Dry-snow slab avalanches initiate from a failure in a weak snow layer below a cohesiveslab. Snow is considered as a porous ice structure, and the strength distribution of the single elements ofthis structure, i.e. grains and bonds between grains, shows a high degree of disorder. On the bond ormicrostructural level, the failure process is believed to start if the fracturing of bonds between snowgrains is not balanced by the formation of new bonds. We use a statistical fracture model – a fibrebundle model – to study the failure process in a weak snow layer. The model consists of fibres of variousstrengths representing single snow grains between two rigid plates which represent the slab above andthe substratum below the weak layer. The fibres deform in a linear elastic manner and break instantly attheir rupture strength. Broken fibres may sinter (re-bond) and regain strength after a finite sinteringtime. We show that the different characteristic times for breaking and sintering lead to the ratedependence of snow strength. This is, to our knowledge, the first statistical model to reproduce theductile-to-brittle transition which snow exhibits with increasing strain rate. When the model is appliedto simulate experimental stress–strain curves for different strain rates, the model and experimentalresults are in fair agreement.
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