To ensure the structural safety of existing shield tunnels during nearzero distance deep excavation and address the challenges of retaining structure construction and ground reinforcement under low clearance conditions, this paper presents a case study of a pump station excavation project in the Yangtze River floodplain area. The protection measures include Metro Jet System (MJS) piles with Hsteel insertion using highfrequency hydraulic resonancefree hammer, and synchronous prereinforcement inside the shield tunnel using longitudinal braces and filament wound profiles. Through comparative analysis of threedimensional numerical simulation and field monitoring data before and after deep excavation, the soil squeezing effect and timespace effect on the tunnel structure were effectively controlled. These findings can provide valuable reference for the design and construction of similar excavation projects.

Bidirectional substations have advantages in regenerative braking energy utilization of urban rail transit because of their controllable output voltage, capability of unity power factor operation, and bidirectional energy flow. Due to voltage sensor errors and line parameter inconsistencies, the two converters in the substation generate significant unbalanced currents. While increasing the converter output current feedback coefficient can reduce the current difference between converters, it consequently intensifies the output voltage fluctuations of the substation. On the basis of droop control strategy based on converter output current feedback, a droop control strategy based on substation output current compensating voltage command value is proposed by adding a voltage compensation term proportional to substation output current. The results show that this strategy can improve the current balance between converters and reduce the fluctuation degree of substation output voltage. Finally, the simulation model is built in MATLAB/Simulink, and the example analysis is carried out to verify the effectiveness of the proposed strategy.

This paper addresses the issues of inefficient recovery of regenerative braking energy, limited substation power supply capacity, and insufficient response to emergency traction in urban rail transit when using single energy storage systems. The research focuses on the application scheme and technical advantages of a supercapacitorlithium titanate battery hybrid energy storage system. First, by comparing supercapacitors, lithium titanate batteries, and flywheels in terms of key parameters such as power density, energy density, and cost, energy storage media are classified into two categories: powertype and energytype. Then, simulation results demonstrate that the hybrid energy storage system composed of supercapacitors and lithium titanate batteries outperforms single energy storage solutions in terms of recovering regenerative braking energy, enhancing substation power supply capacity, and providing emergency traction capabilities for trains. Based on this analysis, the study highlights the application potential of the supercapacitorlithium titanate battery hybrid energy storage system in urban rail transit, particularly its notable advantages in regenerative energy utilization technologies.

In order to analyze the development and current research status of urban rail transit network performance evaluation, in urban rail transit networks this paper conducts a quantitative analysis of the literature from the CNKI database based on CiteSpace software. This paper gradually focuses on three levels of research: urban rail transit, urban rail transit network, and urban rail transit network performance evaluation, and analyzes the information such as the number of publications, authors, literature sources and keywords. By tracing the important literature, the main indicators of rail transit network performance evaluation are summarized, and the advantages and disadvantages of different evaluation methods are commented. The results show that the research on performance evaluation of urban rail transit networks is undergoing several important transformations. Firstly, the analytical model is developed from unweighted network to weighted network model, which pays more attention to the differences between stations and intervals. Secondly, the research object was extended from the analysis of rail transit network to the comprehensive evaluation of coupled transportation networks such as railroad and railbus. Finally, the research focus of network performance has gradually shifted from the resistance ability under disasters or external shocks to the resilience evaluation including the postdisaster recovery ability.

Unreasonable grounding system can cause problems such as increased train axle potential and circular current, as well as bearing erosion, deteriorating the electromagnetic environment of onboard electronic equipment, and thus pose a threat to the safety of train operation. Therefore, it is necessary to design the train grounding system appropriately. First, uniform chain circuit model is used to model the traction power supply system and dual current train grounding system. Secondly, through traction and power supply calculations, the train current can be obtained. Taking train current as the excitation source, the distribution of train axle voltage and circular current can be obtained. Take the currents of grounding resistors as a measure of the vehicle circular current distribution. Finally, PSO algorithm is used to optimize the train grounding system. After the optimization, the maximum circular current decreases by about 20%, and the maximum vehicle axle voltage declines slightly. The optimization of the train grounding system in this article presents a guide for the design of the grounding system for dualsystem trains, as well as provides a reference for other trains.

In response to the problem of setting rail cant under the dynamic changes of subway wheel profile, this paper measured the wear profile data of LM wheels at four operating mileage, established a subway vehicle system dynamics model, and analyzed the influence of rail cant on the vehicle's straightline stability and curve passing performance considering during the dynamic changes of wheel profile. The entropy weight method is used to comprehensively evaluate the dynamic performance of the vehicle, and the optimal rail cant setting scheme is obtained for straight lines and curves with different radii considering under the dynamic changes of the wheel profile. Research has shown that when a vehicle is running in a straight line, the coupling of rail cant and wheel wear profile has a more significant impact on lateral stability than vertical stability. The dynamic changes in the wheel profile exacerbate the impact of rail cant on vehicle stability. During the curve operation, when rail cant is constant, the vehicle's curve negotiation performance first deteriorates, then improves, and then deteriorates as the wheel wear profile dynamically changes; When the wheel wear profile is constant, as the curve radius increases, the influence of the rail cant on the vehicle's curve negotiation performance gradually increases. Taking into account the dynamic changes in the wheel profile, the optimal matching of the outer/inner rail cant for straight, R300 m, R400 m, R500 m, and R600 m curve is (1/30, 1/40),(1/20, 1/20), (1/20, 1/40), (1/40, 1/40), and (1/40, 1/40), respectively.

