Basal shear and normal stresses of dry and wet snow avalanches after a slope deviation

Abstract

Basal shear and normal force measurements of dry and wet snow avalanches and slush flows from the Weissfluhjoch snow chute are presented. This chute contains two slope angle transitions in order to measure the effect of slope deviations on the normal and shear force distributions. Slope deviations are typically encountered near snow sheds and the dynamic forces resulting from them must be considered in the structural analysis. A total of 42 experiments were performed and the coefficient of sliding friction was determined. We found that the coefficient of friction varied between wet, dry and slush flows and was, in general, higher than the value suggested by the Swiss guideline for snow shed design. A velocity dependent friction could not be identified. The Swiss guideline formulas to calculate shear and normal forces after a slope deviation do not agree with our measurements. Near the deviation, the formulas underestimate the applied forces; far from the deviation, they overestimate the forces. Because flow velocities were measured, the energy dissipation rates of the events could be determined. We found that dry and wet snow slides dissipate most of their energy at the basal layer.