Beam Theory Applied to Slab Avalanche Release

Abstract:

Slab avalanches are the most destructive form of avalanche and are difficult to predict, in part because of a mixed-mode failure of a weak layer beneath a snow slab. Slab bending prior to slab fracture may play a critical role in propagating a fracture through a weak layer during slab avalanche release. Due to the catastrophic, dangerous, and unpredictable nature of avalanches, the deformation of a snow slab is difficult to measure at the onset of an avalanche. Therefore, field-based snow stability tests, such as the Propagation Saw Test, provide insight into the dynamics of slab avalanche release. Beam theory provides analytical models to describe the slab deformation during such a test. In the last 8 years, at least three separate research groups have published their application of beam theory to slab deformation, yet many questions remain. Furthermore, because these models vary in their assumptions related to shear deformation, weak layer response, and boundary conditions, they are not easily compared to one another. Presented here, is a critical review of these previous works and a unified extension of these models. From Timoshenko beam theory, the inclusion of shear deformation yields an important modeled output of shear stress in an anisotropic weak layer during different loading schemes of a Propagation Saw Test. Shear stress in the weak layer is a critical variable for a slab avalanche release model because shear failure in the weak layer has been shown to precede collapse in many laboratory tests. This review, analysis, and extension of modeling slab deformation provides insight and utility for the development of avalanche release models.