A new mixed‐mode failure criterion for weak snowpack layers

Reiweger, Ingrid; Gaume, Johan; Schweizer, Jürg

doi:10.1002/2014gl062780

Cited by 55 publications

(102 citation statements)

References 26 publications

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“…This failure envelope shows, for realistic values of the slope angle, a much lower strength in shear than in compression as well as a decrease of the shear strength with increasing normal stress. This type of behavior is similar to that reported in recent laboratory (Reiweger et al, 2015) and field (Chandel et al, 2014) experiments on persistent weak snow layers. Hence, the chosen WL structure allows to have different modes of failure (tension, shear, compression and mixed-mode) such as observed in real weak layers and thus has the essential characteristics to model the processes of slab avalanche release.…”

Section: Simulation Protocol and Illustrationsupporting

confidence: 90%

Modeling of crack propagation in weak snowpack layers using the discrete element method

Gaume¹,

Herwijnen²,

Chambon

et al. 2015

The Cryosphere

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Abstract. Dry-snow slab avalanches are generally caused by a sequence of fracture processes including (1) failure initiation in a weak snow layer underlying a cohesive slab, (2) crack propagation within the weak layer and (3) tensile fracture through the slab which leads to its detachment. During the past decades, theoretical and experimental work has gradually led to a better understanding of the fracture process in snow involving the collapse of the structure in the weak layer during fracture. This now allows us to better model failure initiation and the onset of crack propagation, i.e., to estimate the critical length required for crack propagation. On the other hand, our understanding of dynamic crack propagation and fracture arrest propensity is still very limited.To shed more light on this issue, we performed numerical propagation saw test (PST) experiments applying the discrete element (DE) method and compared the numerical results with field measurements based on particle tracking. The goal is to investigate the influence of weak layer failure and the mechanical properties of the slab on crack propagation and fracture arrest propensity. Crack propagation speeds and distances before fracture arrest were derived from the DE simulations for different snowpack configurations and mechanical properties. Then, in order to compare the numerical and experimental results, the slab mechanical properties (Young's modulus and strength) which are not measured in the field were derived from density. The simulations nicely reproduced the process of crack propagation observed in field PSTs. Finally, the mechanical processes at play were analyzed in depth which led to suggestions for minimum column length in field PSTs.

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Section: Simulation Protocol and Illustrationsupporting

confidence: 90%

Modeling of crack propagation in weak snowpack layers using the discrete element method

Gaume¹,

Herwijnen²,

Chambon

et al. 2015

The Cryosphere

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“…This current limitation of our model tends to overestimate the additional stress due to a skier in particular for cases with a hard substratum and a slab whose hardness decreases with increasing depth. In addition, it would be interesting to apply the proposed approach for describing the additional stress induced by a skier within a multi-layered snowpack with more complex models, taking into account the mixed-mode failure behaviour of the weak layer (Reiweger et al, 2015) as well as crack propagation (Reuter et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

Snow instability evaluation: calculating the skier-induced stress in a multi-layered snowpack

Monti¹,

Gaume²,

Herwijnen³

et al. 2016

Nat. Hazards Earth Syst. Sci.

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Abstract. The process of dry-snow slab avalanche formation can be divided into two phases: failure initiation and crack propagation. Several approaches tried to quantify slab avalanche release probability in terms of failure initiation based on shear stress and strength. Though it is known that both the properties of the weak layer and the slab play a major role in avalanche release, most previous approaches only considered slab properties in terms of slab depth, average density and skier penetration. For example, for the skier stability index, the additional stress (e.g. due to a skier) at the depth of the weak layer is calculated by assuming that the snow cover can be considered a semi-infinite, elastic, half-space. We suggest a new approach based on a simplification of the multi-layered elasticity theory in order to easily compute the additional stress due to a skier at the depth of the weak layer, taking into account the layering of the snow slab and the substratum. We first tested the proposed approach on simplified snow profiles, then on manually observed snow profiles including a stability test and, finally, on simulated snow profiles. Our simple approach reproduced the additional stress obtained by finite element simulations for the simplified profiles well -except that the sequence of layering in the slab cannot be replicated. Once implemented into the classical skier stability index and applied to manually observed snow profiles classified into different stability classes, the classification accuracy improved with the new approach. Finally, we implemented the refined skier stability index into the 1-D snow cover model SNOWPACK. The two study cases presented in this paper showed promising results even though further verification is still needed. In the future, we intend to implement the proposed approach for describing skier-induced stress within a multi-layered snowpack into more complex models which take into account not only failure initiation but also crack propagation.

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“…Failure criterion FC 1 of our modeled weak layer (black circles) obtained from mixed-mode shear-compression loading tests. FC 2 is the high-rate mixed-mode failure envelope found by Reiweger et al (2015). The grey dotted lines represent angles of loading ψ such as tan ψ = τ g /σ n where τ g is the shear stress.…”

Section: Discrete Element Modelmentioning

confidence: 99%

“…3). Through the triangular shape of the WL structure, the main features of real WL failure envelopes (Chandel et al, 2014;Reiweger et al, 2015) Figure 2. Successive snapshots (a-e) of a DEM simulation of the propagation saw test (PST).…”

Section: Discrete Element Modelmentioning

confidence: 99%

Snow fracture in relation to slab avalanche release: critical state for the onset of crack propagation

Gaume

Herwijnen²,

Chambon

et al. 2017

The Cryosphere

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Abstract. The failure of a weak snow layer buried below cohesive slab layers is a necessary, but insufficient, condition for the release of a dry-snow slab avalanche. The size of the crack in the weak layer must also exceed a critical length to propagate across a slope. In contrast to pioneering shear-based approaches, recent developments account for weak layer collapse and allow for better explaining typical observations of remote triggering from low-angle terrain. However, these new models predict a critical length for crack propagation that is almost independent of slope angle, a rather surprising and counterintuitive result. Based on discrete element simulations we propose a new analytical expression for the critical crack length. This new model reconciles past approaches by considering for the first time the complex interplay between slab elasticity and the mechanical behavior of the weak layer including its structural collapse. The crack begins to propagate when the stress induced by slab loading and deformation at the crack tip exceeds the limit given by the failure envelope of the weak layer. The model can reproduce crack propagation on low-angle terrain and the decrease in critical length with increasing slope angle as modeled in numerical experiments. The good agreement of our new model with extensive field data and the ease of implementation in the snow cover model SNOWPACK opens a promising prospect for improving avalanche forecasting.

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A new mixed‐mode failure criterion for weak snowpack layers

Cited by 55 publications

References 26 publications

Modeling of crack propagation in weak snowpack layers using the discrete element method

Modeling of crack propagation in weak snowpack layers using the discrete element method

Snow instability evaluation: calculating the skier-induced stress in a multi-layered snowpack

Snow fracture in relation to slab avalanche release: critical state for the onset of crack propagation

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