Experimental Research on the Effect of Cold Water Injection on the Mechanical Properties and Brittleness of Granite in HDR

To understand the effect of cold water injection on the mechanical properties and brittleness of rock, a series of mechanical tests were performed on granite samples. Firstly, granite samples were slowly heated to a series of target temperatures and then rapidly cooled down using flowing water. Thereafter, optical microscopic observation and uniaxial/triaxial compression tests were performed. Based on the experimental results, the thermal effect on brittleness was further analyzed. Experimental results show that numerous thermally-induced micro cracks were obviously generated when the thermal treatment levels were higher than 300 °C. The variation of mechanical parameters under compression showed a transition from thermal hardening to thermal cracking at 300 °C. The uniaxial compressive strength and Young's modulus significantly decreased only when the thermal treatment levels were higher than 300 °C. Meanwhile, significant energy dissipation was observed prior to the appearance of peak stress. The energy-based brittleness evaluation result shows that the brittleness of granite slightly increased before 300 °C, which followed by sharply decreasing due to the generation of thermally-induced micro cracks. These experimental results may provide references for the thermal effect on the mechanical properties of granite during the exploitation of HDR.