As one of the main thermal storage medium of hot dry rock geothermal resources, granite is often subject to frequent thermal shock during the geothermal exploitation. Grasping the response regularity of granite to thermal shock is of great significance to the construction and long-term reliability evaluation of enhanced geothermal system (EGS). This paper investigated the physical and mechanical properties of granite after 0∼20 thermal shocks, and discussed its internal deterioration mechanism. Combined with ANSYS numerical simulation analysis, the mechanical formation mechanism of thermal cracks that lead to the deterioration of physical and mechanical properties of granite was analyzed. The results show that the first thermal shock tends to cause the severest deterioration to both physical and mechanical properties of granite. But when the number of thermal shocks exceeds 10, the deterioration slows down. The increase in contact thermal resistance between mineral particles after cyclic thermal shock results in a decrease in the thermal conductivity of granite. The enhancement of local stress concentration effect and the increase of local bearing capacity difference of granite after cyclic thermal shock result in the decrease of peak strength and the enhancement of ductility characteristics of granite. Due to the existence of thermal cracks, the granite after cyclic thermal shock has one more path to release the energy stored during the loading process than the natural granite. Therefore, the maximum counts at the beginning of crack propagation and the entire crack propagation stage are smaller than that of the natural granite. During the thermal shock, the huge instantaneous temperature difference between the interior and exterior of granite leads to the formation of thermal stress, which increases rapidly and then disappears gradually. As a result, the interior of granite mainly bears the effect of the vertical compressive thermal stress up to 7.59 MPa, while the exterior of granite mainly bears the effect of vertical tensile thermal stress up to 9.18 MPa. The propagation of some pre-existing micro cracks with proper orientation in the interior of granite and the initiation and propagation of secondary thermal cracks on granite surface are identified as two main causes to the deterioration of the physical and mechanical properties of granite after cyclic thermal shock.

花岗岩作为干热岩地热资源的主要蓄热介质之一，在地热开发过程中经常受到频繁的热冲击。掌握花岗岩对热冲击的响应规律对于增强型地热系统（EGS）的建设和长期可靠性评价具有重要意义。本文研究了花岗岩在0～20次热冲击后的物理力学性能，并讨论了其内部劣化机制。结合ANSYS数值模拟分析，分析了导致花岗岩物理力学性能恶化的热裂纹的力学形成机制。结果表明，第一次热冲击往往对花岗岩的物理和机械性能造成最严重的恶化。但当热冲击次数超过 10 次时，恶化速度会减慢。循环热冲击后矿物颗粒之间接触热阻的增加导致花岗岩的导热系数降低。循环热冲击后花岗岩局部应力集中效应的增强和局部承载力差异的增大导致花岗岩峰值强度的降低和延性特性的增强。由于热裂纹的存在，循环热冲击后的花岗岩比天然花岗岩多了一条释放加载过程中储存的能量的途径。因此，裂纹扩展开始和整个裂纹扩展阶段的最大计数小于天然花岗岩。在热冲击期间，花岗岩内外瞬间巨大的温差导致热应力的形成，热应力迅速增大后逐渐消失。因此，花岗岩的内部主要承受高达7.59 MPa的竖向压热应力的影响，而花岗岩的外部主要承受高达9.18 MPa的竖向拉热应力的影响。花岗岩内部一些具有适当取向的先存微裂纹的扩展和花岗岩表面二次热裂纹的萌生和扩展被认为是循环热冲击后花岗岩物理力学性能恶化的两个主要原因。 . 它迅速增加然后逐渐消失。因此，花岗岩的内部主要承受高达7.59 MPa的竖向压热应力的影响，而花岗岩的外部主要承受高达9.18 MPa的竖向拉热应力的影响。花岗岩内部一些具有适当取向的先存微裂纹的扩展和花岗岩表面二次热裂纹的萌生和扩展被认为是循环热冲击后花岗岩物理力学性能恶化的两个主要原因。 . 它迅速增加然后逐渐消失。因此，花岗岩的内部主要承受高达7.59 MPa的竖向压热应力的影响，而花岗岩的外部主要承受高达9.18 MPa的竖向拉热应力的影响。花岗岩内部一些具有适当取向的先存微裂纹的扩展和花岗岩表面二次热裂纹的萌生和扩展被认为是循环热冲击后花岗岩物理力学性能恶化的两个主要原因。 . 18兆帕。花岗岩内部一些具有适当取向的先存微裂纹的扩展和花岗岩表面二次热裂纹的萌生和扩展被认为是循环热冲击后花岗岩物理力学性能恶化的两个主要原因。 . 18兆帕。花岗岩内部一些具有适当取向的先存微裂纹的扩展和花岗岩表面二次热裂纹的萌生和扩展被认为是循环热冲击后花岗岩物理力学性能恶化的两个主要原因。 .