Investigation on the damage characteristics and constitutive model of granite under the combined action of temperature and chemical salt solutions

Deep geological disposal repositories are regarded as the most effective and feasible solution for nuclear waste disposal. During the long-term storage process, the surrounding rock in the repository is exposed to high temperatures and hydrochemical environment of varying pH. To study the combined deterioration effect of high temperature and chemical corrosion on the mechanical properties of the surrounding rock of the disposal repository, this paper investigated the physical and mechanical properties of granite after high-temperature damage and chemical salt solutions treatment through uniaxial compression and AE experiments. A statistical damage constitutive model considering the combined initial damage due to heat and chemical effects and micro-element fracture damage during loading was established. At the same time, AE energy was introduced to characterize the damage degree. The results show that high temperature and the action of chemical salt solutions lead to a significant decrease in the quality and wave velocity of granite, as well as a reduction in the crystallinity of the minerals and a tendency for the crystalline structure to become looser. This results in a weakening of the brittle characteristics in the macroscopic mechanical properties of granite. High temperatures and chemical salt solutions reduce the compressive strength and elastic modulus of granite. 400 °C is the threshold for the effect of temperature. When the temperature effect exceeds 400 °C, the compressive strength of the rock drops sharply, and the rock failure changes from brittle deformation to plastic deformation. The established damage constitutive model can effectively describe the failure process of granite under axial loading after thermal-chemical damage. The theoretical stress–strain curve of the model is in good agreement with the experimental curve in terms of the trend, which verifies the validity and applicability of the model.