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.

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.

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.

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.

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.

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.

To improve the visualization of switch machine status monitoring and the intelligence of fault diagnosis by urban rail transit operators, a 3D visualization monitoring and fault diagnosis method of switch machine based on digital twin is proposed, which provides a powerful technical support for the realtime monitoring of switch machine status, highquality transmission of operation data, and the precise alarm of equipment faults. Compared with the existing intelligent operation and maintenance system of Switch Machines, this study uses digital twin technology to establish a highfidelity model, maps the fieldworking Switch Machines in the information space through realtime interaction of data, and realizes threedimensional visual monitoring of Switch Machines indoors through WebGL and model lightening technology; in view of the small number of samples of fault data for switch machines in the field, it establishes a combined model of CNNTransformer to achieve fault diagnosis. To achieve the fault diagnosis of switch machines, the fault diagnosis accuracy rate is 98.67% under the condition of imbalance between normal data and fault data; In order to verify the feasibility of the proposed framework and the improved algorithmic approach, a 3D visualization monitoring and fault diagnosis platform for switch machines based on digital twins is designed.

Data plays a crucial role in the successful deployment of urban rail transit large language models (LLMs). RetrievalAugmented Generation (RAG) technology emerges as a promising approach for developing industryspecific LLMs and mitigating hallucination issues. However, the lack of comprehensive industry knowledge bases hinders its effectiveness. This study proposes a novel framework for constructing a knowledge graphbased RAG knowledge base for urban rail transit LLMs. This framework consists of four key dimensions: classification skeleton, semantic benchmark, feature rules, and logical relationships. These dimensions are implemented through entity classification systems, terminology dictionaries, attribute libraries, and entity relationship tables, respectively. By incorporating industryspecific attributes for entities, this approach goes beyond the traditional subjectpredicateobject triple structure of knowledge graphs, resulting in a comprehensive and multifaceted representation of industry knowledge. This knowledge base serves as the core component of the RAG system, providing standardized, reliable, and traceable domain knowledge through a systematic pipeline of data collection, structuring, vectorization, and knowledge representation. This process significantly enhances the reliability and domain expertise of the content generated by urban rail transit LLMs, paving the way for a new era driven by both data and knowledge.

Addressing the current challenges in urban rail transit line reconstruction, such as insufficient network synergy, path dependency in equipment updates, and the lack of upgradability design, this study explores theoretical innovation directions. It proposes key strategies, including incorporating upgradability into the equipment performance evaluation system, decoupling equipment from lines for networkoriented reconstruction, and improving the overall network functionality through clustered line reconstruction. These theoretical innovations aim to systematically promote the reconstruction of existing lines, reduce the cost of equipment upgrades, improve maintenance efficiency, and drive the sustainable development of the urban rail transit industry. Based on the framework of Guidelines for reconstruction of existing urban rail transit lines in China, this study addresses critical challenges in urban rail transit reconstruction, including insufficient network coordination, path dependency in equipment upgrades, and inadequate upgradability design. It proposes a comprehensive theoretical framework with four key innovations: integrating "upgradability” into equipment performance evaluation systems; implementing networkoriented decoupling of equipment systems from physical infrastructure; enhancing overall network functionality through clustered line reconstruction approaches; and developing derivative, regenerative, and symbiotic systems for rail transit reconstruction based on the "productionlivingecology" theory of urban renewal. These theoretical advances provide systematic solutions to optimize network functionality, reduce equipment replacement costs, enhance maintenance efficiency, and promote sustainable development in the urban rail transit sector. The proposed framework offers valuable guidance for policymaking and implementation strategies in urban rail transit modernization.

With accelerating global urbanization, traditional rail transportation faces challenges in capacity bottlenecks and the need for efficiency improvements. The development of the lowaltitude economy, particularly Unmanned Aerial Vehicles (UAVs) and electric Vertical TakeOff and Landing aircraft (eVTOLs), provides new solutions for rail transportation systems. This paper explores the integration of the lowaltitude economy with rail transportation, analyzing its potential in improving urban traffic efficiency and promoting the development of smart cities. The paper discusses the key technologies and practical applications of the integration f perspectives: integration motivation, technological foundations, and application scenarios. By introducing visual perception, communication, control, multisensor fusion, and safety technologies, the lowaltitude economy can enhance inspection efficiency, construction monitoring, and emergency response capabilities within rail transportation systems. This paper aims to provide a practical discussion on the integration of the lowaltitude economy and rail transportation, further advancing the development of smart city transportation systems.