## 4 Discussion  
Different cooling modes of high temperature rock mass are complex processes, and natural cooling and water cooling have different effects on rock mass. Under the action of high temperatures, the rock structure, mineral composition and grain cementation will change [6], affecting the related properties of the rock. During the high temperature treatment of rock, due to the different mineral composition and thermal expansion coefficient of granite, thermal stress is generated between the internal particles of granite, resulting in different types of thermal cracks in the high temperature rock mass. For high-temperature rocks under natural cooling, the high temperature causes plastic deformation of the internal  
Figure 11: Failure modes of granite with different cooling modes. (**a**) Failure modes of granite under natural cooling; (**b**) Failure modes of granite under cooling in water.  
particles of the rock, and the internal minerals shrink and deform in an uncoordinated manner, filling the gaps between some of the particles. On the other hand, for the high-temperature rock cooled by water, the sample is rapidly cooled, and more thermal cracks are generated in the internal particles. The process is shown in Figure 12.  
Furthermore, the cooling temperature of the sample under the action of natural cooling and water cooling presents a gradient change, and the outer part of the high temperature rock cools first, and then the inner part gradually cools. In this process, due to the change of the temperature gradient, the temperature difference between the inside and outside of the sample is generated, thermal stress is generated between the particles, and with the increase in thermal stress, more thermal cracks appear inside the sample. Because the high-temperature rock cools faster under the action of water cooling [20], the temperature gradient of the sample after being cooled by water is more obvious, which is the reason for more cracks in the water-cooled sample. The sample-related properties are worse than those of the naturally cooled sample, and the gradient changes are shown in Figure 12.  
After different cooling methods, the strength of the sample increases before 400 \({}^{\circ}\)C, and decreases after 400 \({}^{\circ}\)C. Therefore, reducing the temperature when the actual engineering temperature is above 400 \({}^{\circ}\)C is beneficial to the safety of the actual engineering. The change of the mechanical properties of the sample under the action of natural cooling is better than that of the sample under water cooling. It can be seen from the failure mode of the sample that the natural cooling sample is looser. Therefore, it is necessary to select an appropriate method for construction in real-life engineering.  
This paper only considers the mechanical properties and fracture characteristics of the sample with a single cooling cycle in water. It does not the effect of multiple cooling cycles in water on the sample, nor does it consider the effect of dynamic loads in actual engineering. We will continue to carry out related research in future work, and the research results of this paper provide certain reference value for future related research.  
Figure 12: Damage process of granite sample under different cooling modes.