Micromechanical investigation of snow failure under mixed-mode loading

An intimate understanding of snow failure, particularly under mixed-mode shear and normal loading, is a key ingredient for numerical modelling of snow avalanche release. Due to its highly porous structure, the failure of snow can result in a volumetric collapse. Despite its importance, snow failure and collapse remain poorly understood, mainly due to the fragile nature of the material, which renders systematic experimental exploration difficult and complicates observation at the microscopic level. A microstructure-based discrete element model of snow has been developed and utilized to study snow failure under mixed-mode loading. Depending on applied normal stress, three distinct failure regimes are identified, characterized by different volumetric responses. Shear-induced macroscopic collapse is observed to develop above a critical level of normal stress. A deeper understanding of the mechanisms leading to this volumetric collapse is investigated on the microscopic scale. Force chain buckling within the snow sample leads to volumetric collapse, while stable force chains result in a localized failure and the absence of a volumetric collapse. The stability of the force chains is shown to be insured by the grain contacts between the force chains and the surrounding material. The ratio of contacts close to failure is identified to control the absence or presence of collapse after failure.