Research purposes: The Jiujiawan landslide is a rare landslide geological disaster that caused damage and suspension of high-speed railway since the construction of high-speed railway in China, and it will surely have a far-reaching impact on the geological alignment selection in the construction of high-speed railway. The study of the characteristics and causes of this landslide will help the technical workers have a deep understanding of the high slopes along the high-speed railway and their potential risks, and provide valuable experience for the prevention and control of similar geological disasters in the future.
Research conclusions: (1) Jiujiawan landslide is a new landslide formed by the instability of natural slope, and it is a natural disaster that occurs suddenly under the combined effect of extreme heavy rainfall and man-made activities on high steep slopes of mudstone sandwiched with gypsum rock. (2) The long-term leakage of the irrigation canal at the foot of the slope is the main reason why the landslide was able to continue to slide forward on the river terrace for three days and travel more than a hundred meters after being sheared out from the foot of the slope and ultimately caused damages to the bridges of Lanzhou-Xinjiang High-speed Railway. (3) The research results can be applied to the selection of railway schemes in mountainous areas to avoid the risk of the line being subjected to landslides and geological hazards.

Research purposes: Dolomite sanding is a special karst phenomenon, which is highly disaster-causing in water-rich environments. To reveal the cause of disaster caused by tunnel surge in water-rich sanded dolomite stratum, the control measures are provided. Based on the Jixin Tunnel from the Emei to Miyi section of the Chengdu-Kunming Railway capacity expansion project, this paper investigates the tunnel surge accident, analyzes the formation causes of white cloud sand by combining regional geology, indoor microscopic observation methods, and physical and mechanical tests, summarizes the disaster mode and causes of sanded dolomite, and puts forward control measures.
Research conclusions: (1) The regional dolomite sanding mechanism is a permeation-dissolution decomposition mechanical disintegration type, and the water-rich sanding sacs distributed in the formation are the disaster source of tunnel gushing. (2) Sanded dolomite is dominated by fine particles, poor uniformity, and significantly attenuated shear strength in water. Tunnel surge failure modes can be divided into penetration-type surge, progressive surge, and intermittent surge. (3) The disaster source identification, disaster source water pressure reduction, disaster source reinforcement, low disturbance excavation construction control countermeasures are proposed.(4) The research results can be applied to the control of tunnel water outburst disasters in sanded dolomite formation.

Research purposes: The Chongqing to Guiyang corridor is the backbone section of the Baotou-Haikou and Lanzhou-Guangzhou high-speed rail corridors, as well as the railway corridor of New International Land-sea Trade Corridor in western China. Currently, it consists of the Chuanqian Line and the Yugui Line, facing issues such as capacity constraints and low transportation quality. Therefore, it is necessary to conduct a systematic study on diversion and alternative construction schemes.
Research conclusions: (1) Combining road network planning and project positioning, this paper predicts the annual traffic volume of the corridor, and analyzes that the diversion schemes for passenger and freight transportation face problems such as insufficient transportation capacity on related routes, long detour distances, and low transportation quality, making them all infeasible. Therefore, new railway lines need to be constructed. (2) The construction schemes propose three options: adding a second line to Chuanqian, maintaining the status quo for Yugui and building a new passenger and freight line, maintaining the status quo for Chuanqian and Yugui while constructing a new high-speed railway, and maintaining the status quo for Chuanqian and Yugui while building a new high-speed railway. The final recommendation is to construct a new high-speed railway that meets planning policy requirements, transportation quality, and economic benefits. (3) The research ideas and methods can provide reference and inspiration for similar projects.

