Influence of Weak Layer Heterogeneity on Slab Avalanche Release Using a Finite Element Method

Abstract

Snow avalanches generally result from the collapse of a weak layer underlaying a cohesive slab. We use the finite element code Cast3m to build a complete mechanical model of the {weak layer-slab} system including inertial effects. We model the weak layer as a strain-softening interface whose properties are spatially heterogeneous. The softening accounts for the breaking of ice bridges. The overlying slab is represented by a Drucker-Prager elasto-plastic model, with post-peak softening to model the crack opening. The two key ingredients for the mechanical description of avalanches releases are the heterogeneity of the weak layer and the redistribution of stresses by elasticity of the slab. The heterogeneity is modeled through a Gaussian stochastic distribution of the friction angle with spatial correlations. We first study the effect of the weak layer’s heterogeneity and the slab depth on the release on a simple uniform slope geometry. We observe two releases types, full slope releases corresponding to a crown rupture and partial slope releases for which the traction rupture occurs inside the slope and thus only a part of the slope is released. The influence of slab depth on the relative proportion of these two rupture types, as well as on the avalanche angle distributions is also studied.