Thermo-Mechanical Coupling Analysis Applied to Granite Specimens Subjected to Uniaxial and Triaxial Tests to Investigate Thermal Crack Generation

Granite in the deep crust undergoes long-term high-temperature and high-stress (HTHS) environments, and its mechanical properties are significantly different from those under conventional conditions. Granite is prone to thermal damage under the influence of thermo-mechanical (TM) coupling, resulting in complex nonlinear mechanical responses, which directly affect the stability of deep geotechnical engineering. However, due to the limitations of experimental conditions, TM coupling experiments under HTHS conditions are difficult to carry out effectively, resulting in the dominance of single-factor (temperature or stress alone) research and a lack of systematic analysis under TM coupling. This study employed a combined experimental and numerical approach to obtain the physical properties of granite under conventional conditions and the TM coupling response under HTHS conditions. The results indicate that elevated temperatures induce the formation of thermal cracks in granite, leading to thermal damage. This damage causes a transition in specimen deformation from linear elastic behavior under conventional conditions to plastic deformation. Meanwhile, increasing confining pressure effectively suppresses thermal damage by reducing the generation of thermal cracks. A model to predict how thermal damage affects the strength of granite was created, showing how the mechanical properties of granite change when exposed to thermal and mechanical conditions together. This study addresses the limitations of traditional single-factor experiments, which fail to accurately represent complex geological conditions, and provides a theoretical basis for deep engineering projects.