Research purposes: The Quaternary cover layer in the Chengdu area is thick, overlying the red soft rock strata, with a variety of rock and soil types. The unique geological environment has given rise to numerous geotechnical engineering problems, which have constrained the planning and construction of Chengdu rail transit. Through a series of geotechnical engineering practices in Chengdu rail transit construction, this paper systematically analyzes the geological characteristics and causes of various problems and proposes targeted geotechnical investigations of key points and corresponding prevention and control measures.
Research conclusions: (1) The Chengdu rail transit is mainly located in the central part of the Sichuan Basin, which belongs to the Minjiang River watershed. Its geological structures are mainly box-shaped Longquan Mountain anticline, and the basic seismic intensity is Grade Ⅶ. (2) The Chengdu Plain is widely distributed with thick Quaternary Holocene System (Q₄) and Pleistocene System (Q₃) clay, pebbles, and sand layers, while the cover layers on the hilly and low mountain areas are thinner. The underlying bedrock is the Cretaceous System (K) and Jurassic System (J) red lacustrine sedimentary mudstone, sandstone, etc., with thin layers of gypsum and calcareous halite commonly found in the mudstone. (3) The study area has diverse rock and soil types, and the Chengdu rail transit construction faces large-grained high-strength floating pebbles, lenticular sand layers, Ya'an gravel layers, gypsum-containing formations, shallow gas, red mudstone, composite formations, and hydrogeological problems. The paper provides a detailed explanation of the engineering geological characteristics, geotechnical investigations key points, and control measures for each problem. (4) The research results have reference and guidance significance for the construction of the fifth phase of the Chengdu rail transit and the second phase of the Chengdu suburban railway network.

Research purposes: The use of ballastless track is the development trend of heavy-haul railway, and the structural design parameters are the key to carry out the design of ballastless track on the bridge of heavy-haul railway. The system coupled dynamic analysis model of vehicle-track-bridge was established in this paper, and the influence of rail type, track slab width and track slab thickness on the system dynamic characteristics were analyzed. The comprehensive evaluation was evaluated by analytic hierarchy method, and the design parameters of the single layer long sleeper embedded ballastless track were proposed.
Research conclusions: (1) Compared with 60 kg/m rail, the vertical vibration acceleration of vehicle and wheel-rail vertical force increase when 75 kg/m rail is used, and the displacement and force of track structure decrease. (2) With the increase of track slab width and thickness, the track structure vertical displacement increase, and the vibration acceleration of vehicle, wheel-rail vertical force, rate of wheel load reduction, vibration acceleration of bridge, fastener system reaction force and the contact stress between track slab and bridge decrease. (3) The dynamic comprehensive evaluation results of ballastless track decrease with the increase of the width and thickness of track slab. (4) Combined with the dynamic responses and engineering investment, it is suggested that the rail type is 60 kg/m rail, track slab width is 3.0 m and track slab thickness is 0.275 m used for the single layer long sleeper embedded ballastless track on the bridge of heavy-haul railway. (5) The research results can provide reference for structural design parameter values of single layer long sleeper embedded ballastless track on the bridge.

Research purposes: Elastic modulus is a key parameter to analyze the mechanical properties of concrete structures. In the design of prestressed concrete structures, the elastic modulus of concrete is usually directly used to simplify the calculation, but this method ignores the influence of prestressed reinforcement and ordinary reinforcement. The purpose of this study is to explore the actual influence of prestressed reinforcement and ordinary reinforcement on the elastic modulus of prestressed concrete beams through theoretical analysis and experimental verification, and to propose an analytical formula for the elastic modulus of beams based on the principle of equal equivalent stiffness. ANSYS Workbench software is used to simulate the elastic modulus of the beam under different reinforcement conditions, and the accuracy and reliability of the model are verified by experiments.
Research conclusions: (1) The reinforcement ratio of prestressed reinforcement and ordinary reinforcement has a significant effect on the elastic modulus of prestressed concrete beams, and there is a linear relationship between them. (2) With the increase of reinforcement ratio, the elastic modulus of the beam is obviously improved. When the reinforcement ratio is 3%, the elastic modulus of the beam is 27.3% higher than that of the concrete. When the reinforcement ratio is 5%, it is increased by 44.3%. (3) The research results can be applied to the design optimization of prestressed concrete structures. Considering the influence of reinforcement on the elastic modulus, it can significantly reduce the error in the structural calculation and improve the safety and economy of the project.

