Abstract: The temperature of cooling medium has a significant influence on the mechanical properties of granite under the thermal shock, which is mainly determined by the number and density of internal cracks that are determined by the thermal shock velocity and thermal shock factor, but have no direct correlation with the temperature difference of thermal shock. In this paper, the self-developed rock thermal shock cracking test apparatus is used to study the evolution of macroscopic mechanical properties (e.g., the uniaxial compressive strength, tensile strength, cohesion and internal friction angle) granites, taken from Gonghe basin, Qinghai province, under thermal shock tests in water with different cooling temperature. The results show that, with the same heating temperature, the uniaxial compressive strength, tensile strength and cohesion of granite decrease with the increase of the cooling temperature, and the internal friction angle increase with the increase of the cooling temperature in water. The compressive strength and tensile strength of granite under thermal shock show a regular deterioration trend with the degree of thermal shock cracking. The compressive strength and tensile strength of granite heated up to 600 ℃ and rapidly cooled in 100 ℃ water, is only 30% of the granite heated up to 250 ℃ and rapidly cooled in 20 ℃ water. The cohesion of granite under thermal shock decreases with the increase of thermal shock cracking, while the internal friction angle increases obviously. The unsteady heat transfer caused by thermal shock has a degrading effect on the mechanical properties of granite. Therefore, the design and construction of drilling engineering and artificial reservoir in hot dry rocks, all requires to consider the influence of thermal shock on the strength.

Key words: granite, thermal shock, mechanical properties, cooling medium temperature, evolution rules