Stress measurements in the snow cover below localized dynamic loads

Thumlert, Scott; Jamieson, Bruce

doi:10.1016/j.coldregions.2014.06.002

Cited by 22 publications

(17 citation statements)

References 14 publications

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“…The fitted models from Fig. 5 are in the expected range compared to previous experimental results (Schweizer and Camponovo, 2001;Thumlert and Jamieson, 2014;Thumlert et al, 2013). The data showed that harder snow covers increased the difference between the stress profiles from skiing and isolated column tests (Figs.…”

Section: Column Isolationsupporting

confidence: 56%

Stress measurements from common snow slope stability tests

Thumlert

Jamieson

2015

Cold Regions Science and Technology

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In the majority of fatal snow avalanches, skiers and snowmobilers trigger the avalanche by applying load to the snow cover. The snow cover is often tested to learn information about its stability on surrounding slopes. This testing is normally performed by digging down into the snow cover, isolating a column of snow, dynamically loading the top of the column and observing fractures that occur in the column due to the loading. Understanding how stress from dynamic surface loads and from loading in common stability tests transmit through the snow cover can help people avoid situations in which they can trigger avalanches. Capacitive sensors were used within the mountain snow cover to measure peak stress below dynamic surface loads and in common stability tests. The sensors were used on 21 field days to collect over 1,605 measurements. We present measured stress data illustrating the effect of isolating a column in stability tests compared to skiing and snowmobiling over a largely undisturbed snow cover. We observed that adjusting the depth of stability tests to account for the penetration depth of snowmobiles loads the snow cover more similarly to the loading applied by snowmobiling. We found that the stress profile in stability tests more closely matched skiing and snowmobiling when the snow cover was softer compared to when the snow cover was harder. Similarly, the differences between the skier and snowmobile loading compared to the stability test loading were increased for a harder snow cover. Finally, in the Extended Column Test, a modern stability test, stress was only measured directly below the loading and not on the opposite side of the column.

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Section: Column Isolationsupporting

confidence: 56%

Stress measurements from common snow slope stability tests

Thumlert

Jamieson

2015

Cold Regions Science and Technology

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“…In the avalanche domain, this effect is often called "bridging". Thumlert and Jamieson (2014) recently coupled the "bridging index" introduced by Schweizer and Jamieson (2003) to the classical skier stability index. This "bridging index" corresponds to the sum of the hardness of the different slab layers, weighted by the respective depth.…”

Section: Additional Skier Stress Within a Multi-layered Snowpackmentioning

confidence: 99%

“…In particular, slab hardness influences the stress distribution below a skier, e.g. low values are found below hard slabs (Schweizer et al, 1995;Camponovo and Schweizer, 1997;Schweizer and Camponovo, 2001;Thumlert and Jamieson, 2014). Furthermore, the hardness of the substratum may also play a significant role, hard layers (such as crusts) just below the weak layer act as stress concentrators in the weak layer (van Herwijnen and Jamieson, 2007;Habermann et al, 2008).…”

Section: Introductionmentioning

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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“…1b). The initial failure resulting in a macroscopic crack in the WL develops from microscale heterogeneities by damage accumulation (Schweizer et al, 2008;Gaume et al, 2014b) or directly below a local overload such as a skier or a snowmobile (van Herwijnen and Jamieson, 2005;Thumlert and Jamieson, 2014). Stress concentrations at the crack tips will then determine whether crack propagation and eventually slope failure occurs (McClung, 1979;Schweizer et al, 2003), even when the average overlying stress is lower than the average weak layer strength (knock-down effect; Fyffe and Zaiser, 2004;Gaume et al, 2012Gaume et al, , 2013Gaume et al, , 2014b.…”

Section: Introductionmentioning

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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Stress measurements in the snow cover below localized dynamic loads

Cited by 22 publications

References 14 publications

Stress measurements from common snow slope stability tests

Stress measurements from common snow slope stability tests

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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