesive) show considerably lower mobility and entrained mass compared to scenarios where bonds cannot form during flow (non-adhesive). Finally, we propose a scaling law relating the ratio between actual and maximum entrainment rates to the ratio between bed cohesion and a pressure term accounting for dynamic and gravitational contributions. This study enhances our understanding of geophysical mass flow dynamics and highlights the crucial role of cohesion and entrainment in flow mobility.

Graphical Abstract