Water inrush hazard seriously threatens construction safety of subsea tunnels in unfavorable geological areas. In recent years, a large number of subsea tunnels have been built worldwide, some of which have experienced many water inrush disasters, especially in Japan and Norway. In this paper, a systematic methodology is proposed to rigorously review the current literature about water inrush in subsea tunnels. Emphasis is placed on recorded causes and evolution processes of water inrush, as well as relevant mitigation measures. In particular, the geological conditions that generate such water inrush hazards are initially discussed by counting cases of tunnel water inrush in the past decades (43 cases of water inrush hazards in tunnels (including mountain tunnels)). The process of formation of failure modes of water inrush, and the corresponding research methods (including theoretical, numerical and experimental) are reviewed, and can be used to pave the ways for hazard prevention and future research. This is followed by a summary of the prevention methods and mitigation measures used in practice, and a short discussion of the achievements and limitations of each method. Then combined with the evolution characteristics of the failure area, the water inrush process of different modes is divided into three stages, with a proposed a grouting scheme for each stage. Finally, concluding remarks, current research gaps and future research directions on subsea tunnel water inrush are provided and discussed.

Because the conventional support system has its own limitations, it is hard to stabilize the surrounding soil which frequently causes the tunnel damage in loess area. Therefore, there has been aroused a great concern for controlling the large deformation during loess tunnel construction. Based on a successful application of the concrete-filled steel tube (CFST) in mining engineering, a novel support type of CFST support system is proposed in this article. The new support system highlights to strengthen the primary lining and to improve the stress distribution between primary and secondary lining. The convergence confinement method and finite element analysis were adopted to investigate the performance of CFST support system and conventional support system, respectively. The results showed that CFST support system presented a better support performance with higher stiffness and greater bearing capacity compared with the conventional support system. In addition, CFST support system effectively decreased the tunnel deformation and extensively increased the safety reserve of secondary lining during the tunneling process. Also, a parametric study was conducted and included investigations on the inner concrete strength, the thickness of the steel tube and the diameter of the CFST. These results help to improve the loess tunnel design and construction.

A method of load calculation in a tunnel was adopted in consideration of the state of covering depth. Due to the macropore characteristics of loess soil, the existing demarcation regulations of deep and shallow tunnels are inappropriate for large-section and shallow loess in highway tunnels. To determine the load of large-section loess tunnel and provide a proper reference for structural design, the theoretical basis for distinguishing depth of deep and shallow tunnels, as well as the characteristics of common calculation methods for surrounding rock load on depth, were analyzed. Through statistical analysis and significance analysis, the significance of the variation of surrounding rock pressure with cover depth was studied. Correlation analysis was carried out on significant results to fit the relationship between cover depth and surrounding rock pressure. The results showed that the surrounding rock pressure varied linearly with the cover depth, and the surrounding rock pressure was about 0.3 times the initial pressure in deep tunnels. The surrounding rock pressure of shallow tunnels did not change significantly with the cover depth, and the surrounding rock pressure was loose pressure. A method based on statistics was proposed to distinguish the cover depth threshold (CDT) of deep and shallow tunnels.

Ensuring the proper operation of tunnel firefighting systems in cold regions is a key issue at hand. According to the characteristics of cold region tunnel fire control systems, this paper puts forward a kind of air heat tracing system (AHTS) that is suitable for cold region tunnel firefighting systems. In the AHTS, an annular air duct was used to heat the firefighting pipe and keep it warm, so that the water temperature in the firefighting pipe is above the freezing point, which helps prevent the water in the firefighting pipe from freezing and avoids the failure of the firefighting system. Meanwhile, the finite element software ANSYS was used to simulate the working state of the AHTS under different conditions, and the insulation effect under different conditions was evaluated. The results showed that the AHTS has a good heating and heat preservation function, which can effectively maintain the normal operation of the tunnel firefighting system in cold regions under a low temperature environment (below 0 °C). Furthermore, increasing the air temperature and air speed in the system was beneficial to the working effect of the AHTS, and the “high temperature and low speed” mode was beneficial to reduce the system power consumption. It is recommended that v = 5 m/s and Ta = 50 °C be used as the preset operating parameters. Finally, according to the numerical analysis results, the scientific and reasonable working parameters of the AHTS under different working conditions were optimized. The research content can provide new ideas and theoretical support for the thermal insulation technology of tunnel firefighting systems in cold regions in the future.

The fractured zone poses a significant risk to construction safety and structure durability in tunnel engineering. However, the effect of excavation methods has not been thoroughly investigated in previous studies. This paper presents a series of 1:30 scale 3D model tests on fault tunnels under the coupling effect of different fault dip angles and construction steps. We measured and analyzed the rock mass deformation and lining structure stress to explore the influence of tunnel excavation by the CD method. The model test results were verified by numerical simulation using the prototype tunnel parameters. Our results show that steeper fault dips correspond to greater radial pressure of the surrounding rock, and pressure in both haunt positions changes more significantly than that in the vault position, while pressure in the side-wall position changes only slightly. Additionally, considerable deformation can be observed in the vault and both haunt positions, with a rock mass relaxation range of less than 1.0 D. For the lining structure stress of each point in the second excavation cycle, larger lining stress is measured in the case of a fault dip of 75° than that in cases when the fault dip equals 45° and 60°, respectively. The biggest stress is observed in the side-wall position after the mid-partition is mantled to form a closed-loop lining structure. Overall, our findings provide valuable insights into the construction response of tunnels through faults and highlight the importance of considering excavation methods in tunnel engineering.