Investigation of snow sintering at microstructural scale from micro- penetration tests

摘要

Snow sintering is investigated at microscopic and macroscopic scales with high-resolution cone penetration tests. In a cold room at -10 degrees C, vertical profiles of penetration force were measured periodically during 24 h using the SnowMicroPenetrometer in four snow samples, which differed only by their grain sizes. We estimated the evolution of snow micromechanical properties, namely the bond rupture force, the deflection at rupture and the number of ruptures per penetration increment, by applying a statistical analysis to penetration profiles. The upper part of the profiles is transient due to the progressive formation of a compaction zone in front of the cone tip. In order to explicitly account for this process in the statistical analysis, we used a non-homogeneous Poisson shot noise model which considers a depth dependency of the rupture occurrence rate. On simulated transient profiles, this analysis is shown to provide accurate estimates of the micromechanical properties. On our experimental data, the method effectively revealed that the vertical heterogeneity of penetration force was essentially due to variations of the rupture rate. Conversely, the time evolution of the macroscopic force was mainly due to microstructural bond strengthening. Both macroscopic force and bond rupture force followed a power law with an average exponent of 0.27 and 0.29, respectively. On our samples, a higher exponent for larger grains was observed on the microscopic bond force, while no trend with grain size was visible in the exponent characterizing the macroscopic force evolution.