Research purposes: The static lateral pressure coefficient is a key parameter in the design of metro, foundation pit and other engineering projects. In-situ testing enables direct measurement of the coefficient of earth pressure at rest with minimal or no disturbance to the soil structure, yet the applicable scope of different testing methods remains unclear. To determine the range of values and empirical formulas for the static lateral pressure coefficient of loess in Xi'an, lateral compression test, flat chisel lateral dilation test, and static cone penetration test were conducted in the loess strata of typical Xi'an metro lines, and the field test results were compared with those from laboratory tests.
Research conclusions: (1) The static lateral pressure coefficient of loess obtained by the lateral compression test was close to the laboratory test results. (2) Based on the results of flat chisel lateral dilation test and the existing calculation formula, an empirical formula for calculating the static lateral pressure coefficient of loess in Xi'an was proposed through fitting, using the product of power function of horizontal stress index and the constant. (3) The normalized cone tip resistance of static cone penetration test was approximately linearly related to the static lateral pressure coefficient measured in indoor test. (4) The relevant results can provide reference for measuring the static lateral pressure coefficient of loess in Xi'an.

Research purposes: In recent years, underground rail transit has expanded rapidly, however, most metro foundation pit projects are constructed in urban core areas with complex geological conditions and environmentally sensitive surroundings, posing multiple challenges such as complicated adjacent environments, limited construction space, and stringent deformation-control requirements. Therefore, effectively controlling the effects of foundation pit excavation on retaining structures and the surrounding environment has become an urgent issue. Using a semi-covered excavation deep foundation pit project for a metro station in Jinan as a case study, this paper systematically investigates the deformation behavior of the diaphragm wall and surface settlement during excavation through numerical simulation and field monitoring.
Research conclusions: (1) Foundation pit excavation exhibits pronounced spatial effects: the incremental horizontal displacement of the diaphragm wall is strongly and positively correlated with excavation depth, and the maximum horizontal displacement in this project ranges from 0.045%H_e to 0.084%H_e. (2) During the integrated construction of the eastern and western foundation pits, excavation of the eastern pit causes a marked increase in diaphragm wall displacement in the adjacent area of the western pit, whereas its effect on the non-adjacent diaphragm wall is limited. (3) Ground surface settlement outside the pit exhibits a typical groove-shaped distribution, with an influence zone extending approximately 3H_e from the excavation. Owing to variations in wall deformation modes, both the magnitudes and locations of the maximum settlement differ among monitoring points. In the soft-hard interbedded strata, the ratio between the maximum horizontal displacement of the diaphragm wall and the maximum ground surface settlement ranges from 0.32 to 1.05. (4) These findings provide reference for the design and construction of similar metro foundation pit projects in soft-hard interbedded strata.

Research purposes: Pixel-level rail segmentation based on computer vision serves as a prerequisite step for railway track condition detection. Although deep learning methods have demonstrated promising performance in image segmentation tasks, traditional convolutional encoder-decoder architectures, due to stacked convolution and pooling operations, tend to lose spatial feature information of the target, thereby limiting further improvement in segmentation accuracy. This paper aims to design a long-distance spatial feature extraction network to capture the feature dependencies of rails across long-distance spatial contexts and overcome the limitation of traditional methods that can only extract local features.
Research conclusions: (1) The proposed long-distance spatial feature extraction network, which collaboratively processes data through an encoder, a long-distance spatial feature extraction module, and a decoder, effectively enhances the modeling capability for spatial feature information of rails. (2) The long-distance spatial feature extraction mechanism significantly improves recognition accuracy by performing weighted averaging of responses from all rail-similar pixels within the current image and across adjacent images. (3) Experimental results on the dataset collected by the Railway Administration demonstrate that the proposed method achieves a Dice coefficient of 0.875, RAVD of 0.166, ASSD of 12.738, and MSSD of 58.200, indicating excellent segmentation performance. (4) The research findings can provide theoretical guidance for the automatic division of track protection zones by railway maintenance departments.

