Item: Edge Effects In Propagation Tests
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Title: Edge Effects In Propagation Tests
Proceedings: International Snow Science Workshop Grenoble – Chamonix Mont-Blanc - October 07-11, 2013
Authors:
- Edward H. Bair [ US Army Corps of Engineers Cold Regions Research and Engineering Laboratory, Hanover, NH, USA ] [ Earth Research Institute, University of California, Santa Barbara, CA, USA ]
- Ron Simenhois [ Southeast Alaska Avalanche Center, Juneau, AK, USA ]
- Alec van Herwijnen [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Karl Birkeland [ US Forest Service National Avalanche Center, Bozeman, MT, USA ]
Date: 2013-10-07
Abstract: Guidelines suggest beams with lengths around 1 m for Extended Column Tests (ECTs) and Propagation Saw Tests (PSTs). The longest unstable tests published thus far have been about 3m. We define unstable tests as “ECTP/ECTPV†or “PST End†with a cut length ≤ 50 cm. To examine edge effects and other biases, we performed 157 ECTs and PSTs with beams lengths 1-10 m. On days with unstable 1 m tests, we then made hi-speed or hi-definition video recordings of tests on beams 2-10 m long, including 33 tests on beams ≥ 5 m, with markers inserted for particle tracking. We found that: 1) stability increased with test length (Figure 1); 2) collapse was greater at the ends of the beams than in the center (Figure 2 and 3); 3) collapse amplitudes in the longer tests were consistent with the shorter tests and did not reach a constant value (Figure 2); 4) collapse wavelengths in the longer tests were around 3 m, 2X greater than what is predicted by the anticrack model. We conclude that the short tests had greater edge effects than the long tests, and these edge effects decreased stability. Spatial variability in the longer tests also likely increased stability. We suggest that longer tests could be used in addition to shorter tests to reduce false unstable results. We were also able to track collapse amplitude in tests done in the same area over an 11-12 day period. We found an average decrease of 0.65 mm/day due to strengthening of the weak layer. We also experimented with centered PSTs (CPSTs, i.e. notch in the center of the beam), and found that, as predicted by the anticrack theory, the critical length doubled.
Object ID: ISSW13_paper_O5-02.pdf
Language of Article: English
Presenter(s): Unknown
Keywords: crack propagation, extended column test, propagation saw test
Page Number(s): 355-356
Subjects: propagation saw test Extended Column Test (ECT) snow stability
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