Deep buried tunnel has a complex stress environment and large stress level. At present, it is difficult to dynamic monitoring for such tunnels. In order to make the safety evaluation and prediction of tunnel closer to the engineering practice, this paper deduces the tunnel reliability evaluation algorithm. The time-varying reliability of deep tunnel excavation process is analyzed and predicted. Based on the similarity theory, the actual deep tunnel excavation is simulated by indoor model test, the stress and deformation are monitored. The results show that after the tunnel excavation, the reliability of the structure does not decrease gradually, but increases slowly first and then decreases sharply. With the increase of the buried depth of the tunnel, the structural reliability decreases gradually. When the buried depth reaches a certain depth, the structural reliability will decrease rapidly. The influence of different parameters on the structural reliability has different sensitivity. The sensitivity of friction angle is the highest, and the sensitivity of gravity is the lowest. The sensitivity has little effect with the change of tunnel excavation time and tunnel buried depth. The accuracy of this method is verified by the comparative analysis of model box tests.

It is difficult to monitor the deformation of a rock mass in front of a tunnel owing to the large buried depth and complex geological conditions. In this study, by using a self-designed model test box as a carrier and using loess, sand, gypsum, cement, and water as the raw materials, the class V materials similar to the surrounding rock are obtained through an orthogonal test. These are used to study the deformation law of a rock mass in front of a tunnel in different ground stress soft rock. The results show that similar materials for the surrounding rock can meet the needs of the testing concerning the physical and mechanical properties and have economic and environmental protection advantages. The three-dimensional loading of a similar geological body is used to simulate the state of the rock mass. The real-time monitoring of the rock mass stress and deformation is conducted during a simulation of tunnel excavation, and the deformation laws of the rock mass and surrounding rock in front of the tunnel are obtained. In the range of 0.26 times the tunnel diameter in front of the tunnel in the high ground stress soft rock, the deformation of the core rock mass is the largest part of the tunnel deformation. Therefore, to reasonably control the advanced deformation of the tunnel, it is necessary to pre-reinforce the core rock mass within 0.26 times the tunnel diameter in front of the tunnel. At 1 times the diameter in front of the face, a longitudinal load-bearing arch is formed in the rock mass, and this effectively controls the extrusion deformation of the core rock mass to expand forward.

In order to ensure that no freezing damage occurs during the service period of the tunnels in the cold areas, the tunnel temperature field model test bench is built according to the similarity principle to study the change rule of the temperature inside the tunnels in the cold season, and a new type of active thermal insulation technology is proposed - air curtain thermal insulation technology at the tunnel portal. Using the principle of superposition of stream function and heat balance, the control equation of air curtain thermal insulation technology is derived, using the principle of superposition and Bessel differential equation to derive the theoretical solution of the radial temperature of the surrounding rock at the tunnel portal section in the cold area under the air curtain action, and finally the feasibility of the insulation technology is verified by taking the Zhengpantai Tunnel as an example. The conclusions of the study show that: the outside ambient temperature and the surrounding rock temperature are the main factors affecting the temperature field of the tunnels in the cold areas; The finite element calculation result shows that the air curtain insulation technology can effectively prevent tunnel freezing damage; there is little difference between the theoretical solution of tunnel radial temperature and the finite element calculation result, and the theoretical solution can provide a theoretical basis for the future practice of the project; the property of the air curtain jet is analyzed, and the air curtain thermal insulation technology can be summarized as heating is primary and air isolation is secondary.

Mudstone is highly sensitive to water. When it comes into contact with water, the softening phenomena such as the decrease of strength and the increase of deformation are prominent. It is of great significance to clarify its related mechanical properties. For the tertiary mudstone, a triaxial compression test and a Brazilian splitting test are carried out under the conditions of four kinds of water content (0, 10.1%, 12.5%, and 14.1%) and four kinds of confining pressures (0 MPa, 2 MPa, 5 Mpa, and 10 MPa). The test results show that (1) with the increase of confining pressure and water content, the mudstone changes from brittle failure to ductile failure. The higher the confining pressure, the greater the strength and elastic modulus. The higher the water content, the significantly lower the strength and elastic modulus, and the higher the strain. (2) With the increase of water content, the influence of confining pressure on strength is more prominent. High confining pressure can effectively inhibit the trend of strength attenuation. (3) When the water content is low (0–10.1%), the strength of the mudstone is mainly related to its own water content. When the water content increases to 10.1%–14.1%, both the confining pressure and the water content are important factors affecting the strength of the mudstone. Then, the applicability of five commonly used strength criteria to the strength prediction of softened mudstone is compared and analyzed. The results show that the Rocker strength criterion can more accurately and conveniently predict the strength of mudstone under different water content. Finally, based on this strength criterion, a nonlinear strength prediction model of softened mudstone considering water content and confining pressure effect is proposed and its good applicability is verified.

Suspension bridge is a flexible structure. The weight, location and number of traffic on the bridge will affect the geometric alignment of the bridge. Although the finite element software can analyze the geometric nonlinearity of the bridge, the calculation of random load combination in finite element software is huge. In this paper, based on the deformation coordination, static equilibrium and constitutive model of the bridge, the force expression considering the geometric nonlinearity of the bridge is derived. Finite element software is used to simulate the internal force of components of suspension bridge under train load and vehicle load. The accuracy is verified by comparing the finite element results. Considering the random number of traffics, the random location of traffics, and the random weight of traffics, this paper analyzes the stress state of bridge under the random process of train load and vehicle load respectively. The method in this paper can be well used to analyze the actual stress state of the bridge, and provide a theoretical basis for related calculations.