Microcracking behavior and damage mechanism of granite subjected to high temperature based on CT-GBM numerical simulation

Studying the high-temperature impact on microcracking behavior of granite is of great significance to geothermal energy extraction and deep engineering disaster prevention. Therefore, a thermo-mechanical coupled numerical model of granite is established based on computed tomography and grain-based model (CT-GBM) to investigate the impact of high temperature upon microcracking behavior of granite, and to further discuss the thermal damage mechanism. The results show that the thermal damage of granite mainly develops in the form of tensile failure. The development of intra grain cracks can be roughly divided into three periods featuring quiet (room temperature ∼ 300℃), stable development (300℃∼450℃) and unstable development (450℃∼600℃). The development of grain boundary cracks first appeared at the feldspar-quartz grain boundary, but the feldspar-feldspar grain boundary cracks prevail at high temperature (above 332℃) due to the large proportion of feldspar in granite. The phenomenon of stress concentration in granite under high temperature becomes growingly obvious with the increase of temperature, and such phenomenon is more obvious in grain boundaries than in mineral grains, which is the reason of microcracking and prevail of grain boundary cracks. In addition, the thermal damage degree of mineral grains and grain boundaries is described quantitatively through the self-defined crack coefficient. It is discovered that under the joint influence of thermal expansion characteristics and mechanical properties of minerals, the damage of grain boundaries between different minerals is more serious than that in identical minerals, and the damage of quartz grain is more serious than that of feldspar and mica.