Research purposes: To investigate the role of shear hinges in floating slab systems to guide their optimized design, taking two types of floating slabs from Shanghai metro lines as examples, a finite element model of the track-floating slab system was established. A static analysis method based on moving loads was adopted to conduct in-depth calculations and analyses of the floating slab system under different vibration isolator failure conditions, supplemented by dynamic calculations for verification. Through quantitative analysis of the responses of the floating slab system under different vibration isolator failure conditions, the reasonable constraint stiffness of the shear hinge and the optimized shear hinge design were obtained.
Research conclusions: (1) The influence laws of shear hinge stiffness reflected by the two types of floating slabs are basically the same, with no significant differences. (2) Compared with the vertical bending stiffness of the shear hinge, the vertical stiffness has a more significant impact on the floating slab system, and there exists a reasonable value (about 90 MN/m). A value lower than this may lead to excessive uplift force on the fasteners of the floating slab. (3) Under the reasonable constraint stiffness of the shear hinge, the dynamic response of the train and of the floating slab system can meet the requirements. The failure of the vibration isolator has no significant impact on the dynamic response of the train, but has a significant impact on the dynamic response of the floating slab system. (4) Based on the reasonable constraint stiffness, all three types of shear hinges can provide sufficient vertical stiffness when two pairs are set. The reasonable plate thickness (or steel hinge rod diameter) of the upper-mounted flat plate type, side-mounted flat plate type, and upper-mounted steel hinge rod type shear hinges is approximately 20 mm, 40 mm, and 20 mm, respectively. (5) The research results can provide a reference for the standardization and optimized design of shear hinges in floating slabs in actual engineering.

Research purposes: The prefabricated short floating slab track technology connected by shear hinges has been widely used. It has been proved to be successful over years of practical application, but still has shortcomings such as an increased number of components that add to maintenance workload, and reduced integrity and stability compared with long slabs. To address these issues,this study combines the advantages of both prefabricated short and long slabs, utilizing prefabrication technology while reducing weak points such as slab joints,it conducts research on assembled wet-joint long floating slab tracks, and their engineering performance is verified through multiple tests.
Research conclusions: (1) Using high toughness wet-joint concrete materials, prefabricated short floating slabs of 3.6 m or 6 m can be connected to long floating slabs of over 25 m with a joint width of 300 mm. (2) The laboratory full-scale test verifies that the strength and fatigue performance of the post-cast wet joints can meet the requirements of actual service conditions. (3) In the practical engineering application, the wet-joint long floating slabs demonstrate good vibration reduction performance, and the joints remain in good condition after four years of operation. (4) The research results can be applied to sections of rail transit with complex line conditions—such as small-radius curves, continuous reverse curves, and steep gradients—and areas with high vibration reduction requirements.

Research purposes: Steel truss arch bridges with separated girder systems exhibit substantial structural rigidity and favorable seismic performance. However, the arch-crossbeam joint at the arch base features an intricate interlaced arrangement of transverse and longitudinal diaphragms, resulting in complex mechanical behavior and load transfer mechanisms. To investigate the structural response characteristics of the arch-crossbeam joint under seismic and other operational conditions, based on the Beijing-Hangzhou Grand Canal Bridge of the Weifang-Suqian Railway with a main span of 300 m in a high seismic intensity zone, this paper employs localized refined simulation analysis to study the arch-crossbeam joint's mechanical properties, stress distribution patterns, and force transmission mechanisms.
Research conclusions: (1) Under rare earthquake conditions, the structural load effect is more significant, and the stress level of the plates is higher than that under the main-plus-auxiliary load case by 60% to 130%. The stress concentration of the joint is distributed at the junction of the arch web plate and the bridge deck, as well as at the locations of geometric changes and support constraints. The maximum stress at the junction between the bottom of the outer arch web and the crossbeam under rare earthquakes reaches 450 MPa, which is still within the safe range. (2) The stress distributions of the arch rib plates under the two working conditions are generally similar, gradually decreasing along the arch axial direction from the bridge deck upward. The stress exhibits local peak distributions along the axial direction due to the influence of diaphragms. Among these, the web of the arch rib experiences the most unfavorable stresses, with a maximum stress reaching -429 MPa. The stresses in the webs on both sides of the arch rib are markedly greater than those in the internal webs, establishing them as the primary load-bearing components. Stresses in the vertical direction for the top and middle welds, as well as the crossbeam bottom plate, are approximately zero, confirming that the joint primarily transmits horizontal loads. (3) Under two working conditions, the outer arch rib web plates transmit 53.6% and 52.0% of the horizontal force, respectively, being the main force transmitting components. The internal arch rib web plates transfer less than 10% of the load, indicating weak force transmission. The arch rib crossbeam welds transmit 97.2% and 96.6% of the horizontal force through shear, respectively, making them the main ways of horizontal force transmission. (4) The research findings offer valuable insights for optimizing the design of long-span arch-girder composite bridges in high seismic intensity regions.

