## 3 Test Results
### Changes in Cohesion and Internal Friction Angle  
Cohesion and the internal friction angle are parameters of rock shear strength, where the internal friction angle reflects the friction characteristics of a rock. The main influencing factors include the material, mineral composition, porosity, etc., of the rock, while cohesion is an indicator of the internal bonding strength of a rock and is related to the mineral particle size, bonding composition, and bonding degree. Figure 12 shows the variation trend of the internal friction angle of the rock samples in the different sampling directions with an increasing temperature, as well as the normalized internal friction angle with temperature variation. As shown in Figure 12, the internal friction angle of the rock samples in all three directions showed an overall upwards trend with an increasing temperature, indicating that a high temperature slightly increased the internal friction angle of the granite. Under normal temperature conditions, the internal friction angles of the granite in the three directions were arranged in descending order: Y direction > X direction > Z direction. As the temperature increased to 800 \({}^{\circ}\)C, the internal friction angle of the X-direction rock sample first increased, then decreased, and then increased again, while the internal friction angle of the Y-direction rock sample first slightly decreased. After 400 \({}^{\circ}\)C, the internal friction angle of the Z-direction rock sample increased at a relatively rapid rate, and it approximately linearly increased until it slightly decreased above 600 \({}^{\circ}\)C. When the temperature increased to 1000 \({}^{\circ}\)C, the internal friction angle of the rock samples in the three directions decreased to different degrees, but the values were still greater than those of the original state. Specifically, at 1000 \({}^{\circ}\)C, the feldspar melts formed a smooth glaze surface, resulting in a decrease in the friction coefficient and a decrease in friction between the mineral components. However, due to the high-temperature treatment, a large number of cracks were generated, minerals were broken, and small mineral particles filled the cracks. The friction characteristics of the particles were improved compared to those in the initial state. Therefore, compared with that at 800 \({}^{\circ}\)C, the internal friction angle at 1000 \({}^{\circ}\)C decreased but was still greater than that in the initial state. Figure 13 shows the variation in cohesion with different temperatures in the rock samples from the different sampling directions, as well as the trend in cohesion with an increasing temperature after normalization. Although the cohesion of the rock samples from all three sampling directions decreased overall with an increasing temperature, there were differences in the variation patterns of the different temperature ranges. At 200 \({}^{\circ}\)C, the cohesion of the rock samples in all three sampling directions showed a decreasing trend, but the rate of decrease in the Y direction was significantly lower than that in the other two sampling directions. At 400 \({}^{\circ}\)C, the cohesion of the rock samples in the X direction slightly increased, while the cohesion of the rock samples in the other two directions continued to decrease. The decrease in cohesion of the rock samples in the Z direction was much  
Figure 11: Temperature variation pattern of granite E in different sampling directions. greater in this temperature range than in the other two directions. As the temperature continued to increase, the cohesion of the rock samples in the three directions decreased steadily, and the rates of decrease were relatively close. The effects of temperature on the cohesion of the rock samples in the different sampling directions tended to be consistent. The normalized results reveal that the cohesion of the \(Z\)-direction rock sample was more sensitive to a high-temperature response than was that of the other two directions.