Research purposes: The suburban railway is an important mode of transportation to realize the integration of urban and rural areas, and its planning and construction are being vigorously promoted. However, at present, the interconnection relationship between suburban railways and various levels of rail transit is mostly analyzed at a single node, without stratified research from the perspective of the network level. Therefore, guided by the relevant planning of Shanghai and based on the passenger flow, based on the basic network pattern of Shanghai rail transit, this paper studies the interconnection relationship between Shanghai regional railway and national railway, near Shanghai regional line and municipal network from a hierarchical perspective, in order to provide a criterion for the interconnection relationship of Shanghai suburban railway.
Research conclusions: (1) With the national railway trunk line, it is recommended that the Shanghai airport link line, the East-west link line and the national railway cross-line operation. (2) Based on the planning guidance and the form of ring + ray, it is proposed that the ray should be operated across the line with the near Shanghai regional railway, and the transfer form can be adopted between the ray and the ring line. (3) In Shanghai, the suburban line network is mostly distributed in a chessboard shape. The vertical and horizontal lines and the suburban line extending into the main urban area should be operated across the line. The horizontal line and the vertical line should be comprehensively compared and selected for passenger flow, travel time, engineering investment and other factors. Under the condition that it does not have a great impact on the line station plan, it is suggested that the horizontal line and the vertical line should be operated across the line, and the ' L ' line should be used to make up for the parallel line defects, and the internal layout is equivalent to the radial line. (4) The research results can provide a reference for the selection of suburban railway interconnection relationship.

Research purposes: This paper uses the analytic hierarchy process (AHP) to study the evaluation and selection of railway hub schemes for newly built lines. By introducing concepts such as weight, membership degree, and consistency, based on fuzzy mathematical concepts, the relative superiority degree of each scheme is determined under evaluation criteria such as overall layout, transport indicators,technical indicators, and operational indicators. With the goal of maximizing the total relative superiority degree of each scheme, a hierarchical structure model is constructed. The scores of each scheme are quantitatively calculated using Matlab programming, and the optimal scheme is determined through comprehensive scores.
Research conclusions: (1) By introducing the concept of systems engineering and transforming qualitative analysis methods into quantitative calculations for comprehensive comparison of all factors, the traditional list evaluation method can effectively overcome the disadvantage of being greatly influenced by subjective factors.(2) Taking the introduction of Nantong-Suzhou-Jiaxing-Ningbo high speed railway into Jiaxing railway hub as an example, the AHP analytic hierarchy process was used to analyze and verify various schemes, and the results were consistent with traditional evaluation schemes, indicating that this evaluation method has good applicability.(3) The research results have reference value for decision-making on the introduction of railway hub schemes for future planning of new lines.

Research purposes: China has maturely applied and formed a technical system for overhead contact systems and equipment at 350 km/h and below, but still lacks relevant technical standards and engineering applications at operating speeds of 400 km/h. It is urgent to study the feasibility of the existing overhead contact system at a higher operating speed of 400 km/h to promote the implementation of the CR450 scientific and technological innovation project. This paper combined with the existing typical overhead contact system types in China, through the dynamic coupling simulation of the bow and catenary and the analysis of high-speed comprehensive test data, the tension, facility section, and equipment of the existing overhead contact system were studied to be more adaptable at a higher operating speed of 400 km/h. It is proposed that the existing overhead contact system cannot meet the operating requirements of a higher speed of 400 km/h, and the next research ideas and directions are proposed.
Research conclusions: (1) The existing overhead contact system has deteriorated the current-collecting quality of the catenary at a speed of 400 km/h. When the EMU is running with a single pantograph, it is close to the standard limit. When the EMU is running with double pantographs, it cannot adapt the requirements of higher speeds. (2) When the existing overhead line system runs at a speed of 400 km/h, the spatial dynamic displacement of the conductors, positioning, droppers, elastic suspension cables, electrical connections, etc. increases, and the conductors and components are prone to collision and wear, increasing safety risks. (3) The existing overhead contact system has aggravated equipment vibration fatigue when operating at a speed of 400 km/h. Although it can meet the load strength requirements, the durability and stability of the system and equipment are reduced, and the service life is greatly shortened. (4) The research results can provide a reference for the construction operation and maintenance of high-speed railway projects in the field of rail transportation.

