Evaluation of a prototype field test for fracture and failure propagation propensity in weak snowpack layers

Gauthier, David A.; Jamieson, Bruce

doi:10.1016/j.coldregions.2007.04.005

Cited by 68 publications

(124 citation statements)

References 13 publications

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“…While substantial progress has been made, application with regard to avalanche forecasting or hazard mapping is still hindered in part by our lack of understanding of the dynamic phase of crack propagation. For instance, based on practitioners' experience, it is not uncommon to perform PST field measurements with widespread crack propagation in 1 day, while a few days later, with seemingly very few changes in snowpack properties, cracks will no longer propagate (Gauthier and Jamieson, 2008). Thus far, there is no clear theoretical framework to interpret such observations, and it is not clear how and which snowpack properties affect dynamic crack propagation.…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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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“…Sigrist and Schweizer (2007) were the first to estimate w f with field experiments and finite element (FE) modeling. Their method requires a Propagation Saw Test (PST;van Herwijnen and Jamieson, 2005;Sigrist and Schweizer, 2007;Gauthier and Jamieson, 2008) to determine the critical cut length r c and a snow micro-penetrometer measurement (SMP; Schneebeli and Johnson, 1998) to estimate the effective elastic modulus E of the slab. While Sigrist and Schweizer (2007) reported a mean fracture energy of 0.07 J m −2 , more recent results using the same methodology on eight different weak layers indicate substantially larger values, typically around 1 J m -2 (Schweizer and others, 2011).…”

Section: Introductionmentioning

confidence: 99%

Estimating the effective elastic modulus and specific fracture energy of snowpack layers from field experiments

Herwijnen¹,

Gaume²,

Bair

et al. 2016

J. Glaciol.

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ABSTRACT. Measurements of the mechanical properties of snow are essential for improving our understanding and the prediction of snow failure and hence avalanche release. We performed fracture mechanical experiments in which a crack was initiated by a saw in a weak snow layer underlying cohesive snow slab layers. Using particle tracking velocimetry (PTV), the displacement field of the slab was determined and used to derive the mechanical energy of the system as a function of crack length. By fitting the estimates of mechanical energy to an analytical expression, we determined the slab effective elastic modulus and weak layer specific fracture energy for 80 different snowpack combinations, including persistent and nonpersistent weak snow layers. The effective elastic modulus of the slab ranged from 0.08 to 34 MPa and increased with mean slab density following a power-law relationship. The weak layer specific fracture energy ranged from 0.08 to 2.7 J m −2 and increased with overburden. While the values obtained for the effective elastic modulus of the slab agree with previously published low-frequency laboratory measurements over the entire density range, the values of the weak layer specific fracture energy are in some cases unrealistically high as they exceeded those of ice. We attribute this discrepancy to the fact that our linear elastic approach does not account for energy dissipation due to non-linear parts of the deformation in the slab and/or weak layer, which would undoubtedly decrease the amount of strain energy available for crack propagation.

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“…Hazen plotting positions were used to represent the nonexceedance probability as P = (i − 0.5)/68 where i is the rank of a datum. Data sources for the 750 tests include Gauthier [2007], Sigrist [2006], Gauthier and Jamieson [2008], and data from our group at the University of British Columbia [McClung, 2009a]. Approximately 90% of the measurements come from Gauthier [2007] and Gauthier and Jamieson [2008].…”

Section: Estimate Of Sweet Spot Lengthsmentioning

confidence: 99%

“…Data sources for the 750 tests include Gauthier [2007], Sigrist [2006], Gauthier and Jamieson [2008], and data from our group at the University of British Columbia [McClung, 2009a]. Approximately 90% of the measurements come from Gauthier [2007] and Gauthier and Jamieson [2008]. For the 68 combinations, the mean and median lengths are: 0.64 m and 0.60 m. The most probable length from the mode of the gamma distribution is 0.53 m. The range is: 0.14 m to 1.3 m.…”

Section: Estimate Of Sweet Spot Lengthsmentioning

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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Evaluation of a prototype field test for fracture and failure propagation propensity in weak snowpack layers

Cited by 68 publications

References 13 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

Estimating the effective elastic modulus and specific fracture energy of snowpack layers from field experiments

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

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