Experimental investigation of interactions between explosive detonations and the resulting snowpack response

Abstract

Avalanches threaten many areas of the world. For many years, risk has been mitigated through artificial avalanche initiation using explosives. Even with extensive use, a lack of experimental determinations of the interactions between explosive detonations and the snowpack response exists. To address this, a multiyear field based research project was conducted at Montana State University, Bozeman, MT. A portable instrument array consisting of pressure and accelerometer sensors was fabricated and utilized to record the overpressure and acceleration of the snowpack resulting from detonation of pentolite cast boosters. Explosives were detonated 0-2 m above the snow surface, at 0.5 m increments. All sensors were placed within a 7 m radius of the explosive in soft slab and hard slab snow conditions. The data was used to characterize relationships between explosive size and location to the resulting overpressure and snow acceleration based on various snow parameters. The snow surface was shown to be able to reflect shockwaves, thus, increasing the shockwave pressure. It was shown that elevating an explosive off the snow surface resulted in greater overpressure and peak snowpack acceleration than surface detonations. Elevating an explosive was found to not influence the vertical or radial attenuation. Therefore raising a charge increased the volume of influence. Overpressure and acceleration were shown to be nonlinearly related to the explosive mass. Doubling the mass resulted in less than double the response. The acceleration of moist snow was determined to be less and the attenuation greater than for dry snow conditions. Hard slab conditions indicated lower acceleration and greater shockwave attenuation than soft slab snow. Snowpack peak acceleration and attenuation were shown to have little dependence on either the total snow water equivalent or snow density. For rock bed surfaces the shockwave was reflected back through the snow while meadow bed surfaces did not. This project verified past theoretical and experimental results, but further research would be beneficial for avalanche mitigation work. A continuation of this work could lead to increased efficiency and safety for the avalanche community.