To address the challenge of structural deterioration caused by frequent cracking in the lining structures of deep-buried hydraulic tunnels in high-altitude areas, the enhancement of concrete's mechanical properties is investigated through the addition of fibers and determines the optimal fiber content for practical engineering application. Firstly, tests on the tensile, compressive, and flexural mechanical properties of basalt fiber-reinforced concrete (BFRC) with varying fiber contents were conducted, the variation patterns of concrete's tensile, compressive, and flexural mechanical properties under different volumetric fiber contents were obtained. Subsequently, a mesoscopic numerical model of fiber-reinforced concrete that truly reflects the microstructural factors such as aggregate shape, gradation, aspect ratio, fiber distribution, and initial defects was established. By comparing the mesoscopic numerical model with indoor axial tension test results, the mechanism of fiber reinforcement on the tensile strength of concrete was revealed. Finally, the optimal fiber content was analyzed. The results indicate that: Compared to the plain concrete, a fiber volume content of 0.2% is optimal, with the axial tensile strength, split tensile strength, and flexural strength of BFRC increased by 12.81%, 14.79%, and 21.26%, respectively. The error between the tensile strength of the fiber concrete predicted by the established mesoscopic numerical model and the indoor test results for plain (fiber) concrete is 4.24% (5.26%), and the model can accurately reflect the failure development process and macroscopic mechanical behavior of fiber-reinforced concrete specimens. The findings of this study can provide a reference for the design and application of basalt fiber-reinforced concrete structures.

Aiming at the problem of insufficient bearing capacity of tunnel primary support system under unfavorable geology, such as stress concentration zone and broken structural zone, a composite support structure with stud shear connectors arranged at the interface between steel and concrete is proposed. According to the stress characteristics of tunnel support structure, a large eccentric compression test is carried out to explore the failure mode and bearing characteristics of composite support structure, and the bearing capacity of composite structure under different eccentricity conditions is analyzed by numerical simulation. The results show that when there is no stud shear specimen, the separation failure occurs between I-shaped steel and shotcrete. When the stud shear is arranged, the failure mode of steel reinforced concrete structure is concrete cracking and crushing, and the stud shear effectively limits the relative slip between the contact interface of steel and concrete. Compared with the natural bonding condition, the ultimate bearing capacity of the specimens with double-row stud shear connectors increased by 14.79%, and the lateral deflection decreased by 22.94%. The specimens showed better toughness, bearing capacity and bending stiffness. Under the same eccentricity, the arrangement of stud shear connectors can effectively improve the ultimate bearing capacity of the structure, and with the increase of eccentricity, the effect of stud shear connectors on the bearing capacity of the specimen under large eccentric compression is gradually enhanced. The research results can provide theoretical support for the initial support technology of tunnel.

To investigate the impact of changes in end-bearing conditions, resulting from shield tunneling, on the bearing capacity of an upper cement-soil pile composite foundation, this study is conducted based on a specific section of the Zhengzhou Metro Line 5 where shield machines cut through cement-soil piles. According to the principle of similarity, a reduced-scale model test of a single cement-soil pile within a composite foundation was designed for laboratory testing. Based on this, a corresponding finite element analysis model was established. By comparing the results from the reduced-scale model test and numerical simulations, the variation patterns of side resistance and end-bearing resistance of the cement-soil pile composite foundation were analyzed as the pile characteristics changed. Studies indicate after the lower part of the cement-soil pile composite foundation undergoes shield tunneling while maintaining a constant vertical load above, there is primarily a redistribution of stress within individual piles, characterized by a transformation between side resistance and end-bearing resistance to balance the upper load. Simultaneously, the neutral point of the side resistance of the cement-soil pile composite foundation moves downward, and its position relative to the pile length is less than that observed in the case where only the pile length is shortened. The change in the length of the cut pile significantly influences the development of side and end-bearing resistances; the contribution of side resistance decreases with an increase in the cut length, whereas the extent to which end-bearing resistance is mobilized slightly increases as the cut length grows.

