SHEAR CELL EXPERIMENTS OF SNOW AND ICE FRICTION

Snow and ice friction was investigated with a shear cell in which two surfaces of annular snow and/or ice samples were in contact and sheared by rotation. The temperature ranged from 0 to -25-degrees-C, normal stress from 205 to 1292 Pa, and velocity from 0.9 to 25.3 m/s. The total friction coefficients measured by friction of two hard sintered snow plates ranged roughly from 0.2 to 0.8, which were separated into velocity-independent dry friction and linearly dependent viscous friction; only at velocities larger than 15 m/s did friction increase parabolically, evidence of turbulent friction. The dry friction coefficient (mu-D) was found to consist of Coulomb friction and adhesion, both of which were strongly dependent on temperature and hardness of snow; mu-D decreased linearly with lowering temperature from 0.47 at 0-degrees-C to 0.22 at -25-degrees-C. Viscosity was found to be dependent on snow type (grain characteristics) but independent of temperature; the average kinematic viscosity was roughly 5 X 10(-5) m2/s for snow of density around 350 kg/m3. The total friction coefficient for ice-ice friction was an order of magnitude smaller than that of snow-snow friction, typically less than 0.04; its magnitude increased with velocity but at lower temperatures (e.g., - 35-degrees-C) it decreased exponentially with velocity. The minimum Coulomb friction coefficient as small as 0.008 was observed at -11-degrees-C. All the friction coefficients for snow-snow, snow-ice, and ice-ice friction were summarized in temperature-velocity diagrams, which conveniently show the overall behaviors of snow and ice friction.