Numerical investigation of the mixed-mode failure of snow

Dominika Mulak,Johan Gaume

doi:10.1007/s40571-019-00224-5

Dominika Mulak, Johan Gaume

Open Access

https://doi.org/10.1007/s40571-019-00224-5

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Abstract

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^{circ }), 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.

Highlights

The origin of avalanche release can be traced back to a microscale crack which develops in a weak snow layer (Fig. 1) of significantly lower mechanical strength in comparison with the strongly bonded snow slab it is buried beneath [30,32,33]
discrete element method (DEM) loading simulations of a weak layer formed by cohesive ballistic deposition and buried under a cohesive slab layer resulted in a modified mixed-mode failure envelope with failure modes in tension, shear and compression
Simulated failure envelopes obtained with or without sintering were in good agreement with data from laboratory experiments of snow failure performed for fast or slow loading, respectively, and with the Mohr–Coulomb-Cap (MCC) model proposed by Reiweger et al [25]

Summary

Introduction

The origin of avalanche release can be traced back to a microscale crack which develops in a weak snow layer (Fig. 1) of significantly lower mechanical strength in comparison with the strongly bonded snow slab it is buried beneath [30,32,33]. Knowledge of the failure criterion of snow is crucial to avalanche hazard assessment, quantifying the maximum magnitude of stress a weak layer can withstand depending on the slab load and the slope angle. Several previous studies suggested a pure shear [19] or Mohr–Coulomb (MC) criterion for weak snow layer failure [6,8,9,10,14,23,24]. Under this model, failure is predicted to occur only for slope angles larger than the angle of internal friction, typically above 20◦. Despite a better understanding of snow mixed-mode failure, its micromechanical features (localized or diffuse failure [22]) are still not fully understood

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Discussion

Conclusion