Crack arrest in dry snow slab avalanches: Assessing the feasibility of man-made structures to stop crack propagation

Large dry snow slab avalanches are responsible for most fatalities in Europe and also affect infrastructure such as roads, railways, ski resorts, and villages worldwide. Several decades of research focusing on crack propagation in weak snow layers have uncovered multiple mechanical processes leading to larger avalanches. A key finding is the transition from anticrack propagation (collapse of the weak layer) to a very fast shear-based propagation regime, in which crack speed can approach the longitudinal wave speed of the slab and is most likely associated with larger avalanches. However, there is still a lack of understanding regarding crack arrest mechanisms and the final propagation extent. Recent studies suggest that crack arrest processes can differ depending on scale related to both propagation regime, as well as crack arrest may or may not involve slab fracture.

This work focuses on large-scale crack arrest in the shear-based propagation regime, involving slab fractures in the cross-slope direction. The practical objective of this study was to test the feasibility of a ridge-like structure oriented in the downslope direction that could potentially promote slab fractures, stop crack propagation, and limit avalanche size during avalanche control operations. We used a numerical method called the Depth-Averaged Material-Point Method (DAMPM), which can reproduce all mechanical processes relevant to large avalanche release. Using this method, we simulated three different slope configurations to study cross-slope propagation in the presence of the ridge-like structure: (1) a simple planar slope 10 m long and 30 m wide, (2) an analytical bowl-shaped slope 120 m long and 80 m wide, and (3) a real, complex 3D terrain of the Stanley Path in Colorado.

For each slope configuration, we added a ridge-like feature where slab thickness—and correspondingly slab strength—was reduced, promoting slab fractures at the structure. Our results show that the structure dimensions are less important than the minimum slab depth covering the structure in discriminating between crack arrest and propagation through the structure. However, near the threshold slab depth value separating arrest from propagation, the structure dimensions—specifically the structure dimension ratio (height over width)—can influence whether arrest or propagation occurs. These results were consistent across all three slope configurations. Finally, simulations on the real 3D complex terrain of Stanley Path show realistic slab fracture behavior over complex topography, including both tensile and compressive fractures. These results contribute to an improved understanding of crack arrest mechanisms involving slab fracture.