Acoustic emission signatures prior to snow failure

Achille Capelli,Ingrid Reiweger,Jürg Schweizer

doi:10.1017/jog.2018.43

Achille Capelli, Ingrid Reiweger + Show 1 more

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https://doi.org/10.1017/jog.2018.43

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Abstract

ABSTRACTSnow slab avalanches are caused by cracks forming and propagating in a weak snow layer below a cohesive slab. The gradual damage process leading to the formation of the initial failure within the weak layer (WL) is still not entirely understood. To this end, we designed a novel test apparatus that allows performing loading experiments with large snow samples (0.25 m2) including a WL at different loading rates and simultaneously monitoring the acoustic emissions (AE) response. By analyzing the AE generated by micro-cracking, we studied the evolution of the damage process preceding snow failure. At fast loading rates, the exponent of the AE energy distribution (b-value) gradually changed, and both the energy rate and the inverse waiting time increased exponentially with increasing load. These changes in AE signature indicate a transition from small to large events and an acceleration of the damage processes leading to brittle failure. For the experiments at slow loading rate, these changes in the AE signature were not or only partially present, even if the sample failed, indicating a different evolution of the damage process. The observed characteristics in AE response provide new insights on how to model snow failure as a critical phenomenon.

Highlights

To model the release of a dry-snow slab avalanche, it is essential to understand how failures in snow initiate and develop
Though we have a good conceptual understanding of the key processes involved in slab avalanche release (e.g. Schweizer and others, 2016), we still lack a detailed understanding of the first stage, the failure initiation process or in other words the gradual damage process leading to the nucleation of the initial failure
We developed a new apparatus that allows performing loadcontrolled snow failure experiments with large snow samples (0.25 m2) at different loading rates and simultaneously monitoring the acoustic emissions (AE) generated during the failure process

Summary

Introduction

To model the release of a dry-snow slab avalanche, it is essential to understand how failures in snow initiate and develop. Though we have a good conceptual understanding of the key processes involved in slab avalanche release (e.g. Schweizer and others, 2016), we still lack a detailed understanding of the first stage, the failure initiation process or in other words the gradual damage process leading to the nucleation of the initial failure. This initial failure can either be caused by an external, rapid, localized load such as a skier or an explosion, or form gradually from local heterogeneities due to slowly changing loading conditions and snow properties. There is still a lack of understanding with regard to their failure behavior, e.g. the failure envelope (Reiweger and others, 2015a), how damage develops into macroscopic cracks and how the loading rate affects the failure behavior

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