Soft and Hard Slab Snow Dynamic Response to Explosives Used in Avalanche Hazard Mitigation

Abstract

Avalanche mitigation routinely uses explosives to both initiate avalanches and test slope stability. This project aimed to verify past findings and further develop an understanding of explosive shockwave interactions with hard and soft slab conditions within 2–5 m of the detonation. Pentolite cast boosters (0.9 and 0.45 kg) were detonated at 0.0, 0.5, 1.0, 1.5, and 2.0 m above the snow. Six orthogonally paired accelerometers inserted into the snowpack recorded snow accelerations. High-pressure sensors located at and above the snow surface measured air overpressures. Distances were scaled to trinitrotoluene (TNT) equivalents to aid in explosive placement comparisons. A substantial advantage was recorded in snow accelerations attributable to elevating explosives above the snow surface. Elevating charges not only increased overall response, but also increased the effective range and depth with no penalty in shock attenuation rates. Using attenuation relationships, a method for predicting the maximum range and affected volume for a specified acceleration value was developed. Field data showed the importance of explosive placement and how the affected volume, and thereby the probability of artificial avalanche release, can be greatly increased.