Research purposes: Health monitoring of high-speed rail steel truss bridges is essential for operational safety, while the unique nature of railway operations limits available methods. How to accurately extracting structural characteristic indicators from limited data is a key challenge for intelligent operation and maintenance. This paper aims to improve the health monitoring efficiency of high-speed railway steel truss girder bridges, proposing the statistical steady-state static strain characteristic function as a novel structural indicator. A digital twin finite element model integrating random train loads is built to simulate structural response. A targeted algorithm for extracting the characteristic function is designed, and the distribution pattern of this function within the structural configuration space is systematically revealed. Lightweight neural networks are used to validate the effectiveness and representational capability of the proposed indicator. The research seeks to address the technical challenges associated with existing monitoring indicators, providing a new approach for structural state assessment and damage identification.
Research conclusions: (1) The established statistical steady-state static strain characteristic function theoretical model decouples load from structural parameters, enabling representation of the static structural characteristics of the structure. (2) The proposed three-level extraction algorithm effectively resolves issues such as noise aliasing and inconsistent spatio-temporal scales in monitoring signals, achieving precise extraction of the characteristic function. (3) The lightweight 1D-CNN model achieves accurate quantitative validation, confirming the strong representational capability of the characteristic function for the spatial locations of measurement points. (4) The findings of this study can provide technical references for the research on the health monitoring of high-speed rail bridges.

Research purposes: Steel rail fasteners are crucial components that connect tracks to bridges, directly impacting the interaction forces between them and playing a significant role in the seismic performance of railway bridges. This paper investigated the seismic response characteristics of a heavy-haul railway train-track-bridge (HHRTTB) system under varying fastener resistances and track constraint conditions. A 5-span heavy-haul railway bridge was selected as the research subject, and a refined simulation model of the HHRTTB system was established using ANSYS/LS-DYNA. The study quantitatively evaluated the safety of bridge components and trains under seismic excitation.
Research conclusions: (1) The track structure provides additional restraint to the bridge, effectively reducing its seismic response. As the fastener resistance increases, the peak longitudinal and transverse curvatures at the base of the bridge piers decrease by 8.9% and 1.7%, respectively. (2) Compared to the piers, the response of the bearings is more pronounced, with peak longitudinal and transverse displacement reductions of 27.3% and 14.0%, respectively. The increase in fastener resistance has a more significant effect on the longitudinal seismic mitigation of the bridge. (3) The lateral restrainers become ineffective after the fixed bearings fail, resulting in a 12.1% reduction in peak collision force. The maximum reductions in track deformation and train wheel lift are 20.4% and 23.4%, respectively, indicating that the increased stiffness of the fasteners reduces the risk of train derailment to some extent. The structural response tends to stabilize when the fastener resistance reaches 24 kN/m. (4) These research findings offer valuable references and insights for the seismic design of track structures on heavy-haul railway bridges.

Research purposes: Large deformation is a core challenge faced in tunnel construction worldwide, especially for tunnels overlying deep-loose soft rock. Dangerous situations caused by large deformation and damage to tunnels occur frequently, resulting in high construction risks and considerable construction difficulties. Based on a tunnel project under construction, the characteristics and causes of the large deformation and failure of the initial support of the tunnel, as well as the effectiveness of different support control technologies were analyzed. Deformation control measures suitable for this tunnel were proposed and verified on site, providing a reference for deformation control in similar tunnels with loose and weak surrounding rock.
Research conclusions: (1) Loose surrounding rock tunnels mainly exhibit deformation and failure characteristics in six aspects: fast deformation rate, large deformation amount, long duration, susceptibility to excavation disturbance, tunnel face shaping and extrusion, and large surrounding rock loosening range. (2) This paper compares the mechanism and characteristics of different surrounding rock deformation control technologies, and combines the deformation and damage characteristics of tunnel surrounding rock to propose a hierarchical control technology for surrounding rock deformation suitable for the tunnel. (3) According to the surrounding rock deformation control limits at each construction stage, corresponding control measures are taken on site. The surrounding rock deformation time history curve changes from "4 stages" to "3 stages". The stable deformation stage is entered as early as possible, and the support and surrounding rock deform in coordination with each other, thereby achieving the purpose of "active control" of surrounding rock deformation without causing support redundancy, which is more economical and reasonable. (4) This study can provide a reference for deformation control of tunnels in similar loose and weak surrounding rock.

