The study of alterations in rock mechanical properties as a function of thermal damage is relevant to various engineering applications, such as nuclear waste repository, underground coal gasification, dry fracture shale system, and geothermal energy extraction. The mechanical behavior of reservoir rock is significantly influenced by the elevated temperatures, since the status of micro-structure of the rock mass is controlled by thermal expansion, newly-generated micro-cracks, dilation of existing micro-cracks, and various mineralogical alterations. Rock yield strength is generally positive with the elastic modulus, cohesive strength and friction angle, while it decreases with temperature increasing.
The following defines a novel thermal-mechanical-damage coupled model accommodating the interaction of thermal conductivity, thermal-induced deformation and rock mechanical deformation and damage to define the changes in rock thermal and mechanical properties during thermal treatment. Importantly, we developed a dual-damage constitutive model for elastic modulus and strength respectively, to solve the problem of the non-synchronous changes in peak strain and peak strength, which is induced by its thermal damage. The proposed model is validated by the laboratory data.
The results indicate that thermal-induced damage has a significant effect on rock physical and mechanical properties-increases rock porosity and permeability and decreases rock elastic modulus and strength. Furthermore, it is confirmed that the thermal-induced damage is dominated by tensile damage of rock during the thermal expansion. The proposed dual-damage constitutive model better explains the changes of peak strain and peak strength observed in experiments.
Thermal-induced rock damage plays a vital role for various engineering applications, such as nuclear waste repository, underground coal gasification, dry fracture shale system, geothermal energy extraction, and deep mining (Cai and Brown, 2017; Heap et al., 2011; Shao et al., 2015; Shoko et al., 2006; Tsang, 1999). Therefore, it is of great significance to understand alterations of rock mechanical properties induced by thermal damage for the design and safety assessment in deep underground rock engineering.