Size effect law and fracture mechanics of the triggering of dry snow slab avalanches

Bažant, Zdeněk P.; Zi, Goangseup; McClung, D. M.

doi:10.1029/2002jb001884

Cited by 83 publications

(221 citation statements)

References 24 publications

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“…However, snow slabs of different depths also generally have very different properties at their base, due to densification and sintering. Hence, one should distinguish between the structural size effect which induces a decrease of the strength with the sample size and the material size effect [Bazant et al, 2003]. For snow, existing data suggest a strong increase of the shear strength with the slab depth.…”

Section: Discussionmentioning

confidence: 99%

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Evaluation of slope stability with respect to snowpack spatial variability

Gaume¹,

Schweizer²,

Herwijnen³

et al. 2014

JGR Earth Surface

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The evaluation of avalanche release conditions constitutes a great challenge for risk assessment in mountainous areas. The spatial variability of snowpack properties has an important impact on snow slope stability and thus on avalanche formation, since it strongly influences failure initiation and crack propagation in weak snow layers. Hence, the determination of the link between these spatial variations and slope stability is very important, in particular, for avalanche public forecasting. In this study, a statistical-mechanical model of the slab-weak layer (WL) system relying on stochastic finite element simulations is used to investigate snowpack stability and avalanche release probability for spontaneously releasing avalanches. This model accounts, in particular, for the spatial variations of WL shear strength and stress redistribution by elasticity of the slab. We show how avalanche release probability can be computed from release depth distributions, which allows us to study the influence of WL spatial variations and slab properties on slope stability. The importance of smoothing effects by slab elasticity is verified and the crucial impact of spatial variation characteristics on the so-called knock-down effect on slope stability is revisited using this model. Finally, critical length values are computed from the simulations as a function of the various model parameters and are compared to field data obtained with propagation saw tests.

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Section: Discussionmentioning

confidence: 99%

“…Finally, let us point out that size effects, which are of crucial importance for avalanche release [Bazant et al, 2003], are indirectly addressed in our model. The size effect is defined as the effect of the system size (in our case, the slab depth h) on the fracture toughness or on the strength of the material.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of slope stability with respect to snowpack spatial variability

Gaume¹,

Schweizer²,

Herwijnen³

et al. 2014

JGR Earth Surface

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show abstract

“…Like alpine snow, rock sliding on a joint displays strain softening as do some weak layer soil types on which landslides fail. Realistic prediction of failure may well be concerned with the location and properties of macroscopic imperfections, possibly on the order of magnitude spatial scale of Bažant et al [2003]: L A /D ≈ O(1). It is unlikely that a large rock avalanche initiates from a region of stress concentration and sliding with a scale much less than this.…”

Section: Implications For Snow Avalanche Rock Avalanche and Landslimentioning

confidence: 99%

“…[3] Up until now, all the estimates of the size of sweet spots have been from a theoretical perspective [Bader and Salm, 1990;McClung and Schweizer, 1999;Louchet, 2001;Bažant et al, 2003]. In this paper, the estimates of sweet spot size are estimated from extensive field measurements of critical lengths from shear fracture tests.…”

Section: Introductionmentioning

confidence: 99%

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The critical size of macroscopic imperfections in dry snow slab avalanche initiation

McClung

2011

J. Geophys. Res.

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[1] Dry snow slab avalanches initiate after mode II fracture propagation within a thin, weak layer under a planar slab. Dry alpine snow in which avalanches form is a porous material, typically with volume fraction filled by solids of between 10% and 50%. If snow slab avalanches were caused by small scale flaws, there would be continuous avalanches and alpine snow would not survive on steep slopes. Instead, snow slab avalanches initiate from macroscopic imperfections or weak zones within the weak layer. These are called "sweet spots" by practitioners and deficit zones in the pioneering work by Conway and Abrahamson in the 1980s. In this paper, the results of 750 in situ shear fracture tests from 68 slab-weak layer combinations are summarized in relation to the critical sweet spot length and weak layer crystal form. The results show that the critical sweet spot lengths follow a gamma probability density function with a range from 0.14 to 1.3 m and most probable value 0.5 m. The results also imply that critical sweet spot length depends on weak layer grain type with significantly larger values for persistent forms (surface hoar and facets) than for nonpersistent forms (decomposing and fragmented grains).

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Granulation of snow: From tumbler experiments to discrete element simulations

Steinkogler

Gaume²,

Löwe³

et al. 2015

J. Geophys. Res. Earth Surf.

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It is well known that snow avalanches exhibit granulation phenomena, i.e., the formation of large and apparently stable snow granules during the flow. The size distribution of the granules has an influence on flow behavior which, in turn, affects runout distances and avalanche velocities. The underlying mechanisms of granule formation are notoriously difficult to investigate within large-scale field experiments, due to limitations in the scope for measuring temperatures, velocities, and size distributions. To address this issue we present experiments with a concrete tumbler, which provide an appropriate means to investigate granule formation of snow. In a set of experiments at constant rotation velocity with varying temperatures and water content, we demonstrate that temperature has a major impact on the formation of granules. The experiments showed that granules only formed when the snow temperature exceeded −1 ∘ C. No evolution in the granule size was observed at colder temperatures. Depending on the conditions, different granulation regimes are obtained, which are qualitatively classified according to their persistence and size distribution. The potential of granulation of snow in a tumbler is further demonstrated by showing that generic features of the experiments can be reproduced by cohesive discrete element simulations. The proposed discrete element model mimics the competition between cohesive forces, which promote aggregation, and impact forces, which induce fragmentation, and supports the interpretation of the granule regime classification obtained from the tumbler experiments. Generalizations, implications for flow dynamics, and experimental and model limitations as well as suggestions for future work are discussed.

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Size effect law and fracture mechanics of the triggering of dry snow slab avalanches

Cited by 83 publications

References 24 publications

Evaluation of slope stability with respect to snowpack spatial variability

Evaluation of slope stability with respect to snowpack spatial variability

The critical size of macroscopic imperfections in dry snow slab avalanche initiation

Granulation of snow: From tumbler experiments to discrete element simulations

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