Micromechanical modeling of snow failure

Abstract

Abstract. Dry-snow slab avalanches start with the formation of a local failure in a highly porous weak layer underlying a cohesive snow slab. If followed by rapid crack propagation within the weak layer and finally a tensile fracture through the slab, a slab avalanche releases. While the basic concepts of avalanche release are relatively well understood, performing fracture experiments in the laboratory or in the field can be difficult due to the fragile nature of weak snow layers. Numerical simulations are a valuable tool for the study of micromechanical processes that lead to failure in snow. We used a three-dimensional discrete element method (3-D DEM) to simulate and analyze failure processes in snow. Cohesive and cohesionless ballistic deposition allowed us to reproduce porous weak layers and dense cohesive snow slabs, respectively. To analyze the micromechanical behavior at the scale of the snowpack (∼1 m), the particle size was chosen as a compromise between low computational costs and detailed representation of important micromechanical processes. The 3-D-DEM snow model allowed reproduction of the macroscopic behavior observed during compression and mixed-mode loading of dry-snow slab and the weak snow layer. To be able to reproduce the range of snow behavior (elastic modulus, strength), relations between DEM particle and contact parameters and macroscopic behavior were established. Numerical load-controlled failure experiments were performed on small samples and compared to results from load-controlled laboratory tests. Overall, our results show that the discrete element method allows us to realistically simulate snow failure processes. Furthermore, the presented snow model seems appropriate for comprehensively studying how the mechanical properties of the slab and weak layer influence crack propagation preceding avalanche release.

Studying Snow Failure With Fiber Bundle Models

“…the snow viscosity model of Bartelt and von Moos [44], the open-cell foam model for snow [45,46], or other models considering damage healing [3,47,48]. (ii) Models reproducing the microstructure in simplified form with discrete elements (beams, spheres) with some random variations such as the discrete element models [49][50][51]. (iii) Models that use the full 3-D representation of the microstructure obtained by micro-tomography as input for a finite-element model (e.g., [52][53][54]).…”

Micro-mechanical Insights Into the Dynamics of Crack Propagation in Snow Fracture Experiments

“…We developed a 3-D discrete element model to investigate the micro-mechanical processes at play during crack propagation in snow fracture experiments. Microscopic model properties were calibrated based on macroscopic snowpack quantities using the method developed by Bobillier, et al 19 . The field data of a PST fracture experiment was recorded during winter 2019 and analyzed with image correlation techniques 12 .…”

“…To generate the large DEM simulation domain needed to reproduce the experimental PST, we generated a cell under spatial periodic boundary conditions (base, weak layer and slab) 19 . We then replicated and joined multiple cells (9 in total) to obtain the complete PST system.…”

“…These models provided new insight into key parameters and driving forces, however, the micro-mechanical processes involved during dynamical crack propagation are still essentially unknown. While their direct observation is so far not feasible, the Discrete Element Method (DEM) has previously been successfully used to study the influence of snow microstructure on the mechanical behavior of snow [19][20][21][22] and crack propagation in weak layers 16,23 . Therefore, DEM is an appealing method to study the effect of the complex and highly porous snow microstructure on the dynamics of crack propagation, which does not require the assumption of a complex macroscopic constitutive model 3 .…”

Microstructural controls of anticrack nucleation in highly porous brittle solids

“…As aforementioned, the advantage of this approach is that parameters of the Sticky Hard Spheres model (volume fraction and coordination number) can be directly evaluated based on X-ray tomographic images by matching correlation functions 31 . While several recent numerical studies have analyzed the mechanical response of porous brittle solids like snow based on the real samples' microstructures 18,19,21 , it has been recently shown that simplified structures made of spherical particles can be used to reproduce accurately important features of snow mechanics in the brittle range for different processes: failure initiation 35,36 , crack propagation 9,10 , snowflake fragmentation 37 , wind blowing snow 38 , snow granulation 39 and avalanche impact pressures 40 . One the one hand, this simplification makes us loose important information about the microstructure.…”