Measurement of fracture mechanical properties of snow and application to dry snow slab avalanche release

Sigrist, Christian

doi:10.3929/ethz-a-005282374

Cited by 7 publications

(4 citation statements)

References 15 publications

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“…The snow properties were selected to represent a meta-stable slab and weak-layer system where the natural release is not possible but only the skier-triggering. Different snow mechanical properties can be related to each other (Jamieson and Johnston, 1990;Scapozza and others, 2004;Sigrist, 2006). In general, it has been demonstrated that the increase in slab depth will also increase the snow density, elastic modulus, and shear strength of the weak layer.…”

Section: Skier-triggering Probabilitymentioning

confidence: 97%

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Influence of slab depth spatial variability on skier-triggering probability and avalanche size

Meloche,

Guillet,

Gauthier

et al. 2024

Ann. Glaciol.

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Spatial variability of snowpack properties adds uncertainty in the evaluation of avalanche hazard. We propose a combined mechanical–statistical approach to study how spatial variation of slab depth affects the skier-triggering probability and possible release size. First, we generate multiple slab depth maps on a plane fictional slope based on Gaussian Random Fields (GRF) for a specific set of mean, variance and correlation length. For each GRF, we derive analytically the Skier Propagation Index (SPI). We then simulate multiple skier tracks and computed the probability based on the number of skier hits where SPI is below 1. Finally, we use a depth-averaged material point method to evaluate the possible avalanche size for given slab depth variations. The results of this analysis show that large correlation lengths and small variances lead to a lower probability of skier-triggering as it reduces the size and the number of areas with low slab depth. Then, we show the effect of skiing style and skier group size on skier-triggering probability. Spatial variability also affects the possible avalanche size by adding stress fluctuation causing early or late tensile failure. Finally, we demonstrate with our models the well-known relationship between the probability and the size in avalanche forecasting.

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Section: Skier-triggering Probabilitymentioning

confidence: 97%

“…The slope angle is also the same as the previous method set at 35 • . We used the empirical power-law fit to link the slab tensile strength with the mean slab density according to Sigrist (2006):…”

mentioning

confidence: 99%

Influence of slab depth spatial variability on skier-triggering probability and avalanche size

Meloche,

Guillet,

Gauthier

et al. 2024

Ann. Glaciol.

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“…For applications, the elastic moduli must be related to accessible parameters of snow. The most common way are empirical parameterizations based on density, or equivalently, ice volume fraction φ. Density based parameterization often state a power law (Frolov and Fedyukin, 1998;Sigrist, 2006;Gerling et al, 2017) or exponential relationships (Köchle and Schneebeli, 2014;Scapozza, 2004) to comply with the observed drastic increase of elasticity of snow with increasing density. The different density based parametrizations for low density snow have been compared in many publications (e.g.…”

Section: Snow: Power Law Modelsmentioning

confidence: 99%

A microstructure-based parameterization of the effective, anisotropic elasticity tensor of snow, firn, and bubbly ice

Sundu¹,

Freitag

Fourteau

et al. 2023

Preprint

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Abstract. Quantifying the link between microstructure and effective elastic properties of snow, firn, and bubbly ice is essential for many applications in cryospheric sciences. The microstructure of snow and ice can be characterized by different types of fabrics (crystallographic, geometrical) that gives rise to macroscopically anisotropic elastic behavior. While the impact of the crystallographic fabric has been extensively studied in deep firn, the present work investigates the influence of the geometrical fabric over the entire range of possible volume fractions. To this end we have computed the effective elasticity tensor of snow, firn, and ice by finite element simulations based on 395 X-ray tomography images comprising samples from the laboratory, Alps, Greenland, and Antarctica. We employed a variant of the Eshelby tensor that has been previously utilized for the parametrization of thermal and dielectric properties of snow and utilized Hashin-Shtrikman bounds to capture the nonlinear interplay between density and geometrical anisotropy. From that we derive a closed-form parametrization for all components of the (transverse isotropic) elastic tensor for all volume fractions using 2 fit parameters per tensor component. Finally we used the Thomsen parameter to compare the geometrical anisotropy to the crystallographic anisotropy in bubbly ice. While the geometrical anisotropy is clearly dominating up to ice volume fractions of Ø ≈ 0.7, a thorough understanding of elasticity in bubbly ice may require a coupled elastic theory that includes geometrical and crystallographic anisotropy.

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“…Weak-layer stresses are evaluated in its vertical center. by Sigrist (2006), where ρ 0 = 917 kg m −3 is the density of ice. This illustrates the potential of tensile slab fracture.…”

Section: Finite-element Reference Modelmentioning

confidence: 99%

A closed-form model for layered snow slabs

Weißgraeber¹,

Rosendahl²

2023

The Cryosphere

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Abstract. We propose a closed-form analytical model for the mechanical behavior of stratified snow covers for the purpose of investigating and predicting the physical processes that lead to the formation of dry-snow slab avalanches. We represent the system of a stratified snow slab covering a collapsible weak layer by a beam composed of an arbitrary number of layers supported by an anisotropic elastic foundation in a two-dimensional plane-strain model. The model makes use of laminate mechanics and provides slab deformations, stresses in the weak layer, and energy release rates of weak-layer anticracks in real time. The quantities can be used in failure models of avalanche release. The closed-form solution accounts for the layering-induced coupling of bending and extension in the slab and of shear and normal stresses in the weak layer. It is validated against experimentally recorded displacement fields and a comprehensive finite-element model indicating very good agreement. We show that layered slabs cannot be homogenized into equivalent isotropic bodies and reveal the impact of layering on bridging with respect to weak-layer stresses and energy release rates. It is demonstrated that inclined propagation saw tests allow for the determination of mixed-mode weak-layer fracture toughnesses. Our results suggest that such tests are dominated by mode I when cut upslope and comprise significant mode II contributions when cut downslope. A Python implementation of the presented model is publicly available as part of the Weak Layer Anticrack Nucleation Model (WEAC) software package under https://github.com/2phi/weac (last access: 28 March 2023) and https://pypi.org/project/weac (last access: 28 March 2023, Rosendahl and Weißgraeber, 2022).

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Measurement of fracture mechanical properties of snow and application to dry snow slab avalanche release

Cited by 7 publications

References 15 publications

Influence of slab depth spatial variability on skier-triggering probability and avalanche size

Influence of slab depth spatial variability on skier-triggering probability and avalanche size

A microstructure-based parameterization of the effective, anisotropic elasticity tensor of snow, firn, and bubbly ice

A closed-form model for layered snow slabs

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