Decoupling the role of inertia, friction and cohesion in dense granular avalanche pressure build‐up on obstacles

Understanding the physical processes involved in snow avalanche‐obstacle interaction is essential to be able to estimate the pressure exerted on structures. Although avalanche impact pressure has been measured in field experiments for decades, the underlying physical principles are still elusive. Previous studies suggest that pressure is increased due to the formation of an influenced flow region around the structure, the mobilized domain, which varies in size depending on snow properties such as snow cohesion. Here, we aim to better understand how cohesion, friction, velocity and their interplay affect avalanche pressure build‐up on structures. This is achieved by simulating the avalanche‐obstacle interaction with a newly developed numerical model based on the Discrete Element Method, using a cohesive bond contact law. The relevance of the model is tested by comparing simulated impact pressures with field measurements from the Vallée de la Sionne experimental site. Our results show that at the macro‐scale, impact pressure consists of the inertial, frictional and cohesive contributions. The inertial and frictional contributions arise due to the existence, shape and dimension of the mobilized domain. The cohesive contribution increases the particle contact forces inside the domain, leading up to a doubling of the pressure. Based on these physical processes, we propose a novel scaling law to reduce the problem of calculating the pressure induced by cohesive flows, to the calculation of cohesion‐less flows. These findings enhance our understanding of the interaction of cohesive granular flows, such as snow avalanches, and structures at the micro and macro‐scale.