## 3 Test Results
### Changes in Longitudinal and Transverse Wave Velocities  
The effects of temperature on the longitudinal and transverse wave velocities of granite are shown in Figures 8 and 9, respectively. At temperatures ranging from 200 to 400 \({}^{\circ}\)C, the longitudinal wave velocity approximately linearly decreased, and the rate of decrease in the longitudinal wave velocity was significantly greater than that in the transverse wave velocity. At 400 \({}^{\circ}\)C, the longitudinal wave velocity of granite decreased to 2738 m/s, which was only 61% of that at room temperature. Although the transverse wave velocity decreased with an increasing temperature, it could still reach 76% of that at 400 \({}^{\circ}\)C. At 600 \({}^{\circ}\)C, the longitudinal wave velocity continued to decrease rapidly, with the average  
Figure 7: Crack photographs of granite sample slices after different temperature treatments. longitudinal wave velocity dropping to 1312 m/s, which was only 29% of that at room temperature. The transverse wave velocity decreased significantly faster than that at 400 \({}^{\circ}\)C, dropping to 42% at room temperature. As the temperature continued to increase, the rate of decrease in the wave velocity slowed. At 800 \({}^{\circ}\)C, the longitudinal wave velocity decreased to 1009 m/s, and the transverse wave velocity decreased to 846 m/s. When the heating temperature reached 1000 \({}^{\circ}\)C, the ultrasonic signal became extremely chaotic and unstable, and the wave velocity could not be read anymore. There was a significant change in the wave velocity of the granite before and after 400 \({}^{\circ}\)C, and 400 \({}^{\circ}\)C can be regarded as the threshold temperature for thermal damage to the granite wave velocity. The law of the variation in wave velocity with different temperatures in the three orthogonal directions of granite can be summarized as follows: at room temperature, the Z-direction wave velocity was the highest, and the Y-direction wave velocity was the lowest. As the heating temperature increased, the longitudinal wave velocity of granite, in the first three sampling directions before 400 \({}^{\circ}\)C, decreased rapidly, and the Z direction had a faster deceleration rate, while the X direction and Y directions had a slower deceleration rate. The difference in the longitudinal wave velocity of granite in the three directions decreased rapidly, and the difference in the longitudinal wave velocity was the smallest at 400 \({}^{\circ}\)C. For the shear wave velocity, at 200 \({}^{\circ}\)C, the reduction rate of granite in the three  
Figure 8: Temperature-dependent variation in the longitudinal wave velocity of granite in different sampling directions. Figure 9: Variation in transverse wave velocity of granite with different temperatures in different sampling directions. directions was basically the same and still significantly different. At 400 \({}^{\circ}\)C, the reduction rate of the granite shear wave velocity in the X direction was significantly greater than that in the other two directions, rapidly decreasing to the same level as the shear wave velocity in the Y direction. When the temperature exceeded 400 \({}^{\circ}\)C, the variation patterns of the longitudinal and transverse wave velocities of granite in the three directions were basically the same. The wave velocities of granite in the X and Y directions tended to be consistent and significantly lower than those of granite in the Z direction. When the heating temperature reached 800 \({}^{\circ}\)C, the relationship between the longitudinal wave velocities of granite in the three directions was the same as that for normal temperatures, but the difference was not significant, while the transverse wave velocities of granite in the Z direction were still significantly greater than those in the other two directions. In summary, there was a significant difference in the influence of temperature on the longitudinal and transverse wave velocities of granite.