Before refracturing, due to the long-term injection and production of old wells, the distribution of regional formation pressure shows non-uniform variations. It is urgent to coupling consider this non-uniform stress evolution in the subsequent refracturing. For this purpose, taking the Chang-6 reservoir in the W block of Changqing Oilfield as an example, an in-situ stress evolution model under long-term injection and production of vertical wells is established using the Fast Lagrangian Analysis of Continua. The simulated stress field is then imported into a hydrofracture numerical model based on the discrete lattice method for modeling fracture propagation of refracturing, achieving an integrated simulation of in-situ stress evolution and hydraulic fracturing evolution. The results show that: (1) After the production of well WJ, the pore pressure around this well decreases by about 4 MPa, and the two horizontal principal stresses experience a similar synchronous reduction, but the decreasing magnitude is only about 2.5 MPa. This indicates that production will result in a decrease in the total stress but an increase in the effective stress. (2) Hydraulic fractures tend to propagate towards the depleted area preferentially. The engineering measures, such as slowly injecting fluid or shutting in before refracturing to increase the formation pressure in the depleted area, are recommended on site, thereby avoiding or reducing refracturing fractures extending into these areas. (3) As the injection time increases, the primary growth of refracturing fractures transitions from area expansion to width expansion, indicating that a short-duration, high-volume refracturing should be adopted. On the one hand, maximizing reservoir transformation can be achieved in a short time, on the other hand, increasing the injection rate can promote the even expansion of multiple fractures.

With the rapid development of infrastructure such as railways, highways, and water conservancy and hydropower projects in the western region of China, a number of extremely complex geological conditions and highly challenging ultra-deep buried tunnels have emerged. These developments place higher demands on the collection, analysis, and application of tunnel geological information. Geological information transparency technology plays a crucial role in ensuring safety, controlling costs, and optimizing construction progress, serving as key technical support for the smooth execution of ultra-deep buried tunnel projects. This paper systematically reviews the current development status of geological information detection technologies, covering remote sensing survey technology, geophysical exploration technology, and directional drilling technology in the pre-construction phase, as well as advanced geological forecasting technology during construction. The application scope and development directions of various technologies are analyzed. The paper also reviews the research status of multi-source geological information fusion technology and 3D geological modeling technology, detailing their progress and challenges in predicting geological conditions, model building, and applications. Finally, this paper looks ahead to the overall development of geological information transparency technology for tunnels: First, establishing a five-dimensional integrated detection system encompassing "space-air-ground-borehole-tunnel" to improve detection accuracy; second, developing intelligent geological monitoring technologies and equipment; and third, based on multi-source data fusion, constructing 3D geological models and applying virtual reality technology to achieve dynamic geological information visualization, thus enhancing the safety and efficiency of tunnel construction.

In the context of the grand construction of the new railway line tunnel project in Sicily, Italy, this article comprehensively and deeply analyzes the complex design and application of the man lock of tunnel boring machine in extreme pressure operating environments. Faced with the arduous task of long-distance crossing of full-section rock formations, especially the unique challenges brought by high-pressure water environments, this article creatively proposes a customized design scheme for the man lock system, aiming to completely solve the safety problem of pressurized entry operations. In response to the functional requirements of the man-lock during pressurized entry operations, and with due consideration given to ergonomics, emergency escape, environmental monitoring systems, etc., the man-lock system configuration was designed to provide equipment-related safety for workers. Finite element force analysis was carried out on the man-lock door and body to verify the structure's strength and ensure it meets working pressure requirements. The structure's stability and reliability were also confirmed through hydrostatic and air-tightness tests. The results of the finite element analysis and pressure tests show that the designed man-lock not only satisfies engineering needs, but also offers strong equipment support for the shield machine's efficient and safe tunneling, ensuring simultaneous enhancement of construction efficiency and safety.

It is quite important for the refined design and construction of geotechnical engineering to obtain a certain amount of borehole data and then determine the stratum profile information through geotechnical investigation. However, due to the particularity of the area where some engineering sites are located (existing old urban areas, cultural Relic Protection Building, etc.), there is often a problem that the borehole data is difficult to obtain, which makes the corresponding stratum information determination challenging. To this end, an artificial intelligence (AI) method for stratum information reconstruction is developed based on the fully convolutional network (FCN). The core idea of this method is to use the existing borehole data in the region as a learning sample, analyze and extract the multi-dimensional information features of the sample (vertical stratification, horizontal extension), and then use this information feature as a template to perform probability-based stratum profile information interpolation reconstruction for engineering sites with only a small amount of borehole data. Through the study and reconstruction of the geological survey data of a tunnel project and foundation pit project in the ancient city of Suzhou, it is found that the accuracy of stratum prediction gradually tends to be stable after the number of simulations increases to more than 30 times, and can reach about 90%. This verifies the applicability of the developed AI reconstruction method of stratum information, which will provide an effective choice for the prediction of complex stratum information in related projects.

