Influence of cooling speed on the physical and mechanical properties of granite in geothermal-related engineering

In deep-earth engineering, the high earth temperature can significantly affect the rock's mechanical properties, especially when the rock is cooled during the construction process. Accordingly, whether the cooling speed affects the mechanical and physical properties of rocks is worth to be investigated. The present study explored the influence of the cooling rate on the physical and chemical properties of granite heated at 25-800 degrees C. The mechanical and physical properties involved in this study included uniaxial compression strength, peak strain, modulus, P-wave velocity, mass and volume, the change of which could reflect the sensitivity of granite to the cooling rate. Acoustic emission (AE) monitoring, microscopic observation, and X-ray diffraction (XRD) are used to analyze the underlying damage mechanism. It is found that more AE signals and large-scale cracks are accounted for based on the b-value method when the specimens are cooled by water. Furthermore, the microscopic observation by polarized light microscopy indicates that the density, opening degree, and connectivity of the cracks under water cooling mode are higher than that under natural cooling mode. In addition, the XRD illustrates that there is no obvious change in mineral content and diffraction angle at different temperatures, which confirms that the change of mechanical properties is not related to the chemical properties. The present conclusion can provide a perspective to assess the damage caused by different cooling methods to hot rocks.