Thermo-mechanical Coupling Characteristics of Granite under Triaxial Pressures and Ultrahigh Heating Rates

Understanding thermo-mechanical behavior of granite under triaxial stress and ultrahigh heating rates is essential for advancing the flame-assisted drilling technique in geothermal systems. To address the challenge of real-time crack observations at high temperatures, we have developed a finite difference model that replicates grain-scale heterogeneities and incorporates a modified strain-softening law of granite subjected to various triaxial pressures (ranging from 10 to 90 MPa) and temperatures (from 25 to 300 degree celsius). Using the calibrated model, we investigated the thermo-mechanical coupling mechanism of granite under high temperatures and triaxial pressures, along with the impact of ultrahigh heating rates (up to 600 degree celsius/min) through a series of numerical simulations. Our simulation results, supported by laboratory observations, reveal that the combined effects of sample dimensions, heating rates, and confining pressures intricately shape the resulting patterns of cracking and internal structural modifications in the samples. Among the studied factors, confining pressure plays a central role in influencing thermal-induced cracking behaviors, contributing to the modification of crack patterns. These findings provide a fundamental understanding that can help address challenges related to thermal-assisted rock breaking techniques, thus holding great significance for the new and efficient well construction technologies in geothermal engineering.