Force measurements during snow stability tests

A very powerful and commonly used method to assess the danger of avalanche release on a slope is the performance of snow stability tests. The present work aims to contribute towards a better understanding of snow stability test results by conducting force measurements during a snow stability test, namely the Compression Test (CT). We were particularly interested in the variability of the force applied to a potential weak layer during the test by different persons and for different snow covers. We therefore focused on the stress levels for the single taps and loading steps of a CT, and how they were influenced by different snow properties (effective depth, compaction depth, and snow hardness) as well as other factors, such as test subjects’ body weight and arm length. We used two capacitive pressure sensors to conduct force measurements during the performance of CTs at two different depths with eleven different people and at seven different locations. The evaluation and analysis of these measurements were conducted with Python. Our results showed that the penetration depth and compaction of the snow above the force sensor significantly influenced the transmission of stress. The stress levels of shoulder taps were in the range of stress levels below a standing skier and decreased non-linearly with penetration depth. Furthermore, we found that stress levels were rising also within distinct loading steps. Moreover, it was possible to confirm the influence of a person’s weight and arm length on stress levels, and consequently, statistically significant differences between different test persons. In terms of avalanche safety, our results indicate a non-linear decrease of the probability of fracture initiation with increasing tap number. Most importantly, we discovered that regardless of what was analysed, the data’s scattering decreased with increasing depth, which means that the significance of a CT result increased considerably with increasing fracture depth.