Item: Measurements of ECT Scores and Crack-Face Friction in Non-Persistent Weak Layers: What are the Implications for Practitioners?
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Title: Measurements of ECT Scores and Crack-Face Friction in Non-Persistent Weak Layers: What are the Implications for Practitioners?
Proceedings: Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
Authors:
- Ron Simenhois [ Coeur Alaska, Juneau, Alaska, USA ]
- Karl W. Birkeland [ USDA Forest Service National Avalanche Center, Bozeman, Montana, USA ]
- Alec van Herwijnen [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
Date: 2012
Abstract: Field observations suggest that avalanches releasing on non-persistent weak layers tend to slide on steeper slopes than other dry slab avalanches. Recent research indicates that the initiation of fracture in a weak snowpack layer is almost unaffected by slope angle. However, this field research included only persistent weak layers. Thus, the question remains: Why are avalanches involving nonpersistent weak layers slope angle sensitive? Our paper investigates the following for non-persistent weak layers: 1) the effect of slope angle on fracture initiation and 2) the friction coefficient. We performed Extended Column Tests (ECTs) on slopes where we could track the number of taps needed for weak layer fracturing on a variety of slope angles (from 8° to 46°) with minimal snow structure change. Our results show that the number of taps required to initiate a fracture that crosses the entire column (ECTP) was mostly independent of slope angle. In addition, we measured the friction coefficient of two different non-persistent weak layers types (PPsd and DFdc) within minutes after avalanches were triggered and in the following days. Our results show that the friction coefficient of non-persistent weak layers was higher than published values for persistent weak layers. From a theoretical perspective, our results are in line with the mixed-mode anticrack model for fracture in a weak snowpack layer. From a practical perspective, our results can contribute to safer pit site selection, terrain and snowpack analysis, and they give us insight into the value of observing downslope block movement after fracturing in stability tests.
Object ID: issw-2012-104-110.pdf
Language of Article: English
Presenter(s): Unknown
Keywords: weak snowpack layers, extended column test, slopes, dry slab avalanche,
Page Number(s): 104-110
Subjects: weak layers Extended Column Test (ECT) non-persistent weak layers
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