Measurements of weak layer fracture energy

Schweizer, Jürg; Herwijnen, Alec van; Reuter, Benjamin

doi:10.1016/j.coldregions.2011.06.004

Cited by 46 publications

(43 citation statements)

References 19 publications

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“…Köchle and Schneebeli (2014) also mentioned the limited resolution of a traditional snow profile as a major drawback for the characterization of weak layers. Density variations are also known to have a large influence on mechanical properties (Schweizer et al, 2011) and on microwave signatures as they act as interfaces for wave reflection (Wiesmann and Mätzler, 1999).…”

Section: Unresolved Variationmentioning

confidence: 99%

“…The biological and photochemical activities of snow are related to snow density (Domine et al, 2008). Further, snow mechanical parameters are linked to density (Schneebeli and Johnson, 1998;Wang and Baker, 2013) and snowpack stability depends on vertical density variations (Schweizer et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

“…In addition, parametrization of snow physical properties such as permeability (Shimizu, 1970;Calonne et al, 2012;Zermatten et al, 2014) and thermal conductivity (Adams and Sato, 1993;Sturm et al, 1997;Calonne et al, 2011) are linked to density. Snow models like SNTHERM (Jordan, 1991), CROCUS (Brun et al, 1989), and SNOWPACK (Lehning et al, 2002) adopted density for the parametrizations of such properties, and models describing ventilation and air flow (Albert, 1996), isotopic content in polar snow (Neumann and Waddington, 2004;Town et al, 2008), or drifting snow (Lenaerts et al, 2012) also require density.…”

Section: Introductionmentioning

confidence: 99%

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Intercomparison of snow density measurements: bias, precision, and vertical resolution

Proksch

Rutter

Fierz³

et al. 2016

The Cryosphere

104

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Abstract. Density is a fundamental property of porous media such as snow. A wide range of snow properties and physical processes are linked to density, but few studies have addressed the uncertainty in snow density measurements. No study has yet quantitatively considered the recent advances in snow measurement methods such as micro-computed tomography (µCT) in alpine snow. During the MicroSnow Davos 2014 workshop, different approaches to measure snow density were applied in a controlled laboratory environment and in the field. Overall, the agreement between µCT and gravimetric methods (density cutters) was 5 to 9 %, with a bias of −5 to 2 %, expressed as percentage of the mean µCT density. In the field, density cutters overestimate (1 to 6 %) densities below and underestimate (1 to 6 %) densities above a threshold between 296 to 350 kg m −3 , dependent on cutter type. Using the mean density per layer of all measurement methods applied in the field (µCT, box, wedge, and cylinder cutters) and ignoring ice layers, the variation between the methods was 2 to 5 % with a bias of −1 to 1 %. In general, our result suggests that snow densities measured by different methods agree within 9 %. However, the density profiles resolved by the measurement methods differed considerably. In particular, the millimeter-scale density variations revealed by the high-resolution µCT contrasted the thick layers with sharp boundaries introduced by the observer. In this respect, the unresolved variation, i.e., the density variation within a layer which is lost by lower resolution sampling or layer aggregation, is critical when snow density measurements are used in numerical simulations.

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Section: Unresolved Variationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Intercomparison of snow density measurements: bias, precision, and vertical resolution

Proksch

Rutter

Fierz³

et al. 2016

The Cryosphere

104

View full text Add to dashboard Cite

show abstract

“…In general, only the slab depth and its average density were considered within the above-mentioned approaches for quantifying the amount of stress reaching the weak layer (Föhn, 1987b). However, the multi-layer character of the snowpack, generally not taken into account, plays a significant role not only in the failure initiation process (Habermann et al, 2008) but also in crack propagation (Heierli and Zaiser, 2007;Sigrist and Schweizer, 2007;van Herwijnen and Jamieson, 2007;Schweizer et al, 2011). Indeed, the layered character of the snow cover determines the amount of stress at the depth of the weak layer (Schweizer, 1993;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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“…Presently, it can be estimated using three existing methods: (i) through PTV or finite element analysis of the PST (Sigrist and Schweizer, 2007;van Herwijnen et al, 2010Schweizer et al, 2011), (ii) from snow micro-penetrometer (SMP) measurements (Schneebeli et al, 1999) by integrating the penetration resistance over the thickness of the WL (Reuter et al, 2015), and (iii) from X-ray computer tomography-based (CT) microstructural models (LeBaron and Miller, 2014). Depending on the method, estimates of the WL specific fracture energy can differ by as much as 2 orders of magnitude, resulting in widely different values of the critical crack length.…”

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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Measurements of weak layer fracture energy

Cited by 46 publications

References 19 publications

Intercomparison of snow density measurements: bias, precision, and vertical resolution

Intercomparison of snow density measurements: bias, precision, and vertical resolution

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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