The Effectiveness of Boot Packing for Snowpack Stabilization

Depth hoar is a persistent weak layer that is a common instability problem in the snowpack of many areas around the world. Boot packing or compaction via explosives is a technique that is widely used in an attempt to disrupt this weak layer and increase its variability across a slope, thereby increasing overall slope stability. While some data have been gathered on the results of boot packing and explosive use on slopes, no recent work has concentrated directly on the effect of boot packing on layer density, hand hardness and stability test scores. Therefore, we devised an experiment to test the changes in these metrics directly on a side-by-side boot-packed and non-boot packed slope. A 50m x 25m, relatively uniform slope was split into two equal areas with one being extensively boot- packed, while the other remained undisturbed. Observations were made in both boot packed and non- boot packed plots until both areas were unreactive with respect to results using Extended Column Tests (ECT) on this basal layer. Our results show that density and hand hardness increased in the boot packed area in comparison to the non-boot packed area. Furthermore, in the boot packed area we also observed a marked increase in ECT scores and a change in fracture character of the basal layers. In the non-boot packed area our ECTs propagated (ECTPs) for a full nine weeks longer than in the boot packed area. While this is just one case study, we are encouraged by our results, which provide quantitative data that indicate that boot packing can be an effective tool for helping to stabilize persistent basal weak layers.