The linings of tunnels in cold regions with long service lives usually have cracks, with parts of the structure peeling and falling off, which seriously threatens the tunnel safety and operation. The unsaturated freeze–thaw cycle of concrete, which is the main cause of structural deterioration, has not received much research attention. During the service life of tunnels in cold regions, unsaturated freeze–thaw cycles deteriorate the quality of the concrete, and its degree presents a gradual distribution in the circumferential and longitudinal directions. An experiment system was adopted to simulate the distribution of the progressive deterioration of tunnel lining concrete. The test results of the temperature field of the model show the distribution law of freeze–thaw cycles, and the gradual deterioration of the lining concrete was realized. Then, the bearing capacity of the model was tested after the progressive deterioration. The results show that the ultimate load of the model decreases with an increase in the number of freeze–thaw cycles. Finally, a numerical simulation was carried out to discuss the influence of the gradual deterioration of the lining. The gradual deterioration of lining concrete will encourage the gradual development of cracks, leading to serious cracking of the lining structure and even block spalling. Through this study, we hope to provide useful information for the prevention and control of tunnel frost damage in cold regions.

Feet-lock steel pipes have been widely applied in soft-rock tunnels, but their installation quantity and parameters depend on engineering experience. In this study, by simplifying the force between the feet-lock steel pipe and the primary lining, the load-deformation characteristics were analyzed separately, and inconsistent deformation was revealed. Next, combined with the passive and active bearing scheme, a design optimization method for feet-lock steel pipes was proposed under two working conditions, including the predicted large deformation and observed large deformation before the primary lining construction. Finally, the design method was applied to the Yulinzi Tunnel, and the results show that the original design of the feet-lock steel pipes could not meet the requirements of the controlling settlement. After the optimized design, both the passive bearing scheme installing two ϕ108 × 3-millimeter steel pipes and the active bearing scheme installing one ϕ108 × 4-millimeter steel pipe could meet the requirements of the controlling settlement. The active bearing design can significantly reduce the amount of steel required and the engineering cost. The scientificity and feasibility of the design optimization method were proven by the on-site monitoring and measurement.

The excavation of a foundation pit will cause soil unloading, resulting in the structural deformation of underlying tunnels, which affects the safety of tunnel operation. Here, the impact of foundation pit excavation on the structural deformation of the metro interval tunnel underlying a foundation pit support project for a storage pond is analyzed through theoretical analysis, numerical simulation, and on-site monitoring, and corresponding safety control measures are proposed. The research shows that simplifying the tunnel into an infinite-length Euler–Bernoulli beam resting on the Kerr foundation model has good rationality and applicability when analyzing the impact of pit construction on the deformation of the interval tunnel. The distance between the foundation pit and the tunnel cross-section significantly affects the deformation of the tunnel structure, and the shorter the straight-line distance from the pit foundation, the more obvious the structural deformation of the interval tunnel. The maximum deformation of the tunnel structure occurs in the upper-left area of the middle of the tunnel near the foundation pit, and the deformation shows a nonlinear decreasing trend toward the two ends of the tunnel. Timely support can effectively inhibit the deformation of the foundation pit, and the spatial and temporal effects of foundation pit excavation on the underlying tunnels should be minimized during construction. The impact on the structural deformation of the underlying tunnels should be mitigated in strict accordance with the three-level control principle: early warning, alarm, and control. The research results provide a reference for guiding foundation pit construction.

The Bohai Strait Channel (BSC) is a strategic infrastructure project connecting the Shandong Peninsula and northeastern China. One challenge related to building the BSC tunnel portion is that ventilation shafts cannot be constructed due to certain limitations, which leads to a barrier for ventilation design. To explore the feasibility of ventilation without shafts, we first compare the tunnel ventilation design methods in China and the European Union. We also present the development process of emission standards, base emission rates, and design concentration values. Then, a new ventilation calculation for the BSC tunnel with reference values from the World Road Association (PIARC) is presented. The results show that the longitudinal ventilation design without shafts is feasible under normal traffic conditions when adopting values designed by PIARC under both the Chinese method and the European method. Furthermore, the influence of new energy vehicles and the necessity of ventilation rate on ventilation design are discussed. We suggest considering new energy vehicle fire situations and ignoring the ventilation rate for BSC tunnels. We hope to provide a strong reference for the ventilation design of BSC tunnels and for the improvement of relative ventilation codes in China.

The prediction and early warning of tunnel collapse in weak surrounding rock is very important for tunnel construction safety, but the current monitoring methods are insufficient. In view of the shortcomings of existing monitoring methods for deformation of advanced core soil, a monitoring method of pre-convergence deformation of advanced core soil in front of the tunnel face was proposed; this involves placing an array displacement meter (ADME) in a leading small conduit and monitoring the deformation of the leading small conduit. The coupling accuracy test data of the ADME and steel pipe were combined to prove the feasibility of the device and test method. Finally, it is proposed to place the ADME in the lead duct, calculate the displacement of the measuring unit through the change of gravity and angle, and obtain the pre-convergence deformation of the lead core soil in front of the palm face. The results show that the floating error of the measuring unit of the ADME is 0.2 mm by calibrating the precision measuring device designed by itself. The absolute error is 0.2 mm @ 1 m. When the ADME is used for deformation measurement with displacement greater than 2 mm @ 1 m, the relative error can be controlled within 10%. Through the above deformation monitoring system, it is expected to realize a real-time monitoring method which can ensure monitoring accuracy and frequency, reduce interference to tunnel construction, and improve the safety and accuracy of tunnel construction in weak surrounding rock.