Frozen soil properties modification in the context of climate change

Abstract

One of the expected effects of global warming is the gradual melting of permanently frozen ground, known as permafrost. The melting of permafrost will significantly impact soil material properties and (pore) fluid flow, potentially causing instability of infrastructures and triggering natural hazards such as landslides, rock falls, or debris flows. The overall objective of this research is to experimentally quantify the effect of thawing on the geomechanical strength of a reconstituted soil. More specifically, it is intended to qualify the initial frozen state and compare it to the state after thawing. The proposed experimental study was carried out in three steps. Firstly, soil samples were identified by the usual parameters such as water content, bulk density, solid particle density, triaxial test etc. Permafrost temperatures recorded by PERMOS and PermaFrance in the Alps (Swiss and French) are of the order of -3 to -4.5°C at a depth of -10m. This is why, for the second step, the shear tests were carried out at a slightly lower temperature than that recorded in situ. Artificial samples were sheared at a temperature of -5°C in our temperature controlled triaxial press in order to determine the soil’s strength parameters (cohesion and internal angle of friction). Thirdly, same tests were carried out at a temperature of +5°C in order to thaw the soil completely before the shearing. In total, three tests for each temperature were compared and discussed. The expected results aim at a better understanding and quantification of soil strength reduction after the thawing phase. As many infrastructures are now built on permafrost, such as roads, ski infrastructures, power lines or alpine chalets, they will be affected by this phenomenon in the near future. A better understanding of (geo)mechanical consequences might facilitate risk analysis, evaluation and mitigation.