Role of Ice Mechanics on Snow Viscoplasticity

The porous structure of snow becomes denser with time under gravity, primarily due to the creep of its ice matrix with viscoplasticity. Despite investigation of this behavior at the macroscopic scale, the driving microscopic mechanisms are still not well understood. Thanks to high-performance computing and dedicated solvers, we modeled snow elasto-viscoplasticity with 3D images of its microstructure and different mechanical models of ice. The comparison of our numerical experiments to oedometric compression tests measured by tomography showed that ice in snow rather behaves as a heterogeneous set of ice crystals than as homogeneous polycrystalline ice. Similarly to dense ice, the basal slip system contributed at most, in the simulations, to the total snow deformation. However, in the model, the deformation accommodation between crystals was permitted by the pore space and did not require any prismatic and pyramidal slips, whereas the latter are pre-requisite for the simulation of dense ice. Knowledge of snow settlement is essential for many applications, such as paleoclimatology and avalanche forecasting. Snow densification is mainly driven by time dependent and irreversible deformations. Simulating this highly nonlinear behavior for intricate microstructures is time-consuming, leading to a scarcity of studies and a limited understanding of the underlying microscale mechanisms. In this study, we took advantage of an advanced numerical solver to calculate the behavior of 3D imaged snow samples and compared it with in situ experiments. Our analysis has shown that the crystalline structure must be taken into account, but the discrepancy between experiments and simulations suggests the existence of other mechanisms, particularly between snow grains. Interestingly, deformation mechanisms other than those required to simulate dense ice have been observed. Ice in snow cannot be considered as homogeneous, individual crystals are shown to impact snow creep The models shows that basal glide of a few ice zones supports most of the snow deformation In the simulations, the contribution of the hard slip systems is negligible, and deformation accommodation is enabled by the pore space