Research purposes: Foreign object intrusion is one of the most serious threats faced by railways, and in recent years, train derailments and casualties have occurred repeatedly. At present, foreign object intrusion mainly relies on personnel monitoring, but personnel cannot monitor and warn in real time, and there are many blind spots. In order to achieve real-time intelligent monitoring of foreign object intrusion, the monitoring technology of U-Net siamese network model was studied, and sample libraries of different types of foreign objects were established. By comparing and analyzing with traditional methods, the effectiveness of our method was verified, laying the foundation for the engineering application.
Research conclusions: (1) The proposed U-Net siamese network model constructed by ResNet-101 integrates semantic information of different scales, greatly reducing the problem of missed detection of target objects, and has obvious advantages compared to traditional algorithms. (2) The U-Net siamese network model has generalization ability in recognizing different types of foreign objects, with high recognition rates for trains, personnel, tree branches, stones, and light floating objects. (3) The accuracy and recall of U-Net siamese network model reached 0.95 and 0.96, respectively, with false detection and missed detection rates of 0.05 and 0.04, meeting the requirements of railway monitoring. (4) The research results can provide a scientific method for intelligent recognition of railway foreign object intrusion, which can serve as an important supplement to manual inspection and has great promotion value.

Research purposes: During the construction of railway karst tunnels, when problems such as water gushing, mud bursting, and huge cavities are encountered, the design changes will be carried out based on supplementary investigation, and the operation safety can generally be guaranteed after renovation. However, some karst hydrogeological problems of railway tunnels that are not exposed during the construction period may form diseases that affect the operation's safety under extreme rainfall and other conditions after opening for operation. Hydrogeological diseases during the operation of typical railway karst tunnels mainly include track uplift, sidewall damage, mud gushing and sand gushing, and large water inflow. It is necessary to summarize these diseases in the operation period and analyze their causes, to provide a reference for avoiding similar diseases in the railway operation period.
Research conclusions: (1) The construction excavation blocking the underground river channel at the bottom of the tunnel reduces the drainage capacity of karst water. After extreme heavy rainfall, the inflow of water on the upstream side increases, which can lead to an increase in groundwater level and thus increase the water pressure acting on the bottom of the tunnel. When the bottom of the tunnel cannot resist the action of water pressure, a rail lift may occur. (2) During the operation stage, the reasons for the cracks on the side wall of the tunnel are mostly related to the open karst caves on the side wall. The lack of understanding of the rapid rise of karst water pressure in the cavity around the tunnel under extreme rainstorms and the lack of targeted water diversion and drainage measures may lead to cracks in the secondary lining after extreme rainfall. (3) During the operation of the tunnel, there is a surge of mud and sand. Due to heavy rainfall, the groundwater level around the tunnel rises and the water pressure increases, causing the mud and sand in the surrounding dissolution joints and grooves to be "pressed" into the tunnel. When mud and sand surges occur during construction and operation, the treatment measures should mainly focus on diversion and drainage. (4) The necessity of adding a drainage tunnel during the construction process should be fully considered, taking into account the water inflow situation under extreme weather conditions and the operational interference caused by a large amount of water inflow. (5) The research results of the paper have reference value for guiding the survey and design of tunnel engineering in karst water development areas.

Research purposes: Ventilation system is very important in the disaster prevention and rescue system of railway tunnels, and ventilation standards significantly affect the safety and investment of rail project. The effects of smoke concentration control and project economy at different wind speeds cases on a typical emergency rescue station between continuous tunnel portals were calculated, and the results can help to renew the ventilation standards.
Research conclusions: (1) The distribution of smoke concentration along the passenger evacuation route is influenced by multiple coupled factors, including the location of the fire source, valley winds, and the wind speed inside the tunnel. (2) When the burning train carriage is 10 meters away from the tunnel portal and there is a valley wind of 5 m/s, a tunnel wind speed of 0.5 m/s can ensure that the intrusion of smoke into the tunnel does not exceed 20 meters. (3) The wind speed standard has obvious influence on the fan configuration of disaster prevention ventilation system, and lowering the wind speed standard to 0.5 ~1.0 m/s can reduce the total number of fans by 1/3~1/2 compared to the current regulatory standards. (4) Considering safety and cost factors, it is suggested to reduce the wind speed standard to 0.5 ~1.0 m/s . (5) The research results can provide reference for the formulation of ventilation standards and ventilation system design of emergency rescue station between continuous tunnel portals。

Research purposes: With the rapid development of railway transportation and the acceleration of nationwide urbanization, railway freight stations, as core infrastructure of the transportation and logistics system, play a crucial role in reducing overall logistics costs. This paper addresses current challenges faced by railway freight stations, such as outdated facilities, industrial mismatches, and limited urban integration, and explores new pathways for their transformation into modern logistics hubs while promoting integrated development with cities and industries. The findings are expected to contribute to the high-quality development of China’s railway freight sector.
Research conclusions: (1) The theory of "Station-Industry-City" integrated development is innovatively proposed, with railway freight stations as the core, included its development connotation, path, and stages. (2) The integrated development strategy of "Station-Industry-City" is summarized from five dimensions: functional integration, transportation integration, industrial integration, spatial integration, and data integration. (3) The effectiveness of the theory is validated through an empirical analysis of the Chongqing Tuanjie Village Container Center Station. (4) The research results can provide theoretical guidance and practical references for the planning and design of new large-scale railway freight stations and logistics bases, as well as the renovation of existing freight facilities.

