Subways, as a primary component of urban public transportation, harbor particulate matter within their microenvironments that pose health risks to commuters. To enhance the health of individuals during their subway commutes, a study was conducted to analyze the spatiotemporal heterogeneity of fine particulate matter (PM_2.5) concentrations in the subway microenvironment. The results show that: The PM_2.5 concentration in underground train carriages on weekdays (113.67 μg/m³) is higher than on non-working days (47.62 μg/m³), and the PM_2.5 concentration in underground train carriages is significantly higher than in above-ground and elevated sections (seven times higher) ; lines constructed earlier have higher PM_2.5 concentrations than newly built lines; the PM_2.5 concentration on platforms exhibit a cyclical trend with the arrival and departure of trains; fully enclosed screen doors are more effective than full-height security doors in controlling the accumulation of particles; the PM_2.5 concentration during off-peak hours (75 μg/m³) is lower than during peak hours (102 μg/m³). Furthermore, the study analyzed the potential impact of off-peak travel strategies on the PM_2.5 exposure levels of commuters, the results suggests that off-peak travel could reduce exposure by 25.58% during a single commute. The results of the study provide data support for the prevention.

Underground Logistics System (ULS), as a subterranean urban infrastructure with public utility attributes, can effectively meet urban emergency demands through highly resilient freight networks. However, the operational mechanisms and performance assessment methods for ULS in complex emergency logistics scenarios remain underdeveloped. This study examines ULS emergency service capacity, focusing on the impacts of the operational environment, network structure, and scheduling. A model measuring efficiency, effectiveness, and fairness is developed. Simulations based on freight demand and surface road damage, using the Xianlin case in Nanjing, compare ULS and surface truck delivery. Results show that: ULS exhibits significant advantages in emergency freight performance, particularly under conditions of surface traffic congestion and narrow emergency response time windows. Furthermore, increasing node logistics redundancy, optimizing end-point delivery modes, and ensuring local freight fairness are identified as key factors in enhancing ULS emergency service capacity. This research advances ULS planning theory and offers new insights for urban emergency management.

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.

Understanding the resistance coefficient along the tunnel wall is helpful to optimize the ventilation design of tunnel construction and improve the rationality of ventilation scheme. The influence of the height, shape and spacing of rough elements on the resistance coefficient along the tunnel wall is studied. Through the model test and the numerical model, the difference between the empirical formula and the numerical simulation results was explored. The results show that: With the higher height of the rough element on the tunnel wall, the influence on the resistance coefficient along the tunnel wall is less. The shape of rough elements on the tunnel wall has a great influence on the resistance coefficient along the tunnel, and the semi-spherical rough elements have the smallest resistance coefficient along the way. Comparing the calculated results of empirical formula with the numerical simulation results, the difference between them is relatively stable, which is related to the height of rough elements. The correction coefficient α is proposed for the empirical formula, and the corresponding relationship between α and the average roughness height Δ of the wall is α = 1.29+0.024 8Δ.

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.

The reloading mechanical properties of the surrounding rock in an underground energy storage cavern are crucial for determining the safety of underground energy storage projects. This study conducted triaxial loading and unloading tests on mudstone, as well as reloading tests on unloaded damaged mudstone. By employing testing and analysis techniques such as nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), the research investigated the impact of unloading effects on the reloading mechanical properties of mudstone and revealed the deterioration mechanisms of reloading damaged mudstone. The results indicate that the fractal dimension ultimately decreases as confining pressure increases, and the confining pressure's control over internal micro-cracks in the mudstone becomes more pronounced. With increasing unloading damage, small-size micro-pores inside the mudstone samples develop into medium-sized pores, resulting in a higher internal porosity. The greater the initial unloading damage, the larger the reduction in reloading strength of the mudstone. The degree of unloading damage progressively affects the failure mode of rock samples, transitioning from shear failure to shear-tensile failure, and eventually to tensile-shear failure with increasing unloading damage. A correlation between unloading damage degree, porosity, and reloading strength has been established, bridging the gap between microstructural damage and macro-strength deterioration in unloaded damaged mudstone. This finding provides a reference for delineating unloading damage zones and predicting reloading strength within unloading areas.

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.

Microwave radiation, as an emerging rock-breaking technology, shows promising applications in assisting mechanical rock fragmentation. To explore the damage mechanisms of microwave radiation on quartz sandstone, this study investigates the variations in uniaxial compressive strength, wave velocity, and macro-microscopic damage characteristics of quartz sandstone under different microwave powers and exposure times. The results indicate that with increasing microwave power and exposure time, the uniaxial compressive strength and elastic modulus exhibit a decreasing trend, while peak strain gradually increases. Both P-wave and S-wave velocities show an overall decline. The damage factor shows an upward trend, and the longer the radiation time, the greater the increase in the damage factor. As microwave power and exposure time increase, the degree of quartz sandstone fragmentation significantly intensifies, resulting in smaller and more numerous fragments. The failure mode shifts from a single shear failure to shear and cleavage along fragile planes. SEM images and fractal dimension (D-value) results indicate that as microwave exposure time increases, the number, length, width, and depth of internal cracks in specimens show an increasing trend, evolving from initial single cracks to superimposed fractures.

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.

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.