Abstract
Snow slab avalanches start with a failure in a weak snow layer buried below a cohesive snow slab. After failure, the very porous character of the weak layer leads to its volumetric collapse and thus closing of crack faces due to the weight of the overlaying slab. This complex process, generally referred to as anticrack, explains why avalanches that release on steep slopes can be triggered from flat terrain. On the basis of a new elastoplastic model for porous cohesive materials and the Material Point Method, we investigate the dynamics of mixed-mode anticracks, the subsequent detachment of the slab and the flow of the avalanche. In particular, we performed two and three dimensional slope scale simulations of both the release and flow of slab avalanches triggered either directly or remotely. We describe the fracture and flow dynamics on a realistic topography and focus on the volumetric plastic strain, stress invariants, propagation speed and flow velocity. Our simulations reproduce typical observations of “en-echelon” fractures and the propagation speed reached up to three times that measured in field experiments. In addition, slab fracture always started from the top in the Propagation Saw Test while it systematically initiated at the interface with the weak layer at the crown of slope-scale simulations in agreement with limited field observations. During the avalanche flow, snow granulation, erosion and deposition processes were naturally simulated and do not need additional implementations. Our unified model represents a significant step forward as it allows simulating the entire avalanche process, from failure initiation to crack propagation and to solid-fluid phase transitions, which is of paramount importance to forecast and mitigate snow avalanches.
Highlights
Snow is a complex material which can sustain stresses like a solid or flow like a fluid depending on the applied loading and strain rate (Louchet et al, 2013)
We observe “en-echelon” types fractures (Gauthier and Jamieson, 2010) i.e. crack propagation in the weak layer is subsequently followed by slab fractures slightly down slope the crack tip, as shown in Fig. 3 in 2D and Fig. A1 in 3D
The model is based on finite strain elastoplasticity and allows to reproduce the complex mechanical behavior of different snow types including weak snowpack layers with a mixed-mode failure followed by strain softening and structural collapse allowing to simulate dynamic anticrack propagation
Summary
Snow is a complex material which can sustain stresses like a solid or flow like a fluid depending on the applied loading and strain rate (Louchet et al, 2013). Slab avalanches can be devastating phenomena of large scale (> 100 m), their release is controlled by failure mechanisms at the microscopic scale (< 1 mm) in the snowpack. Our understanding of the mechanical properties of snow as well as slab avalanche release processes has improved over the last years (Schweizer et al, 2016). This progress is related to modern experimental methods coupled with multiscale models, which were encouraged by the fast increase of computational capabilities. The typical anisotropic microstructure of persistent weak layers leads to lower strengths in shear than in compression (Reiweger and Schweizer, 2010)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
