Tunnel construction sites pose a significant safety risk to workers due to the low-light conditions that can affect visibility and lead to accidents. Therefore, identifying personal protective equipment (PPE) is critical to prevent injuries and fatalities. A few researches have addressed the challenges posed by tunnel construction sites whose light conditions are lower and images are captured from a distance. In this study, we proposed an improved YOLOX approach and a new dataset for detecting low-light and small PPE. We modified the YOLOX architecture by adding ConvNeXt modules to the backbone for deep feature extraction and introducing the fourth YOLOX head for enhancing multiscale prediction. Additionally, we adopted the CLAHE algorithm for augmenting low-light images after comparing it with eight other methods. Consequently, the improved YOLOX approach achieves a mean average precision of 86.94%, which is 4.23% higher than the original model and outperforms selected state-of-the-art. It also improves the average precision of small object classes by 7.17% on average and attains a real-time processing speed of 22 FPS (Frames Per Second). Furthermore, we constructed a novel dataset with 8285 low-light instances and 6814 small ones. The improved YOLOX approach offers accurate and efficient detection performance, which can reduce safety incidents on tunnel construction sites.

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.

In waterproofing mountain tunnels, the tunnel joint is the weak link. To explore the waterproof failure mechanism of the tunnel joint waterstop belt and to propose an optimization method for the waterstop belt, this paper combines tests and numerical simulations, summarizes the waterproofing mechanism of the waterstop belt, establishes a finite element model of the waterstop belt considering bonding and extrusion, and studies the waterproofing ability and mechanical properties of the waterstop. The main conclusions are as follows: (1) The waterproofing capacity of the water stop belt depends on its surface contact pressure and bonding force. (2) Waterstop deformation will partially destroy the bonding between the waterstop and concrete, reducing the reliability of the waterproofing mechanism. (3) When the deformation of the waterstop belt reaches a certain degree, its stress value is too large to meet the requirements of its service life. (4) The design can be optimized from two aspects: the bond between the waterstop and concrete, and the size of the waterstop.

Loess tunnels often undergo large-scale deformation with complex spatial and temporal distribution. Mastering the characteristics of spatial and temporal deformation is conducive to precise policy implementation and the control of large deformation of the tunnel. In this study, relying on the Yulinzi Tunnel in Gansu Province, China, based on 3D laser scanning technology, the tunnel was monitored for a short period of 24 h and a long period of 36 days. The refined characteristics of the temporal and spatial deformation of the representative points of the interrupted surface, the tunnel face, and the excavation mileage during the excavation process of the three-bench and seven-step method of the tunnel were analyzed. The results show that the tunnel’s arch has large deformation, and there is twisting deformation. The distribution of the overall deformation of the tunnel is related to the excavation sequence, showing a stepped deformation law. With the construction of the following excavation process, the deformation rate of the tunnel always indicates the characteristics of significant in the early stage and small in the later stage, and the overall deformation changes with time in accordance with the distribution law of the exponential function. The research results provide a reference for predicting the deformation development trend of loess tunnels and providing reasonable deformation control methods.

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.