Microstructure-based modelling of snow mechanics: experimental evaluation on the cone penetration test

Abstract. Snow is a complex porous material presenting various microstructural patterns. This microstructure controls the mechanical properties of snow, and this control still needs to be better understood. Recent numerical developments based on three-dimensional tomographic data have provided new insights into snow mechanical behaviour. In particular, the discrete element method combined with the snow microstructure captured by tomography and the mechanical properties of ice has been used to reproduce the brittle properties of snow. However, these developments lack experimental evaluation so far. In this study, we evaluate a numerical model based on the discrete element method with cone penetration tests on centimetric samples. This test is commonly used to characterise the snowpack stratigraphy but also brings into play complex mechanical processes and deformation patterns. We measured the snow microstructure on different samples before and after a cone penetration test with X-ray tomography. The cone test was conducted with the Snow MicroPenetrometer (5 mm cone diameter), which recorded the force profile at high resolution. The initial microstructure and the ice properties fed the model, which can reproduce the exact same test numerically. We evaluated the model on the measured force profile and the displacement field derived from the difference between the initial and final microstructures. The model reasonably reproduced the force profiles in terms of average force, force standard deviation, and the correlation length of the force fluctuations. When the contact law describing ice mechanics is adjusted in the range of reasonable values for ice, the agreement becomes good on all three parameters. The model also well reproduced the measured deformation around the cone tip, which is less sensitive to the contact law parameterization. Overall, the model is capable of distinguishing the different microstructural patterns tested. Therefore this confrontation of numerical results with experimental measurements for this configuration gives confidence in the reliability of the numerical modelling strategy. The model could be further applied with different boundary conditions and used to characterise the mechanical behaviour of the snow better.