Laboratory experiments on shear failure of snow

Using a direct simple-shear apparatus, snow samples (115 mm in diameter, 16-18 mm in height) taken from a so-called homogeneous layer (small rounded particles, density: 290 kg m(-3)) were tested in a cold laboratory. Experiments were performed for strain rates between 7 x 10(-6) s(-1) and 5 x 10(-3) s(-1) at test temperatures of -5 degrees C, -10 degrees C and -15 degrees C. The effects of strain rate and temperature on failure stress, failure strain, stiffness (initial tangent modulus) and toughness were studied. The transition between the ductile and brittle (sudden fracture) state of failure was found to be at about 1 x 10(-3) s(-1) for the snow types tested, independent of temperature. Stiffness proved to be the most temperature-dependent property of alpine snow. It strongly increases with decreasing temperature. Failure strain and toughness decrease with decreasing temperature. Failure stress was found to increase slightly with decreasing temperature. The effect is not very distinct but close to statistically significant and might be partly hidden by the scatter in the stress data due to variations inherent in sampling and testing.