On the mechanics of snow slab release

Bader, Henri; Salm, B.

doi:10.1016/s0165-232x(05)80007-2

Cited by 58 publications

(48 citation statements)

References 5 publications

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“…Virtually all modern work on thc snow slab (McClung, 1979(McClung, ,1981(McClung, ,1987Conway and Abrahamson, 1988;Bader and Salm, 1990;Conway, 1998) postulates that the size effects controlling avalanche release are macroscopic, with a size effcct independent of statistical properties in agreement with the arguments of Bazant and Planas. The sizc effects associated with sample-size dependence as in the (brittle) shcar frame test are microscopic and dependent on statistical properties.~ficroscopic flaws are present in abundance everywhere in alpine snow and there is evidence that such flaws are important for interpreting shear frame results.…”

Section: Simple Analysis With Imperfection In a Weak Layermentioning

confidence: 83%

Skier triggering, snow temperatures and the stability index for dry-slab avalanche initiation

McClung

Schweizer²

1999

J. Glaciol.

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ABSTRACT. For more than 30 years the quantitative method of evaluating stability (e.g. Roch, 1966; Fohn, 1987;Jamieson, 1995;Jamieson andJohnston, 1998a) has been focused on calculation ora strength-to-load ratio (or stability index): when the shear stress applied to the weak layer reaches the shcar strength, failure is imminent. Howcver, field observations combined with experience and measurements indicate that snow-slab temperatures and slab hardness can have a strong inLluenceon dry-snow slab stability. In this paper, we present a simple static analysis of the stability index, and discuss the importance of slab temperatures and hardness and macroscopic size effects (factors not contained in the stability index) on snow-slab stability. Our conclusion is that the traditional mcthod lacks some elements which arc very important in snow-slab stability, particularly when skier triggering is involved.

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Section: Simple Analysis With Imperfection In a Weak Layermentioning

confidence: 83%

Skier triggering, snow temperatures and the stability index for dry-slab avalanche initiation

McClung

Schweizer²

1999

J. Glaciol.

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“…It is generally accepted that dry snow slab avalanche release originates from shear failure in a thin weak layer (Schweizer 1998). Most models of slab avalanche release (McClung 1981;Bader and Salm 1990) are based on linear fracture mechanics. They assume the existence of initial shear-failure planes or "deficit" areas (super weak zone) as a necessary condition for the start of fracture propagation.…”

Section: Discussionmentioning

confidence: 99%

Strain localization in a continuum as an instability event

Chiaia

Ferro

2006

Int J Fract

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The paper presents a novel physical model, based on perturbation theory, to describe localization pattern formation in a solid material as a result of system instabilities. Such kind of approach has been inspired by the theory of population dynamics. In particular, the sinergetic phenomenon of strain localization into a stressed continuum, and its subsequent evolution to cohesive cracking, is obtained through the competition of an external source of energy (e.g., strain energy) and of the internal behavior of the material. The hypothesis of mobile energy entities within material bulk is put forward. These entities, which under low strain conditions are evenly distributed throughout the body, can be considered as strain quanta. The quantization of mechanical quantities is not new in continuum and fracture mechanics, [see, e.g., Novozhilov (1969, Prik Mat Mek 33:212-222)]. With increasing strain, a certain critical point is reached when the homogeneous situation becomes unstable and the strain quanta begin to aggregate into bands, leading to periodic strain localization patterns. The model, which is only theoretical at this stage, can be applied to the particular case of dry snow avalanches. In these cases, snow avalanche triggering is due to instability (onset of sliding onto a weak plane) and is controlled by external loading (e.g., weight of the slope, load by skiers) and by internal factors (e.g., temperature changes, snow phase transformations etc.).

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“…Bažant et al [2003] predicted that L A /D ≈ O(1) which is also consistent with the median predictions in this paper. Bader and Salm [1990] predicted critical lengths of 10 m and Louchet [2001] predicted critical lengths ranging from about 10 m to 80 m. These latter two estimates are so large that field testing during skiing and in situ instability test observations easily eliminate them.…”

Section: Comparison With Previous Estimatesmentioning

confidence: 95%

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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On the mechanics of snow slab release

Cited by 58 publications

References 5 publications

Skier triggering, snow temperatures and the stability index for dry-slab avalanche initiation

Skier triggering, snow temperatures and the stability index for dry-slab avalanche initiation

Strain localization in a continuum as an instability event

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

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