Snow Avalanche Simulation Laboratory

The Snow Avalanche Simulation Laboratory (SLAB) at EPFL, led by Prof. Johan Gaume, focuses on understanding and simulating gravitational mass movements, particularly snow and avalanches. Using the Material Point Method, they model large deformations, fractures, and fluid-solid behaviors to simulate the entire instability process. Their research, validated through field and lab experiments, aims to enhance risk assessment and management of alpine mass movements. SLAB's work has led to breakthroughs in modeling avalanche dynamics, snow mechanics, and glacier calving, contributing to a better understanding of snow avalanche release mechanisms and the dynamics of alpine mass movements.

Crack propagation speeds in weak snowpack layers

Johan Alexandre Philippe Gaume, Jürg Schweizer, Bertil Trottet, Grégoire Bobillier, Alec van Herwijnen

For the release of a slab avalanche, crack propagation within a weak snowpack layer below a cohesive snow slab is required. As crack speed measurements can give insight into underlying processes, we analysed three crack propagation events that occurred in similar snowpacks and covered all scales relevant for avalanche release. For the largest scale, up to 400 m, we estimated crack speed from an avalanche movie; for scales between 5 and 25 m, we used accelerometers placed on the snow surface and for scales below 5 m, we performed a propagation saw test. The mean crack speeds ranged from 36 +/- 6 to 49 +/- 5 m s(-1), and did not exhibit scale dependence. Using the discrete element method and the material point method, we reproduced the measured crack speeds reasonably well, in particular the terminal crack speed observed at smaller scales. Finally, we used a finite element model to assess the speed of different elastic waves in a layered snowpack. Results suggest that the observed cracks propagated as mixed mode closing cracks and that the flexural wave of the slab is responsible for the energy transfer to the crack tip.

CAMBRIDGE UNIV PRESS2021

Microstructure-based modeling of snow using the material point method and finite strain elastoplasticity

Johan Alexandre Philippe Gaume, Henning Löwe, Lars Kristoffer Uhlen Blatny, Stephanie Wang

The mechanical response of snow depends on its microstructural geometry. Parameters such as porosity and orientation (degree of anisotropy) are examples of microstructural parameters that can affect snow mechanical properties. Numerical simulations of snow microstructure obtained from X-ray computer tomography have aided researchers in investigating the elastic response and strength of snow. However, we lack insight into the post-peak and plastic response of snow, which in most previous studies have been oversimplified assuming (quasi-)brittle behavior. We propose studying both the elastic and post-peak behavior using the material point method (MPM), a hybrid Eulerian-Lagrangian continuum numerical method. A major advantage of MPM compared to the (classical) finite element method (FEM) is its ability to handle large deformation processes. Moreover, as a continuum method, it is significantly less computational expensive than the discrete element method (DEM). We independently study the influence of the microstructural parameters on macroscopic quantities, such as elastic modulus, strength, energy release rate and plasticity index, in mixed-mode shear-compression loading simulations. This is accomplished by using the leveled gaussian random field (GRF) approach to generate snow samples with desired microstructural properties. The ice matrix of the microstructure is modeled in the elastoplastic framework with a strain-softening Drucker-Prager failure criterion. Based on the relationships discovered through these numerical experiments, we aim to develop a microstructure-based homogenized constitutive snow model. This study will contribute to improve large-scale snow mechanical models with applications in the simulation of e.g. snow slab avalanche release, avalanche dynamics and snow-tire interaction.

2020

Numerical investigation of the mixed-mode failure of snow

Johan Alexandre Philippe Gaume, Dominika Mulak

The failure of a weak snow layer underlying a cohesive slab is the primary step in the release process of a dry snow slab avalanche. The complex and heterogeneous microstructure of snow limits our understanding of failure initiation inside the weak layer, especially under mixed-mode shear–compression loading. Further complication arises from the dependence of snow strength on the loading rate induced by the balance between bond breaking and bond formation (sintering) during the failure process. Here, we use the discrete element method to investigate the influence of mixed-mode loading and fast sintering on the failure of a weak layer generated using cohesive ballistic deposition. Both fast and slow loading simulations resulted in a mixed-mode failure envelope in good agreement with laboratory experiments. We show that the number of broken bonds at failure and the weak layer strength significantly decreases with increasing loading angle, regardless of the loading rate. While the influence of loading rate appears negligible in shear-dominant loading (for loading angles above 30∘), simulations suggest a significant increase in the weak layer strength at low loading angles and low loading rates, characteristic of natural avalanches, due to the presence of an active sintering mechanism.

2019

Microstructure-based modeling of snow using the material point method and finite strain elastoplasticity

Johan Alexandre Philippe Gaume, Henning Löwe, Lars Kristoffer Uhlen Blatny, Stephanie Wang

2020