## 3 Research Progress of High-Temperature Rock Mechanics in Large-Buried Tunnels
### Rheological Mechanism and Control Technology of Surrounding Rocks  
Considering thermal behavior, [PERSON] et al. [76] proposed a detailed scheme for tunnel by simulation method, which is a powerful tool to execute relevant research in the field of geotechnical engineering [77; 78; 79]. Figure 1 is the completed model with the heat transfer boundary conditions of a half tunnel, and a detailed cross-section is presented in Figure 2. Specifically, the length of the modeled second lining block is 12.2 m, and the thickness is 0.3 m. The thicknesses of the invert, rock layer, and shotcrete are 0.45 m, 2 m, and 0.15 m, respectively. The length of the previously corrected lining is 6.1 m.  
[PERSON] and [PERSON] [80] used elastic theory to analyze the thermal stress at the openings of lined and unlined cylindrical and spherical underground caverns, and pointed out that the support pressure and lining stress only depend on the temperature distribution inside the lining. [PERSON] [81] obtained a rheological model reflecting the rheological properties of gneiss by laboratory triaxial compression rheological tests at different temperatures, and analyzed the relationship between the parameters of the rheological model and temperature. Through the triaxial tests of granite under the conditions of high temperature and high pressure, [PERSON] et al. [82] and [PERSON] et al. [83] found that there were obvious critical values of stress and temperature in the rheological process of granite, which was about 300-400 \({}^{\circ}\)C. If the threshold is exceeded, the rock shows obvious accelerated creep characteristics.  
The surrounding rock often exhibits creep characteristics [84; 85], it has influence on supporting structure [86], scholars often use theoretical and numerical simulation methods to carry out research [87; 88]. [PERSON] [89] used numerical simulation method to study the high-geotemperature problems existing in the Lari railway tunnel. The size and displacement of the plastic zone, as well as the stress of support structure, around the tunnel at different stages of construction were analyzed, and the critical temperature at which the initial support fails, the development law of the secondary lining and the critical temperature of failure were determined. [PERSON] [90] obtained the calculation formula of mechanical properties of concrete materials for primary support and secondary lining under variable temperature curing conditions through laboratory tests. Besides, the stress characteristics of support structure under different initial temperature of surrounding rock were obtained through thermal-mechanical coupling calculation, and the reasonable support structure for high-temperature tunnel was proposed. Against the background of the tunnel in the high geothermal and deep buried environment, [PERSON] et al. [91] discussed the influence of the thermal insulation layer on the tunnel support structure by combining indoor tests with numerical analysis, and found that the thermal insulation layer has a significant role in optimizing the stress of the secondary lining. [PERSON] et al. [92] studied the mechanical characteristics of reinforced concrete secondary lining of Grade IV and Grade V surrounding rock under different ground temperatures by means of numerical simulation with finite element software. The results indicated that with the increase of geotemperature, the safety factor of the secondary lining shows a downward trend, and it decreases significantly when the local temperature rises from 30 to 50 \({}^{\circ}\)C.