Research purposes: In response to frequent diseases such as misalignment of the tunnel invert and mud pumping during the operation of railway loess tunnel, this paper takes a loess surrounding soil section of a tunnel on the newly built Lanzhou‒Hezuo Railway as the research object, considering that the loess at the invert base of the tunnel will be in a water-rich state following the opening of the tunnel. Based on dynamic triaxial tests and numerical simulation, the effects of cyclic train loading on the dynamic pore water pressure and dynamic strain of surrounding soil under the tunnel invert are analyzed, aiming to reveal a new formation mechanism of substrate disease of loess tunnels triggered by train vibration.
Research conclusions: (1) The liquefaction characteristics of the surrounding soil at the base are significantly influenced by the axle load and running speed of train. (2) The static shear ratio α_s of the tunnel base surrounding rock is the key factor affecting the liquefaction, and subsequent research and engineering control should focus on the shallow buried section and the sections with insufficient invert thickness. (3) When the surrounding soil under the invert of tunnels partially liquefied, the cumulative load of trains will further enlarge the liquefied area, and then the invert structure with a liquefied base will appear cumulative fatigue tension cracking. (4) This study provides a theoretical basis for the formation mechanism of substrate liquefaction diseases of loess tunnels, and can offer technical criteria and references for the safety assessment and disease prevention and control of railway tunnels.

Research purposes: There are abundant research results on the correction coefficient for external water pressure in tunnels, but there is some disagreement regarding its definition and influencing factors. The disagreements mainly focus on the following issues: whether the empirical value of the correction coefficient in relevant specifications primarily considers the permeability of surrounding rock or the influence of tunnel lining, and whether the correction coefficient for external water pressure in fully blocked tunnels is 1, etc. This article analyzes the influencing factors of the external water pressure correction coefficient and the value rules of each factor by tracing the concept and sorting out existing research results.
Research conclusions: (1) The correction coefficient for external water pressure is the result of the comprehensive influence of the initial seepage field, lining permeability, and anti-seepage and drainage measures. (2) For fully blocked tunnels without considering surrounding rock drainage (blocking) measures, the external water pressure correction coefficient equals the rock permeability correction coefficient. (3)The correction coefficient β₁ is not a fixed value, but varies with the fluctuation of the water level. (4) When tunneling through hydrogeological conditions involving valley floors, riverbeds, and confined aquifers, the correction coefficient β₁ may exhibit values ≥1. (5) During the survey phase, the primary factor considered for determining the correction coefficient for external water pressure is the surrounding rock seepage field, which can be calculated using the standard lookup table method. When necessary, using long-term observation holes for actual measurement or using 3D modeling analysis of the seepage field can improve the rationality of the correction coefficient. (6)The research results can provide a reference for determining the external hydraulic pressure correction coefficient for similar tunnel projects.

Research purposes: The signal systems of the early high-speed railways in China are about to enter a major overhaul and renovation cycle. The renovation is a complex project involving multiple systems and specialties. Conducting research on the technological transformation of the existing signal systems of high-speed railways, and systematically addressing the key technical issues throughout the entire process—from current situation assessment and scheme design to construction and testing verification—hold significant theoretical value and practical significance for ensuring the long-term safe and efficient operation of China's high-speed railway network and promoting the independent upgrading of technical equipment.
Research conclusions: (1) Driven by multiple factors including the iteration of technical standards, equipment service life characteristics, and safety assurance requirements, China's early high-speed railway signaling systems have entered the window period for technical renovation. (2) For the key technologies involved in the signaling system renovation of existing lines, clear engineering renovation schemes and implementation paths are proposed. (3) By adopting the engineering mode of "one-time design, phased implementation, step-by-step commissioning", combined with the two-tier verification system of "full-function verification through in-factory simulation, on-site tests focusing on real-train dynamic testing", systematic functional and interface problems can be identified and resolved at the in-factory stage, which effectively reduces the on-site renovation risks for operating lines. (4) The results of this research have been verified in the renovation practices of multiple lines, and can provide a referable technical framework for the subsequent batch renovation of signaling systems on existing high-speed railway lines across the country.