To investigate the diffusion mechanism of backfill grouting slurry in metro tunnels under different working conditions during the operation period, a mathematical model of the diffusion process was derived based on the physical processes involved in grouting. A threedimensional numerical simulation program, developed using the finite element method (FEM) and the volume of fluid (VOF) method, was applied. Using an actual project during the operation period as a case study, the diffusion behavior of backfill grouting in metro tunnels under different soil conditions was simulated, and the rationality of the numerical simulation results was validated through laboratory model tests. The results indicate that in hard soils, the slurry predominantly fractures in a direction perpendicular to the lining structure, making it difficult to form a large closed reinforcement area behind the lining. In contrast, in soft soils, as the grouting pressure increases, the slurry gradually spreads along the interface between the tunnel and the soil. Upon completion of grouting, the slurry forms a uniformly distributed closed reinforcement along the tunnel wall. The consistency between the model test and numerical simulation trends confirms the reliability of the grouting diffusion mechanism behind the tunnel wall.

This study investigates the unsteady aerodynamic characteristics of urban trains passing through most criticallength tunnels through numerical simulations. The threedimensional unsteady Reynoldsaveraged NavierStokes (RANS) equations coupled with the Renormalization Group (RNG) kɛ turbulence model were employed to analyze the aerodynamic behavior of an urban train operating at 160 km/h. The results reveal that train operation significantly modifies the flow field structure and pressure distribution within the tunnel, characterized by distinct regional patterns. These modifications are primarily attributed to two factors: the propagation and reflection of traininduced pressure waves, and the compression effect of the train body on the tunnel air. Significant differences are observed between pressure variations on the train surface and tunnel wall monitoring points. While the train surface pressure is predominantly influenced by the arrival timing of compression and expansion waves, the tunnel wall pressure exhibits more complex evolution patterns due to the combined effects of train disturbances, pressure waves, and lowpressure regions. The aerodynamic drag is mainly pressureinduced and significantly affected by both blockage effects and pressure waves. Furthermore, distinct unsteady aerodynamic responses are observed among different car bodies: the first three cars are primarily affected by entrance and exit disturbances, while the rear five cars experience additional pressure wave effects, resulting in substantial fluctuations in lateral force, rolling moment, and yawing moment.

During subway train operation in tunnels, piston wind is generated, which significantly affects the tunnel flow field. Understanding piston wind characteristics is crucial for its effective utilization. It is of great significance to study the characteristics of piston wind for rational utilization of piston wind. Based on Bernoulli equation of unsteady flow, a lumped parameter theoretical model of piston wind in subway tunnel is established, and the characteristics of unsteady piston wind are analyzed. In order to verify the accuracy of the theoretical model, a reduced size model test bench of 1:16 was established, and the piston wind speed was tested experimentally. The comparison between the model value and the measured value shows that the Pearson correlation coefficient is higher than 0.98, and the average error is lower than 13%, which verifies the correlation and accuracy of the theoretical model. By using the lumped parameter theory model, the influence of different factors on the piston wind in subway tunnel is explored, and the grey correlation degree is analyzed. The results show that the congestion ratio is the biggest factor affecting the ventilation effect of the tunnel piston, followed by the train length and train speed, and the tunnel length is the least. Based on this, a fitting formula for the ventilation effect of the piston in common subway tunnels in China is proposed.

The fully automatic operation (FAO) system has become the mainstream of urban rail transit in China. Considering factors such as safety and timeliness of emergency response, at present, FAO lines in China still operate in a staffed manner, failing to give full play to the fully automatic advantage. To address the concerns of operation units and improve the efficiency of emergency response for equipment failures, this paper proposes an emergency plan framework related to FAO line directed by key equipment based on extensive survey on the current emergency plans of fully automatic operation lines in multiple cities. Aiming at the problems of insufficient completeness and poor operability of current emergency plans, a design method of emergency plans for fault handling that integrates failure mode analysis (EMEA) and entropy weight method (EWM) is proposed. Considering five factors such as the severity, occurrence probability, scope of influence, difficulty of isolation, and difficulty of operation restoration, objectively calculate the comprehensive fault impact index, combined with system design information and operation log data. Based on this impact index, operators can determine the fault handling strategy and design the emergency plans. Finally, taking the axle counter equipment as an example, the equipment fault mode is classified and an emergency plan is designed targeted with 85 months of fault log data of a certain line. The results show that the completeness and operability of the failure handling emergency plan have been effectively improved.