Thermo-mechanical behavior and microcrack evolution of vein-bearing granite simulated with a moment-tensor-enhanced 3D TM-GBM

Understanding the thermo-mechanical behavior and damage mechanisms of vein-bearing granite is essential for high-temperature underground engineering. In this work, a moment-tensor-enhanced three-dimensional thermo-mechanical grain-based model (3D TM-GBM) was developed in PFC3D to characterize the mechanical response and microcrack evolution of vein-bearing granite. The model explicitly reproduces feldspar, quartz, mica grains, quartz veins and vein-matrix interfaces. Linear parallel-bond and smooth-joint models were used for intragranular contact and mineral boundaries and vein-matrix interfaces, respectively. Mineral-specific thermal properties and interparticle thermal pipes were incorporated to simulate heterogeneous heat transfer and thermally induced deformation. On this basis, a twelve-category scheme classified tensile and shear fractures across different intragranular and intergranular contacts. Additionally, the moment-tensor method was used to identify tensile, shear, and press-shear AE source mechanisms. The proposed model was calibrated and validated against laboratory stress-strain responses, peak strength, mineral composition, and fracture characteristics. Subsequently, the effects of thermal-treatment temperature and vein inclination on the thermo-mechanical damage evolution of vein-bearing granite were investigated using the 3D TM-GBM model. Results show that thermal-expansion mismatch and interfacial sliding jointly govern crack localization, force-chain reorganization, and strength degradation. This work provides an effective numerical approach for investigating mineral-scale thermo-mechanical damage in heterogeneous vein-bearing rocks.