Research purposes: The expansion and speed increase project of Changchun-Baicheng Railway has brought about the problem of electromagnetic influence from the traction power supply system on the weak-current system's information transmission cables under direct power supply mode. Long-term exposure of cables to high magnetic induction longitudinal potential will cause interference to information transmission and the monitoring and control of weak-current systems, posing a serious threat to train operation safety. From the perspective of operation and maintenance, unstable induced longitudinal potential on cables will increase the failure rate of associated equipment and modules, accelerate equipment aging, and pose a danger to the operation and maintenance personnel. Therefore, it is necessary to conduct systematic testing and effective interference protection on this issue to ensure that the weak-current system's information transmission cable is not affected by electromagnetic interference and to ensure railway transport safety.
Research conclusions: (1) The induced longitudinal potential generated on weak-current cables is caused by the traction current of the traction network. (2) Through on-site testing and data analysis, it's found that for every kiloampere of traction current, the induced longitudinal potential generated on a unit length of information transmission cable is about 33-34 V. (3) The induced longitudinal potential generated on the cable needs to be shielded. After testing and analysis, effective shielding protection technology and equipment can achieve a shielding coefficient of less than 0.2 with a 91% probability. (4) The research results can provide a reference and basis for evaluating the degree of electromagnetic interference on information transmission cables of weak-current systems under direct power supply mode and cable protection design.

Research purposes: The discomfort and environmental pollution caused by subway vibration and noise have attracted widespread attention from society. At present, China is vigorously developing prefabricated concrete buildings. Before the completion and opening of the subway, it will be particularly important to predict the vibration response and comfort evaluation of prefabricated structures under subway vibration excitation, taking into account the unique semi-rigid mechanical characteristics of dry connected prefabricated concrete frame structures.
Research conclusions: （1）This paper establishes a three-dimensional finite element model of the track bed, tunnel, soil, and prefabricated concrete frame structure, and verifies the accuracy of the model through experimental data comparison. （2） On this basis, this article systematically studies the dynamic response characteristics and comfort evaluation of semi-rigid prefabricated concrete frame structures under subway vibration, and explores the influence of various key factors, including node rotation semi-rigid, structural height, distance between the structure and the subway line, train operating speed, and soil properties. （3） Based on the dataset obtained from numerical simulation, this paper uses BP neural network for model training and hyper-parameter optimization, and introduces transfer learning method. The dataset is divided into training, validation, and test sets in a 6∶2∶2 ratio.（4）A visual interaction platform based on PyWebIO is developed to enable rapid prediction of the maximum Z-vibration level and ride comfort of prefabricated concrete frame structures subjected to subway-induced vibrations.（5）This research can provide a reference for vibration comfort of prefabricated structures with semi-rigid connections induced by subway.

Research purposes: To address the mismatch between existing railway green development studies and Jiangsu's unique conditions, this paper analyzes the current status and core issues of Jiangsu's intercity railway green development under its dual-carbon goals and transport powerhouse construction needs, and proposes targeted strategies to support its green low-carbon transformation.
Research conclusions: (1) Five core issues in Jiangsu intercity railway green development are identified: unbalanced transport structure, high traction energy consumption, insufficient energy-saving measures, lagging new energy technology promotion, and weak green standardization. (2) Drawing on green railway experience from Japan, Germany, France, and the US, as well as domestic benchmarks (Beijing-Zhangjiakou, Beijing-Xiong'an intercity railways, Hangzhou West Station), a five-dimensional adaptive strategy is proposed: optimizing transport structure, promoting multimodal transport, reducing traction energy consumption, implementing green energy-saving measures, expanding renewable energy application, and strengthening green railway standardization. (3) This strategy fits Jiangsu's green railway development reality, offers a feasible path for its green transport system construction, and has high promotion value for national railway green development.

