In order to understand the deterioration of physical and mechanical properties of high-temperature rocks

and the related microscopic characteristics after water-cooling during the thermal reservoir construction

uniaxial compression tests were conducted on five groups of granite samples

which at normal temperature and 200

400

600

and 800 ℃ had experienced water-cooling shocks

respectively. Ultrasonic testing

XRD and polarizing microscope observation were adopted to analyze the microscopic failure mechanics of rocks. Results show that with the increase of rock temperature

the peak strength decreases gradually with an increase of the peak strain

and the failure mode changes from sudden brittle failure to progressive failure. The mass loss rate

volume expansion rate

and density reduction rate increase with the increase of temperature

except for the ultrasonic wave velocity. The volume expansion rate of cooled rock samples increases significantly when the temperature ranges from 400 ℃ to 600 ℃

and the attenuation rate of wave-velocity of rock samples decreases when the temperature ranges from 600 ℃ to 800 ℃. It is found that the larger the temperature gradient

the more the transgranular cracks form due to the water-cooling shocks. A large number of transgranular and intergranular cracks cause the failure modes of rock samples under uniaxial compression to change from tension-shear failure to shear dominant failure accompanied by a large amount of powdery debris.