Abstract
Abstract. The Extended Column Test (ECT) and the Propagation Saw Test (PST) are two commonly used tests to assess the likelihood of crack propagation in a snowpack. Guidelines suggest beams with lengths of around 1 m, yet little is known about how test length affects propagation. Thus, we performed 163 ECTs and PSTs 1.0–10.0 m long. On days with full crack propagation in 1.0–1.5 m tests, we then made videos of tests 2.0–10.0 m long. We inserted markers for particle tracking to measure collapse amplitude, propagation speed, and wavelength. We also used a finite element (FE) model to simulate the strain energy release rate at fixed crack lengths. We find that (1) the proportion of tests with full propagation decreased with test length; (2) collapse was greater at the ends of the beams than in the centers; (3) collapse amplitude was independent of beam length and did not reach a constant value; (4) collapse wavelengths in the longer tests were around 3 m, two times greater than what is predicted by the anticrack model. We also confirmed the prediction that centered PSTs had double the critical length of edge PSTs. Based on our results, we conclude that cracks propagated more frequently in the shorter tests because of increased stress concentration from the far edge. The FE model suggests this edge effect occurs for PSTs of up to 2 m long or a crack to beam length ratio ≥ 0.20. Our results suggest that ECT and PST length guidelines may need to be revisited.
Highlights
Snow stability tests are used to evaluate avalanche hazard
We find that cracks in shorter tests are more prone to influence from the far edge than in longer tests, and this edge effect causes them to fully propagate more often
We suggest that Extended Column Test (ECT) and Propagation Saw Test (PST) length guidelines be revisited
Summary
Snow stability tests are used to evaluate avalanche hazard. Based on SnowPilot pit data across the US over the last decade (Birkeland and Chabot, 2012), the three most popular tests are, in this order: (1) the Extended Column Test (ECT), (2) the Compression Test (CT), and (3) the Propagation Saw Test (PST). The PST has similar dimensions to the ECT, but the beam is loaded by creating a progressively longer notch in the weak layer with the blunt end of a snow saw. In field and laboratory fracture tests, edge effects are always present. The crack nucleus in both tests can be considered a through crack, meaning that the crack extends from one side to the other This obviously does not model a crack nucleus in an avalanche, which is an embedded crack; that is, a crack nucleus far from any edges. It may be possible to use a beam that is significantly wider than a shovel in an ECT to reduce this edge effect, but we are not aware of any studies which have done this
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