41 Micromechanical modeling of crack propagation in weak snow layer

Bobillier Grégoire1, van Herwijnen Alec1, Bergfeld Bastian1, Gaume Johan2, Schweizer Jürg1

  1. WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
  2. SLAB Snow and Avalanche Simulation Laboratory, EPFL Swiss Federal Institute of Technology, Lausanne, Switzerland

Improving the prediction of snow avalanches requires a detailed understanding of the fracture behavior of snow, which is intimately linked to the mechanical properties of the snow layers (strength, elasticity of the weak and slab layer). While the basic concepts of avalanche release are relatively well understood, understanding crack propagation propensity remains a great challenge, which can be tackled with numerical modeling or field measurements. In the field, the propagation saw test (PST), a fracture mechanical field experiment, provides information on crack propagation propensity in weak snowpack layers. It has become a valuable research tool to investigate processes and mechanical parameters involved in crack propagation.

Here, we follow the numerical approach by using the discrete element method (DEM) to numerically simulate a PST and analyze the fracture dynamics. With DEM we can mimic the snow microstructure in simplified form and numerically reproduce the two basic layers required for a dry-snow slab avalanche: a highly porous and brittle weak layer covered by a dense cohesive slab.

The results of these numerical PTSs reproduce the main dynamics of crack propagation observed in the field. We developed different metrics to define the crack tip that allow deriving the crack velocity. Our results show that crack propagation on flat terrain reaches a stationary velocity if the snow column is long enough. The length of the snow column to reach stationary crack velocity depends on snowpack parameters. On sloped terrain, we observe a transition in the local failure mode that can be visualized based on the crack tip morphology and the main stress component.

Our findings lay the foundation for a comprehensive study on the influence of snowpack properties on these fundamental processes for avalanche release.