# Study on Damage Behavior and Its Energy Distribution of Deep Granite at High-Temperature Conditions
## 3 Acoustic Emission Test Results and Analysis of Fractured Rock under Triaxial Loading  
### Total Stress-Strain Curve and Failure Mode  
Figure 3 shows the stress-strain curves of samples with different initial thermal damage under conventional triaxial compression under three different confining pressures. The results show that the samples with different initial thermal damage under different confining pressures all underwent fracture compaction, elastic, fracture development and strain softening stages. With the increase in confining pressure, the cracks in the sample are compressed to different degrees. The closer the equivalent damage factors are, the less obvious the compaction stage is on the stress-strain curve. In the fracture development stage, the internal fractures of rock are fully developed before the peak due to confining pressure; therefore, the greater the peak front wall pressure, the more obvious the softening effect. In the post-peak failure stage, the greater the confining pressure, the stress drop rate gradually changes from fast to slow. Figure 2: Relationship between granite porosity and p-wave velocity with temperature: (**a**) the porosity variation of samples treated at different temperatures; (**b**) variation of longitudinal p-wave velocity of samples. In order to quantitatively describe the influence of confining pressure and crack on the specimen compression deformation failure process, the characteristic mechanical parameters in Figure 3 were extracted, and the changes in characteristic mechanical parameters of rock with crack were plotted under different confining pressures, as shown in Figure 4. As can be seen from Figure 4a,b, the peak stress and its corresponding strain increase with the increase in confining pressure for rock samples with similar equivalent damage factors; however, when the confining pressure is the same, the greater the confining pressure, the difference in peak stress of different initial thermally damaged samples becomes smaller and smaller, and the peak stress of samples is almost the same under the confining pressure of 10 MPa and 20 MPa. However, the difference of peak strain of samples with different initial thermal damage under the same confining pressure does not decrease with the increase in confining pressure, indicating that the peak stress of samples is sensitive to confining pressure, and the peak strain is sensitive to the effect of equivalent fracture damage factor. Meanwhile, Figure 4c shows that the greater the confining pressure, the smaller the elastic modulus, and the smaller the equivalent damage factor under the same confining pressure, the greater the elastic modulus; however, for the sample with D = 0.89, the elastic modulus does not change significantly with the increase in confining pressure because the internal cracks are relatively developed. Figure 3: Stress–strain curves under different confining pressures: (**a**) D = 0.16; (**b**) D = 0.36; (**c**) D = 0.51; and (**d**) D = 0.89. Failure patterns of rocks under different confining pressures are shown in Table 1. As can be seen from the table, for rocks with similar equivalent damage factors, with the increase in confining pressure, the failure mode of specimens gradually transitions from axial splitting failure to macroscopic splitting surface with a certain angle to axial direction. In addition, under a low confining pressure, the more cracks in the sample are developed, the more sub-splitting surfaces are formed during the failure of the sample. For example, under 0 MPa, the equivalent damage factors in the cracks have the most obvious influence on the failure mode of rock. However, with the increase in confining pressure, the effect of equivalent damage factors in rock mass on the failure mode decreases.