Research purposes: The Wuhan-Yichang section of the Shanghai-Chongqing-Chengdu Railway, as a key section of China's "Eight Verticals and Eight Horizontals" high-speed railway network, is an important intercity channel between the Wuhan urban agglomeration and the Yichang-Jingzhou-Jingmen urban agglomeration. Through the research, it is planned to achieve the scientific introduction of the Shanghai-Chongqing-Chengdu Railway into the Jingmen region and rationally determine the route alignment and station layout scheme of the introduction of the Shanghai-Chongqing-Chengdu Railway into the Jingmen region.
Research conclusions: (1) Based on the current situation of railways in Jingmen area, coordinated urban planning and the direction of Shanghai-Chongqing-Chengdu Railway and Xiangyang-Jingmen-Jingzhou Railway, combined with the pre measurement of passenger train pairs in Jingmen area, five schemes for introducing railway routes into Jingmen area are proposed. (2) By analyzing the route direction and length, engineering investment, station location, transportation organization, adaptability to urban planning, difficulty of project implementation, and social impact, a reasonable layout of the route plan is selected. (3) The introduction plan to the north of the city has the advantages of a straight route, good station conditions, flexible operation, low investment, and easy implementation. It also helps to enhance the radiation and driving ability of Jingmen to surrounding cities. Therefore, it is recommended. (4) The research results can provide reference and guidance for the planning and site selection of similar new railway hubs.

Research purposes: In response to the requirement of signal system switching between the CTCS signal system and the CBTC signal system for the cross-line operation of trains in suburban railways, the technical routes of different signal system switching are analyzed and studied in terms of the advancement of technical routes, conformity of specifications and so on, the switching locations of different signal system switching are compared and analyzed in terms of safety of switching locations, division of dispatching boundaries for different type of railways and so on, and the applicability of each technical scheme of different signal system switching for cross-line operation to the construction of different projects is systematically clarified.
Research conclusions: (1) The technical route that the systematic structure and communication interface of the CTCS signal system and CBTC signal system are completely independent and should be adopted in the project that will be constructed soon, such as the project of running suburban trains in the Beijing Railway Hub Northeast Ring Railway. (2) The technical route that the CTCS signal system is independent, and the CBTC signal system adds new conversion equipment using the existing communication interface of the CTCS signal system and CBTC signal system, and the technical route that systematic structure of the CTCS signal system and CBTC signal system remains unchanged and system equipment of CTCS signal system and CBTC signal system increases the communication interface can be applied in construction projects after completing the preconditions of project implementation such as certification and licensing and so on. (3) The technical route of systematic structure and communication interface of the CTCS signal system and CBTC signal system are completely integrated is the development direction of the signal system, which can be applied in long-term projects. (4) The stopping at junction stations of different types of railways should be selected to complete the different signal system switching for cross-line operation in the project. (5) The research results proposed in this paper can provide a reference for the design and construction of other suburban railway projects.

