## 1 Introduction  
In nuclear waste disposal, geothermal energy development and so on, rock mechanics' problems often occur after high temperature. The related parameters of rock after high temperature are the main basis for engineering stability analysis and design. At present, many scholars have carried out relevant research on the mechanical behavior of rock after high temperature. High temperature causes thermal expansion, thermal reaction and thermal stress of minerals inside the rock, which all lead to cracks inside the mineral and changes in the rock microstructure, further to changes in the rock-related properties [1, 2]. With the increase in temperature, the mass of the rock decreases gradually and this is mainly related to the change of water occurrence inside the rock. During the heating process, the bound water, crystal water and mineral water inside the rock gradually precipitate with the increase of temperature [3, 4]. [PERSON] et al. [5] found that in the case of temperature rise, the volume and specific heat capacity of granite, which had withstood high temperatures,increased. The longitudinal wave velocity, mass, density, thermal conductivity and thermal diffusion coefficient of it decreased. Through thin section observation, it was found that there were no obvious thermal cracks in the rock samples after different temperature treatments, but many thermal cracks appeared between the particle cements [6]. At 500-600 \({}^{\circ}\)C, the linear expansion coefficient of quartz increased rapidly in both vertical and parallel to the c axis direction, which was mainly due to the \(\alpha\)-\(\beta\) phase transition of quartz at about 573 \({}^{\circ}\)C, and that the volume of quartz increased by 2.4% [7; 8]. The related mechanical properties of granite treated by different high temperatures were studied and it was found that 400 \({}^{\circ}\)C was a threshold value for performance change [9]. Through the uniaxial compression test of granite after high temperature treatment, [PERSON] et al. [10] had studied the influence of temperature on the crack damage, strength and deformation failure behavior of granite. [PERSON] et al. [11] had found that the physical and mechanical properties of granite deteriorated significantly after heat treatment. Through the experimental study of granite under different high temperatures, [PERSON] et al. [12] found that the strength and deformation characteristics of granite samples gradually became stronger, with the increase of confining pressure. A series of studies were carried out on the physical and mechanical properties of high temperature rock. Most of the scholars have studied the natural cooling of high temperature rock, but that often involves the rapid cooling of water in practical projects, such as geothermal energy mining. Therefore, some scholars have carried out relevant studies to conduct natural cooling and water cooling treatments on granite. When the heat treatment temperature is 25-200 \({}^{\circ}\)C, the cooling method has little effect on the physical properties and the wave velocity of different granite samples. With the increasing temperature, the parameter attenuation gradually intensifies, and the water cooling method has a greater effect [13]. [PERSON] et al. [14] found that, with the increase of temperature, the wave velocity, elastic modulus and linear of granite after natural cooling decreased. [PERSON] et al. [15] studied the meso-damage of granite under different cooling methods. Combined with SEM study, it was found that, with the increase of temperature, the damage to the granite was more serious. The thermal damage of granite is the combined influence of the mechanism of mineral particle expansion and shrinkage, cold shock and thermal physical and chemical changes. [PERSON] et al. [16] studied the tensile strength of granite by different cooling methods. They found that the tensile strength of granite decreases and the rock fracture surface changes to rough and tortuous with the increase in temperature.