ABSTRACT. Using a direct simple-shear apparatus, snow samples (llS mm in diameter, 16~ 18 mm in height) taken from a so-called homogeneous layer (small rounded particles, density: 290 kg m -3) were tes~ed in a cold laboratory. Experiments were performed for strain rates between 7 x lQ-6 s-I and 5 x lQ-3 s lat test temperatures of ~5°C, ~ IO D C and ~ 15 D C. The efiects 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 I x 10-3 S-l 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.

ABSTRACT. Measurements of the mechanical properties of snow are essential for improving our understanding and the prediction of snow failure and hence avalanche release. We performed fracture mechanical experiments in which a crack was initiated by a saw in a weak snow layer underlying cohesive snow slab layers. Using particle tracking velocimetry (PTV), the displacement field of the slab was determined and used to derive the mechanical energy of the system as a function of crack length. By fitting the estimates of mechanical energy to an analytical expression, we determined the slab effective elastic modulus and weak layer specific fracture energy for 80 different snowpack combinations, including persistent and nonpersistent weak snow layers. The effective elastic modulus of the slab ranged from 0.08 to 34 MPa and increased with mean slab density following a power-law relationship. The weak layer specific fracture energy ranged from 0.08 to 2.7 J m −2 and increased with overburden. While the values obtained for the effective elastic modulus of the slab agree with previously published low-frequency laboratory measurements over the entire density range, the values of the weak layer specific fracture energy are in some cases unrealistically high as they exceeded those of ice. We attribute this discrepancy to the fact that our linear elastic approach does not account for energy dissipation due to non-linear parts of the deformation in the slab and/or weak layer, which would undoubtedly decrease the amount of strain energy available for crack propagation.

No abstract

No abstract

ABSTRACT. For more than 30 years the quantitative method of evaluating stability (e.g. Roch, 1966; Fohn, 1987;Jamieson, 1995;Jamieson andJohnston, 1998a) has been focused on calculation ora strength-to-load ratio (or stability index): when the shear stress applied to the weak layer reaches the shcar strength, failure is imminent. Howcver, field observations combined with experience and measurements indicate that snow-slab temperatures and slab hardness can have a strong inLluenceon dry-snow slab stability. In this paper, we present a simple static analysis of the stability index, and discuss the importance of slab temperatures and hardness and macroscopic size effects (factors not contained in the stability index) on snow-slab stability. Our conclusion is that the traditional mcthod lacks some elements which arc very important in snow-slab stability, particularly when skier triggering is involved.