Research purposes: In order to investigate the changes in physical and mechanical properties and the expansion and development of internal cracks in the compression state of prefabricated fissured rocks with different inclination angles, this paper constructed a two-dimensional uniaxial compression test model using particle flow software. In order to simulate the uniaxial compression test of fissured rocks with different inclination angles, and to analyze the influence of fissure inclination angle on the compressive strength and crack expansion characteristics of rocks, a comparison was made of the simulation results of fissured rocks with different inclination angles.
Research conclusions: (1) The peak strength and cumulative number of microcracks of the intact rock specimens are the largest. As the fissure inclination increases, the peak uniaxial strength and cumulative number of microcracks of the specimens initially decrease and then increase. The peak uniaxial strength and cumulative number of microcracks of the specimens are the smallest at a fissure inclination angle of 30°. (2) The final damage mode of the specimens with different slit inclination angles is predominantly shear damage, accompanied by local tensile damage. However, the slit inevitably results in alterations to the crack extension pattern when the specimens are damaged, with the slit inclination angle of 60° representing a critical boundary. (3) The crack expansion process of specimens with different crack inclination angles can be divided into three stages: the initial stage, the slow crack expansion stage, and the rapid crack expansion stage. The earliest microcracks appeared in the uniaxial compression simulation of specimens with a 30° crack inclination angle. (4) The crack expansion characteristics are helpful for engineers to analyze the failure mechanism of rock mass engineering, and formulate the corresponding support and stability maintenance measures accordingly. The research findings have broad application prospects for the maintenance of engineering safety.

Research purposes: The Zhongxiang Hanjiang Bridge is a key controlling project of the newly constructed Shanghai-Chongqing-Chengdu High-speed Railway section from Wuhan to Yichang, designed as a (60+78+270+78+60)m double-tower, double-plane cable-stayed bridge to meet navigation and flood control requirements. It represents the largest span concrete deck cable-stayed bridge for high-speed railways with a speed of 350 km/h on a ballastless track in China. This paper conducts an in-depth study on the design of long-span prestressed concrete cable-stayed bridges based on the structural characteristics of this bridge, providing references for similar projects in the future.
Research conclusions: (1) The main girder adopts a prestressed concrete cross-section. Through comprehensive research on aspects such as the bridge's final state after construction, girder height, and tower height, a reasonable structural design scheme has been selected. The post-construction creep of the main girder is controlled to 22.5 mm, and the ballastless track exhibits good compatibility with the bridge. (2) The Zhongxiang Hanjiang Bridge demonstrates excellent static and dynamic characteristics, with favorable load-bearing performance and high safety reliability. (3) Using the 60 m chord midpoint chord measurement method, the calculated design value for static long-wave irregularities of the track is 4.9 mm, meeting the track acceptance standards. (4) An integrated bridge-rail health monitoring system is installed to promptly understand the response characteristics and operational status of the bridge and track structure under various loading conditions. (5) The successful implementation of this bridge marks a breakthrough in the application of large-span prestressed concrete girders on ballastless track bridges designed for speeds of 350 km/h.

Research purposes: The railway channel between the neighboring provincial capitals has gradually formed and presented a multi-line pattern. With the rapid development of regional social economy, the current situation of the channel has been difficult to meet the needs of channel transportation, and it is necessary to accelerate the construction and implementation of channel planning routes. Passgage planning route construction scheme selection is particularly important, not only to meet the rapid growth of the transportation needs of the channel, but also to achieve the maximum transport quality and transport benefits of the channel. Based on the Shanghai-Hangzhou railway channel and the Chongqing-Guizhou railway channel, this paper studies the route construction scheme of multi-line railway channel planning.
Research conclusions: (1) Railway passage planning should be adapted to the needs of regional social and economic development. (2) In-depth analysis of the status quo and existing problems of the railway channel, combined with the upper planning of the channel line, and scientific and reasonable determination of the construction plan of the planned line in the channel. (3) The railway channel planning line construction scheme should be coordinated with the overall standard of the channel to maximize the transport quality and transport efficiency of the channel. (4) This study can provide a reference for the selection of similar railway passage planning route construction schemes.

