The Extended Column Test: Test effectiveness, spatial variability, and comparison with the Propagation Saw Test

Abstract

The Extended Column Test (ECT) is a new stability test that aims to assess the fracture propagation potential across a 90 cm wide isolated column. Initial results with a dataset consisting of over 300 tests collected by one observer demonstrated the ECT's effectiveness for differentiating between stable and unstable slopes. Further, we have received positive feedback on the test from a world-wide network of observers. This paper: 1) presents new recording standards for the test, 2) uses the SnowPilot dataset to further assess the effectiveness of the test by analyzing over 300 tests performed by several observers in different snow climates, 3) looks at the spatial variability of ECT results from several test grids, and 4) compares side-by-side results between the ECT and the Propagation Saw Test on stable and unstable slopes. Our results indicate that the ECT is an effective stability test, with a false stability ratio generally less than other standard snow stability tests. Results are sometimes quite spatially uniform, though occasionally slopes may exhibit variable ECT results. In comparison to the PST, our data suggest the ECT has a lower false stability rate, but a higher false instability rate. No test is perfect and all tests must be used in conjunction with additional data, but our results show the ECT is valuable additional tool for assessing snow stability.

The influence of edge effects on crack propagation in snow stability tests

“…For specifics on the particle tracking methodology, see previous work on particle tracking with stability tests (van Herwijnen and Jamieson, 2005;van Herwijnen and Heierli, 2009;van Herwijnen et al, 2010;Bair et al, 2012;. Similar to another study , we found it was often not possible to track particles near the shovel during ECTs because of snow compaction under the shovel.…”

“…The selected tests had similar collapse amplitudes a (3-9 mm) to those in other studies of failures on persistent weak layers (van Herwijnen and Jamieson, 2005;van Herwijnen et al, 2010;. Plotting horizontal position against collapse amplitude shows that a steady state was not reached, even after almost 7 m (Fig.…”

“…For instance, the longest crack propagation length recorded in previously published studies has been about 3 m (van Herwijnen and Jamieson, 2005;Gauthier and Jamieson, 2008;van Herwijnen et al, 2010;. Also, cracks likely propagate radially from a trigger in an avalanche, while in PSTs and ECTs, cracks are forced to travel in a straight path.…”

“…The standard beam length for ECTs and PSTs is about 1 m. Technically, ECT guidelines suggest 0.9 m (Simenhois and Birkeland, 2009), while PST guidelines (Gauthier and Jamieson, 2008) suggest the greater of 1.0 m or the height of the slab. These length guidelines have not been rigorously evaluated in terms of how the stress field is affected by test length.…”

“…We therefore excluded two tests (a 6 m ECT on 13/03 and a 6 m PST on 14/03, Table 1) which fully propagated but then slid downhill. In tests that slide downhill, the collapse phase cannot be distinguished from the continuous bed surface erosion process (van Herwijnen and Jamieson, 2005). We also selected particle tracking results from 3 m tests that were done side by side to the longer tests for comparison.…”