The artificial ground freezing method is widely used in underground engineering due to its environmental friendliness, safety, and reliability. This study is conducted based on the connection passage of a section of the Fuzhou metro. Field measurement data and numerical simulation are used to investigate the coupled evolution of temperature and displacement fields of the frozen curtain during the freezing-excavation process. The study results indicate that: A staggered freezing method on both sides was chosen to reduce the strong frost heave impact caused by large-volume freezing. Upon completion of freezing, the surface displacements on the left and right sides were 64.51 mm and 76.72 mm, respectively. Upon completion of the freezing process, the surface displacements on the left and right sides were 64.12 mm and 73.84 mm, respectively. During the excavation, the maximum convergence displacement of the frozen curtain was 1.52 mm, and the maximum displacement convergence rate was 0.082 mm/d, both well below control values. Under varying support timing conditions, deformation and displacement of the frozen curtain increased with extended support timing. The average vertical displacement change at each monitoring point is less than 0.03 mm/d. Increasing the excavation step length from 1.5 m to 2.5 m resulted in the frozen curtain's bottom heave and top settlement increasing by 1.16 times and 5.56 times, respectively. Vertical displacement changes were greater when the excavation step length was between 1.5 m and 2.0 m compared to when it was between 2.0 m and 2.5 m. These findings can be a reference for future freezing-excavation projects of ultra-long subway connecting passages.

At present, the construction of large-span and super-large-span subway tunnels is increasing. Temporary support is often designed to reduce the span in the construction of those tunnels. However, temporary support needs to be removed before secondary lining is constructed due to the spatial overlap between them. The removal of temporary support is the weak situation, because the original stress balance of the structure will be broken. Improper construction can easily cause safety accidents such as tunnel collapse. In view of the lack of systematic research on the structural mechanical response and safety of the super-large-span tunnel constructed by the double-layer initial support arch-cover method at home and abroad, this paper takes the four-line parallel tunnel of Huahua section of Guangzhou Metro Line 11 as the basis project. Through the combination of theoretical analysis and numerical calculation, the mechanical response and safety of the structure during the dismantling of the tunnel are analyzed from both horizontal and vertical aspects. Finally, a scientific, reasonable, safe, efficient and rapid dismantling scheme was determined, and successfully passed the inspection of on-site construction. The results show that it is feasible to dismantle the super-large-span tunnel in urban soft stratum by using the scheme of 'first edge and then middle, and symmetrical demolition in cross direction, first three demolition and one demolition, and then one demolition and one demolition in longitudinal direction', which can provide reference and guidance for subsequent projects.

In order to explore the optimization of air environment and ventilation design parameters in China's extra-long tunnels, this study first analyzed the statistical data of pollutant emission from motor vehicles in China, combined with literature research, and found that the concentration of NO_x in China's tunnels was relatively high, and gradually became the most concerned pollutants in tunnel ventilation. In this study, a field study was carried out in the Yanglin extra-long tunnel in Yunnan. The results show that the peak NO₂ concentration exceeds the ventilation design limit by 2.1 times during the test period, and the emission factors of CO, NO₂ and PM of gasoline vehicles are 0.79 g/(km·veh), 0.04 g/(km·veh) and 10.0 mg/(km·veh), respectively. diesel vehicles are 2.18 g/(km·veh), 1.27 g/(km·veh) and 149 mg/(km·veh), respectively. Compared with the pollutant emission values of domestic and foreign tunnel ventilation design standards, it is found that the current standard values in China are too large. According to the measured emission factors, the required air volume is calculated, and the result is more than 50% lower than the required air volume in Guidelines for Design of Ventilation of Highway Tunnel, which is similar to the required air volume in Standard for the Design of Road Tunnels, and the control item of the required air volume is NO₂ concentration. The results of this study can provide reference for the calculation of pollutant emission and air demand in tunnel ventilation design in China.