EGU21-8253
https://doi.org/10.5194/egusphere-egu21-8253
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

From sub-Rayleigh to intersonic crack propagation in snow slab avalanche release

Bertil Trottet1, Ron Simenhois2, Gregoire Bobillier3, Alec van Herwijnen3, Chenfanfu Jiang4, and Johan Gaume1,3
Bertil Trottet et al.
  • 1Snow and Avalanche Simulation Laboratory (SLAB), Swiss Federal Institute of Technology (EPFL), CH-1015 Lausanne, Switzerland
  • 2Colorado Avalanche Information Center, Boulder, CO, USA
  • 3WSL Institute for Snow and Avalanche Research SLF, CH-7260 Davos, Switzerland
  • 4Computer and Information Science Department, University of Pennsylvania (UPenn), PA-19104 Philadelphia, USA

Snow slab avalanche release can be separated in four distinct phases : (i) failure initiation in a weak snow layer buried below a cohesive snow slab, (ii) the onset and, (iii) dynamic phase of crack propagation within the weak layer across the slope and (iv) the slab release. The highly porous character of the weak layer implies volumetric collapse during failure which leads to the closure of crack faces followed by the onset of frictional contact. To better understand the mechanisms of dynamic crack propagation, we performed numerical simulations, snow fracture experiments, and analyzed the release of full scale avalanches. Simulations of crack propagation are based on the Material Point Method (MPM) and finite strain elastoplasticity. Experiments consist of the so-called Propagation Saw Test (PST). Concerning full scale measurements, an algorithm is applied to detect changes in image pixel intensity induced by slab displacements. We report the existence of a transition from sub-Rayleigh anticrack to supershear crack propagation following the Burridge-Andrews mechanism. In detail, after reaching the critical crack length, self-propagation starts in a sub-Rayleigh regime and is driven by slab bending induced by weak layer collapse. If the slope angle is larger than a critical value, and if a so-called super critical crack length is reached, supershear crack propagation occurs. The corresponding critical angle may be lower than the weak layer friction angle due to the loss of frictional resistance during volumetric collapse. The sub-Rayleigh regime is driven by mixed mode anticrack propagation while the supershear regime corresponds to a pure mode II propagation with intersonic crack speeds (v: crack speed, cs: shear wave speed, cp: longitudinal wave speed, E: slab Young's modulus and ρ: slab density). This intersonic regime of crack propagation thus leads to pure tensile slab fractures initiating from the bottom of the slab as opposed to top initiations induced by slab bending in the sub-Rayleigh regime. Key ingredients for the existence of this transition are discussed such as the role played by friction angle, collapse height and slab secondary fractures. 

How to cite: Trottet, B., Simenhois, R., Bobillier, G., van Herwijnen, A., Jiang, C., and Gaume, J.: From sub-Rayleigh to intersonic crack propagation in snow slab avalanche release, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8253, https://doi.org/10.5194/egusphere-egu21-8253, 2021.

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