To provide references for the fire prevention design of steel–concrete–steel immersed tube tunnels, four types of test conditions—no fire protection, fireproof coating insulation, single-layer seam fireproof boards, and double-layer seam fireproof boards—were carried out using partial full-size structural test members. Additionally, the thermal insulation effects of various fireproofing technology solutions were contrasted and analyzed. Combined with the numerical simulation analysis, the temperature distribution law inside the tube structure under various fireproofing measures and the temperature rise law of measuring points at different depths were studied, and the protective effect of the fireproof layers on the tube structure under high fire temperature was demonstrated. The results of the numerical simulation and the experimental data agree well. The results show that adding fireproof layers can significantly lower both the steel shell’s surface temperature and the depth of fire impact. Without fire protection, the surface temperature of the bottom steel shell exceeds 300 °C at 69 s, and the member bursts. The fireproof coatings are cracked and flaking and cannot meet the fire resistance limits. Both single-seam and double-seam schemes of calcium silicate boards can meet the fire resistance limit requirements and the latter has a better heat insulation effect.

A new type of steel–concrete–steel composite structure was adopted and widely used in the immersed tunnel of the Shenzhen–Zhongshan access. The research on the mechanical behavior of the new composite structure under a high temperature of fire is of great engineering significance to the fire protection design of the structure. Both the model test and a numerical simulation were adopted to study the mechanical behavior and damage characteristics of the new composite structure under fire. The RABT standard temperature rise curve was used to simulate the temperature rising law under fire (it reflects the characteristics of temperature rise in case of fire in an enclosed environment: rapidly raised to 1200 °C within 5 min, maintained at 1200 °C for 120 min, then it is cooled to normal temperature after 110 min). The temperature distribution law inside the structure, the deformation development law of the roof and the crack distribution were analyzed based on the thermal–mechanical coupling analysis method. The results showed that the internal part of the composite structure close to the fire surface was directly affected by the high temperature, and the temperature presented a step distribution law, while the part far from the fire surface was affected by the lag effect of the temperature transfer, and the temperature presented a continuous growth law. The roof deformation presented a three-stage model of “rapid growth-deformation stability-deformation recovery” with time. The overall cracks of the composite structure showed a symmetrical distribution under fire. The composite structure presented a shear failure mode as a whole. The results could provide a reference for the study of fire resistance for the new composite structure and support the structural fire protection design of the immersed tunnel of the Shenzhen–Zhongshan access.

Taking the Jiangluling Carbonaceous Shale Tunnel as an example, this study aims to investigate the mechanism of large deformation and design construction technology of carbonaceous shale tunnels. Using theoretical analysis and comparative analysis of numerical simulation and field measured data, the mechanism, mechanical properties, and causes of large squeezing deformation of the Jiangluling Tunnel were analyzed. The study results are as follows: 1) Six failure modes of the support structure can be generated due to the large deformation of the surrounding rocks during the construction of Jiangluling Carbonaceous Shale Tunnel; 2) The causes of large deformation during the construction can be divided into internal and external causes; 3) The deformation degree of the surrounding rock of Jiangluling Carbonaceous Shale Tunnel increases with the burial depth in an approximately linear manner. Under deep-buried conditions, horizontal convergence is more severe than vault settlement in carbonaceous shale tunnels; 4) The deformation of the construction cavern of the Jiangluling Carbonaceous Shale Tunnel typically includes the displacement before tunnel face excavation, tunnel face deformation, and deformation behind the tunnel face. The advance displacement accounts for 30.73% of the total displacement. The influence range of advance displacement is 1-1.2D in front of the tunnel face. These results can provide a reference for the design and construction of carbonaceous shale tunnels.

Aiming at the unclear bearing mechanism of the single-layer lining structure of high-performance fiber shotcrete under layered construction in the hard rock section of a highway tunnel, this paper studies the effect of different thickness ratios under layered construction on the flexural performance of the single-layer lining structure. Six types of thickness ratio specimens were subjected to a four-point bending test. The tests employed 3D digital image correlation technology to record and analyze the deformation and failure process of the specimens, and the calculation method of single-layer lining flexural stiffness was modified. The results indicate that the flexural ultimate load of the specimens is achieved at a thickness ratio of 2, which is 20.9% higher compared to a thickness ratio of 0. Layered construction affects the failure mode of the specimens. All specimens exhibit mixed-mode failure. However, with the increase in the thickness ratio, the percentage of flexural failure cracks gradually increases. Under layered construction, the reduction in the effective bending stiffness of fiber shotcrete beams becomes more pronounced as the thickness ratio increases. Based on these findings, the interface influence factor is proposed, and the flexural stiffness is corrected using composite beam theory.

The construction of transportation infrastructure is transferring from ground to underground, which could evacuate the urban traffic and is also the future trend of the expansion of our cities. The cobble stratum brings about many technical problems in the underground engineering. Based on the calibration test and macroscopic mechanical characteristic curve, the microscopic calculation parameters of particle flow code simulation used for cobble strata in Urumchi were determined. According to establishing the numerical model of pebble tunnels using double-side-drift method, both the ground deformation and force chain evolution were analyzed for the tunnels using subsurface excavation method. This manuscript presented the differentiation of influence on ground deformation in cobble stratum under different excavation stages, the influence extent was ranked as follows, upper bench > double-side-drift > lower bench; the result of numerical simulation test was compared with the field monitoring data, proving that it is reasonable to adopt the particle flow code to simulate the excavation of pebble tunnels, and the research result could be provided for reference for the similar engineering.