Research purposes: Urban rail transit is a critical infrastructure system supporting urban spatial organization and public transportation. However, during its civil construction stage, it involves intensive material inputs and high energy consumption, making it a key sector that urgently requires refined carbon-emission identification in the context of low-carbon transformation. Focusing on carbon emissions from civil engineering works during the construction period of urban rail transit lines, this study develops a carbon emission intensity indicator system and accounting model for unit projects based on life cycle assessment theory. An empirical assessment is conducted using six stations and ten tunnel sections of a selected rail transit line as the research objects. Furthermore, the study analyzes the composition of emission intensity at the levels of divisional works, sub-divisional works, and sub-items, revealing the emission differences among different stations and tunnel sections as well as the mechanisms underlying these differences.
Research conclusions: (1) The total carbon emissions during the construction period of the civil engineering works of the case line amount to 2.289 408 million tCO₂eq, with station works and tunnel section works contributing 47.53% and 52.47%, respectively. (2) The ratios of direct emissions to energy-related indirect emissions for station works and tunnel section works are 2.13∶1 and 1.39∶1, respectively, indicating that electrically driven machinery accounts for a higher proportion in section works than in station works. (3) The emission intensity of station works is mainly concentrated in the main and enclosure structures, which together account for 91.7% of the emission intensity at the sub-divisional work level. Among the sub-items of tunnel section works, segment prefabrication and transportation make the largest contribution, followed by main tunnel excavation, while tunnel portal ring works contribute the least. (4) The established emission intensity indicator system can support route scheme comparison, carbon source identification during the construction stage, and the development of industry-level emission intensity benchmarks.

Research purposes: Under the background of the "dual carbon" strategy, the problems of resource waste and environmental impact in railway engineering construction have become increasingly prominent, and the comprehensive resource utilization level has become an important indicator for evaluating green construction performance. Existing studies on green construction mainly focus on energy conservation and environmental protection, while insufficient attention has been paid to the coordinated utilization of water, materials, land, energy and human resources throughout the whole railway construction process. In particular, a systematic evaluation index system and method suited to the characteristics of railway engineering are still lacking.
Research conclusions: (1) An evaluation index system for the comprehensive resource utilization of railway construction is established from five dimensions, namely water, materials, land, energy and human resources, including 5 first-level indicators and 15 second-level indicators. (2) A fuzzy matter-element model based on combined weighting is proposed, and a scale-based entropy weight method is introduced to improve the engineering applicability of the model under data-limited conditions. (3) The empirical results of the LQTJ-1 section of the LN Railway show that the overall project grade is S₄, indicating a medium green level, with relatively good performance in material and water resource utilization, while energy, land and human resource utilization still need improvement. (4) The evaluation results are highly consistent with the actual field conditions and can effectively reveal differences and key influencing factors in resource utilization during the construction stage. (5) The findings can provide a theoretical basis and methodological support for evaluating the comprehensive resource utilization of green construction in railway engineering and optimizing resource management during the construction stage.

Research purposes: With the advancement of China's Belt and Road transport infrastructure projects, some Western countries disregard facts to discredit such initiatives by citing excuses such as "debt traps" and "challenges to the international order", attempting to disrupt relevant cooperation processes. Against this backdrop, an empirical test on the positive promotion effect of connectivity projects on the economic development of countries along the routes holds important academic value and policy significance. This paper adopts the synthetic control method model to evaluate the impact mechanism and intensity of the opening and operation of the China-Laos Railway on Laos' export-oriented economic development, providing solid case evidence for the regional economic promotion effect of the Belt and Road Initiative.
Research conclusions: (1) The synthetic control method model verifies that the China-Laos Railway has improved the accessibility of freight and passenger transportation in Laos, thereby boosting the production efficiency of Laos' export goods and services, with the facilitating effect becoming more significant over time. (2) The placebo test based on mean squared prediction error further confirms that among six Southeast Asian countries, namely Laos, Cambodia, Myanmar, Bangladesh, Vietnam and Thailand, the change in Laos' actual export-oriented economy before and after the opening of the China-Laos Railway ranks first, indicating the significant promotion effect of this cross-border railway on developing countries in Southeast Asia. (3) This conclusion can provide methodological and implementation pathway for studying the economic and social impacts of similar cross-border railway investment and construction on countries along the routes.