Abstract
Abstract. Snowpack weak layers may fail due to excess stresses of various natures, caused by snowfall, skiers, explosions or strong ground motion due to earthquakes, and lead to snow avalanches. This research presents a numerical model describing the failure of "sandwich" snow samples subjected to shaking. The finite element model treats weak layers as interfaces with variable mechanical parameters. This approach is validated by reproducing cyclic loading snow fracture experiments. The model evaluation revealed that the Mohr–Coulomb failure criterion, governed by cohesion and friction angle, was adequate to describe the experiments. The model showed the complex, non-homogeneous stress evolution within the snow samples and especially the importance of tension on fracture initiation at the edges of the weak layer, caused by dynamic stresses due to shaking. Accordingly, a simplified analytical solution, ignoring the inhomogeneity of tangential and normal stresses along the failure plane, may incorrectly estimate the shear strength of the weak layers. The values for "best fit" cohesion and friction angle were ≈1.6 kPa and 22.5–60°. These may constitute valuable first approximations in mechanical models used for avalanche forecasting.
Highlights
Dry snow avalanche release mechanics present a key research question
Various mechanical models that have been used to address the dry snow slab avalanche release problem focused on weak layer failure: e.g. crack models inspired by the over-consolidated clay theory (McClung, 1979), cellularautomata models (Fyffe and Zaiser, 2004), fibre-bundle model (Reiweger et al, 2009), physical-statistical models (Chiaia and Frigo, 2009), multiple finite element method, FEM (Stoffel, 2005; Podolskiy et al, 2013), and analytical and empirical models (Zeidler and Jamieson, 2006)
As cohesion c and friction angle φ that minimise the time dif- the block changes its direction of movement and experiference between instants of failure predicted by the model ences high accelerations, we observe the expected emergence and those measured in the experiments
Summary
Various mechanical models that have been used to address the dry snow slab avalanche release problem focused on weak layer failure: e.g. crack models inspired by the over-consolidated clay theory (McClung, 1979), cellularautomata models (Fyffe and Zaiser, 2004), fibre-bundle model (Reiweger et al, 2009), physical-statistical models (Chiaia and Frigo, 2009), multiple finite element method, FEM (Stoffel, 2005; Podolskiy et al, 2013), and analytical and empirical models (Zeidler and Jamieson, 2006). Recent studies, based on FEM with interfacial constitutive laws for weak layers, have shown that one of the key uncertainties in avalanche forecasting, spatial heterogeneity of weak layers, can be treated by statistical methods and that its importance is reduced for greater snow slab depths (Gaume, 2012; Gaume et al, 2012, 2013). Previous studies were mainly designed to investigate: (1) the stress state of a snow slab on a slope (Smith et al, 1972; Curtis and Smith, 1974; Smith and Curtis, 1975; McClung, 1979), (2) snow deformation (Lang and Sommerfeld, 1977), (3) skier loading (Schweizer, 1993; Wilson et al, 1999; Jones et al, 2006; Habermann et al, 2008; Mahajan et al, 2010), (4) weak layer heterogeneity, super weak zone length and stress concentration, as well as avalanche release slope
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