Thermal Damage in Crystalline Rocks: The Role of Heterogeneity in Mechanical Performance and Fracture Mechanisms

ABSTRACT: Investigating thermally treated rocks' mechanical properties and failure processes is crucial for advancing geothermal energy storage and extraction technologies. Naturally occurring rocks typically exhibit inherent flaws and fractures. Nevertheless, existing studies on the impact of thermal treatment on rock damage predominantly utilize intact rock specimens, either through numerical simulations or experimental approaches. This research introduces the Grain-Based model (GBM) to represent the complex shapes of mineral grains accurately and incorporates the heterogeneity of grain sizes. By employing the Weibull distribution, the model captures the variability in rock internal strength due to microcracks, porosity, mineral composition, and other factors. Furthermore, it integrates the temperature dependency of rocks' physical and mechanical properties when subjected to elevated temperatures, the numerical simulation reproduced the phenomenon that the compaction stage of the stress-strain curve caused by thermal damage extends as the temperature rises. Overall, this study provides a complete understanding of the thermal effects on rock integrity. 1. INTRODUCTION Rocks in nature commonly contain defects such as joints, fissures, and structural planes, which have a decisive impact on the mechanical behavior and stability of the rocks. Particularly under conditions of high temperature, the mechanical properties and failure mechanisms of rocks with such defects can vary significantly from those observed at room temperatures, thus impacting the safety and reliability of rock engineering projects. In geological engineering, nuclear waste storage, and geothermal energy development, rocks are routinely subjected to high-temperature environments. Temperature variations can intensify the expansion of internal defects in rocks, modify their mechanical attributes, and trigger new failure modes. As a quintessential crystalline rock, granite possesses a markedly heterogeneous internal structure. This heterogeneity leads to unique thermal stress responses and failure mechanisms under high temperature and stress conditions, which are significantly different from those observed in homogeneous materials. The non-uniform thermal expansion can result in substantial stress concentration within the rock, facilitating the initiation and propagation of cracks. This process, in turn, impacts engineering structures' long-term performance and reliability.