Item: On How the Tensile Strength of the Slab Affects Crack Propagation Propensity
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Title: On How the Tensile Strength of the Slab Affects Crack Propagation Propensity
Proceedings: International Snow Science Workshop 2014 Proceedings, Banff, Canada
Authors:
- Jürg Schweizer [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Benjamin Reuter [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Alec van Herwijnen [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Dave Gauthier [ Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON, Canada ]
- Bruce Jamieson [ Department of Civil Engineering, University of Calgary, Calgary, AB, Canada ]
Date: 2014-09-29
Abstract: The release of a dry-snow slab avalanche is preceded by a series of fractures. The two key processes involved are (1) failure initiation within the weak layer underlying the slab, probably due to damage accumulation by enhanced deformation, and (2) crack propagation, once the initial failure has reached a critical size – leading to the detachment of the slab. The focus on crack propagation has clearly improved our understanding of avalanche formation. The propagation saw test (PST) is the only in-situ fracture mechanical test and allows testing the crack propagation propensity. When conducting such tests, we observe that cracks sometimes only propagate a short distance, not to the end of the column, and stop at a crack through the slab. Furthermore, even if the crack propagates to the end of the column, conditions for slope failure, in other words slab avalanche release, are not always present on adjacent slopes. We calculate the tensile stress with a simple cantilever beam model and with finite element simulations. Results are compared to numerous PSTs from Canada to explore the relevance of slab properties, in particular the tensile strength, for crack propagation. Model results suggest that the slab needs a certain density in order to have sufficient strength and not fail in tension during the initial states of crack propagation. Analyzing the field data showed that the characteristics of the slab were significantly different in those PSTs where slab fractures (SF) were observed from those where the crack propagated to the end of the column (END) or arrested without slab fracture (ARR). The test result SF was associated with thin, soft and low density slabs. Whereas soft slabs provide ample deformation energy, they are prone to slab fractures. On the other hand, stiff slabs may require large crack lengths, until propagation starts – if at all, but due to their high tensile strength, propagation may be extensive. Obviously, there is an optimal range of slab stiffness allowing crack onset as well as crack propagation – the tensile strength of the slab might well be the limiting factor.
Object ID: ISSW14_paper_O7.02.pdf
Language of Article: English
Presenter(s):
Keywords: avalanche release, snow stability evaluation, avalanche forecasting, fracture
Page Number(s): 179-184
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