A permafrost test on intact gneiss rock

Changes in permafrost conditions in high mountain rocks have increased the risk of dangerous instabilities. Ice segregation within the rock mass has been interpreted as one of the mechanisms involved in high mountain bedrock degradation. A long term laboratory test on a cube of intact gneiss has been designed to reproduce field temperature gradients and water supply conditions. Test results demonstrate that ice crystallization in a permafrost fringe (T=0 °C to −3 °C) leads to the formation of continuous ice-filled cracks which explain the loss of rock continuity and the observed rock failures. A coupled thermo-hydro-mechanical model which incorporates the thermodynamics of ice-water mixtures has been used to reproduce test results. The model, which follows existing formulations for unsaturated porous media, was capable of capturing the main observations derived from the experiment. Calculated tensile stresses are close to the gneiss tensile strength. The analysis performed is a step forward in understanding field observations and in the application of computational tools to real cases.