Study on Dual-Mode Instability Characteristics of Layered Snow Slabs Under Different Loading Angles

Weak-layer failure plays an important role in layered snow-slab instability, but how loading-angle-induced changes in the balance between normal and shear loading affect damage evolution and failure behavior remains insufficiently understood. Informed by avalanche surveys along highways in Altay, Xinjiang, this study combines laboratory tests with PFC discrete element simulations to examine layered snow-slab responses at selected loading angles between 0° and 180°. The simulations show an asymmetric variation in mechanical response with loading angle. The low-angle conditions (0–45°) exhibit relatively high structural stiffness and load-bearing capacity. Under nominal shear loading at 90°, peak stress decreases to 1710 Pa, with a peak strain of approximately 0.014. Numerical AE events accumulate progressively under low-angle loading and increase more sharply near failure at 90°. At the particle scale, low-angle loading is associated with mixed compression–shear fractures and continued force-chain reorganization, whereas the 90° condition exhibits concentrated fracture activity and rapid degradation of the load-bearing network. These results identify progressive and abrupt instability characteristics under the model and loading conditions examined and provide insight into the influence of loading direction on failure in layered snow.