Mode II fracture parameters of dry snow slab avalanche weak layers calculated from the cohesive crack model

Release of dry snow slab avalanches starts with shear failure within a thin weak layer beneath a stronger, cohesive slab. The propagating fracture is within the weak layer as mode II. The fundamental fracture properties include the weak layer critical mode II fracture energy and stress intensity factors. In this paper, mode II fracture energy was calculated from the cohesive crack model from dry slab avalanche fracture line data and in-situ shear fracture tests. One advantage of the cohesive crack model is that it does not require the effective elastic modulus which is highly rate dependent and largely unknown in avalanche release. The results gave weak layer mode II fracture toughness less than mode I fracture toughness for the cohesive slab and fracture energy about one order of magnitude less than for solid ice. From the fracture energy and the mode II stress intensity factor, Irwin’s relation enables calculation of the effective elastic modulus. Calculations of the effective modulus for mode II initiation were compared with other estimates and they were shown to be consistent.