Item: Measuring snow mechanical properties typical of storm snow instabilities
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Title: Measuring snow mechanical properties typical of storm snow instabilities
Proceedings: International Snow Science Workshop Proceedings 2018, Innsbruck, Austria
Authors:
- Benjamin Reuter [ Montana State University, Department of Civil Engineering, 205 Cobleigh Hall, Bozeman, MT 59717, U.S.A. ] [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Neige Calonne [ Montana State University, Department of Civil Engineering, 205 Cobleigh Hall, Bozeman, MT 59717, U.S.A. ] [ Météo-France - CNRS, CNRM-GAME, URA1357, CEN, Grenoble, France ]
- Ed Adams [ Montana State University, Department of Civil Engineering, 205 Cobleigh Hall, Bozeman, MT 59717, U.S.A. ]
Date: 2018-10-07
Abstract: Dry snow slab avalanches release after failure has occurred in a weak layer below a cohesive snow slab. Typically, weak layers either consist of precipitation particles or persistent grain types. In view of forecasting, active times of such weak layers are significantly shorter for precipitation particles. Hence, studying the characteristics of storm snow instabilities in the field requires good timing and are challenging since the peak of these instabilities occurs most likely during or toward the end of a storm - when weather conditions hinder traditional field measurements. To overcome these difficulties, we investigated storm snow instabilities based on cold-laboratory experiments. Demonstrated techniques allow layers of nature representative snow to be artificially created in the laboratory. We created different artificial snowpack made of a base layer, a weak layer, and a slab layer by either growing crystals or depositing sifted disaggregated particles. Weak layers of decomposing fragmented particles were created to mimic storm snow snowpack; persistent weak layers of surface hoar and facets were also created to allow comparisons. After some defined time lag we loaded snow samples in a mechanical testing apparatus in shear to measure displacement, strain and failure using an image correlation technique. Micro computed snow tomography and snow micropenetrometry captured the microstructural properties at and around the interface where failure occurred. Our results show that the shear strain was concentrated in the weak layer. Failure occurred after plastic deformation. Measured values of shear strength and shear modulus were similar for the different the weak layers, and tended to increase after burial. This observation is most likely due to the growth of grain bonds occurring during isothermal metamorphism.
Object ID: ISSW2018_O10.3.pdf
Language of Article: English
Presenter(s):
Keywords: snow failure, snow mechanics, mechanical properties, snow instability, storm snow
Page Number(s): 866-870
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