Shear strength and angle of repose of snow layers including graupel

Abstract

AbstractSnow avalanches with failure layers including graupel are sometimes observed in Japan. A snow layer including graupel may be formed close to the melting point (0°C) after passage of a cold front with cumulus clouds. Graupel particles have a large diameter and a spherical shape, so they have a relatively small contact area per unit volume and may form weak layers within the snowpack. In this paper, characteristics of snow layers that include graupel are described by angle of repose, shear frame index (SFI), grain-size distribution, density and temperature. The mean value of the angle of repose was found to be 45°, independent of the grain-size. This suggests that a graupel layer near 0°C will not be formed on a slope exceeding 45°. SFI data for three different graupel layers were measured over 1–3 days for each layer, and were correlated with density. An exponential relationship between shear strength and density was found. The results indicate that the SFI of graupel layers is approximately one-third that of dry new snow with the same density.