Research purposes: With the continuous increase in the operating speed of urban rail transit, the performance of the existing rigid catenary system under high-speed conditions of 250 km/h has not been fully studied. To meet the growing demand for passenger flow and ensure the stability and reliability of high-speed train operations, it is imperative to optimize the design of the rigid catenary system for 250 km/h speeds. This paper aims to use the finite element simulation method, investigate the influence of different structural parameters on the dynamic performance of the pantograph-catenary system, and propose a design scheme for the rigid catenary system suitable for 250 km/h speeds, providing theoretical support and engineering guidance for the power supply system of high-speed urban rail transit.
Research conclusions: (1) Through simulation analysis, the basic structural parameters of the rigid catenary at 250 km/h speed were determined: a span of 6.5 m, anchor stiffness of 68 600 N/m, and a 200% increase in the longitudinal moment of inertia of the busbar can significantly improve the dynamic performance of the pantograph-catenary system. (2) The transition structure parameters were optimized: the anchor stiffness of the fracture-type anchor section joint was set to 200 000 N/m with a span of 2 m, and the anchor stiffness of the through-type anchor section joint was set to 200 000 N/m with a span of 4.5 m. Reducing the weight of expansion elements appropriately can effectively enhance the dynamic performance of the anchor section joint. (3) By extending the length of the rigid-flexible transition busbar to 5.4 m and adopting gradient-varying anchor stiffness, the contact force requirements for the pantograph passing through the rigid-flexible transition section at 250 km/h can be met. (4) The influence of geometric deviations at the anchor section joint on the contact force was studied, and it is recommended to control the geometric deviation within ≤5 mm to ensure the stability of the pantograph-catenary contact performance. (5) The research results of this paper can provide a theoretical basis for the design of rigid catenary systems at 250 km/h and higher speeds, applicable to the optimization of power supply systems in high-speed urban rail transit, underground railways, and other related fields.

Research purposes: With the development of underground space utilization and underground rail transit, it is common to encounter deep excavations in urban areas that are adjacent to or underpass existing railways and other critical structures. However, a systematic understanding of related construction technologies remains lacking. Based on a highway underpass railway overpass project in Wenzhou, this study focuses on the construction safety of deep excavations close to railway overpasses, aiming to develop a scientific methodology for low-disturbance construction of deep excavation projects under existing railway lines.
Research conclusions: (1) A reliable support scheme of "double-row piles + steel/concrete internal bracing" was proposed, and a refined, whole-process numerical model for deep excavation adjacent to railway overpasses was established. (2) Based on this model, the deformation characteristics and stability of the excavation and bridge piers during the excavation process were systematically studied, and the "deflection effect" of pier inclination was proposed according to the displacement characteristics. (3) The validity of the numerical model was confirmed by comparison with monitoring results, and a technical scheme for "low disturbance and rapid construction" of deep excavation adjacent to important buildings was summarized. (4) The research findings can provide a reference for the design of deep excavations close to railway overpasses.

Research purposes: Accurate identification of tunnel lining surface cracks is essential for intelligent maintenance of railway infrastructure. To address the challenges of low accuracy and limited reliability in crack detection under complex railway tunnel conditions, this paper proposes a reliable and intelligent crack recognition method enhanced by image structural features and attention mechanisms, to support precise and rapid detection of crack-related defects in large-scale operating railway tunnels.
Research conclusions: (1)The reliable tunnel lining crack detection method based on the U-Net semantic segmentation architecture is developed.(2)Extensive experiments conducted on the large-scale public CrackSeg9K dataset demonstrate that the proposed method significantly outperforms existing crack detection approaches in terms of accuracy.(3)The designed feature fusion strategy, which integrates multi-structural image features and attention enhancement, effectively improves the accuracy and completeness of crack detection results.(4)The proposed method shows higher accuracy in detecting fine cracks and exhibits better cross-scene robustness, offering practical value for engineering applications in tunnel crack defect detection.

Research purposes: The quality inspection of railway tunnel linings is crucial for tunnel integrity and railway operational safety. Currently, the detection of tunnel lining defects primarily relies on the manual interpretation of radar images, and the process is inefficient and subject to significant subjective bias. To enhance the efficiency of defect detection, this study proposes an intelligent detection technology based on convolutional neural networks for tunnel lining defect images. Furthermore, to improve the applicability of this technology in practical engineering, we focus on developing a more lightweight tunnel lining defect detection technique.
Research conclusions: (1) Analysis of radar images of tunnel lining defects revealed significant background interference and a high dependence on prior knowledge of defects, resulting in low identification efficiency. (2) A novel method for determining insufficient lining thickness was developed. This method can filter most background noise and effectively mark thickness deficiencies. (3) A new lightweight network model for detecting tunnel lining defects was constructed. Comparative experiments demonstrated that the model accurately detects voids and rebar deficiencies, achieving high detection precision with excellent lightweight performance. (4) Field trials demonstrated the practical engineering applicability of this technology in railway tunnel quality inspections, providing an effective alternative to manual identification methods for detecting tunnel lining defects.

Research purposes: The Xijiang Super Major Bridge of Zhuhai-Zhaoqing High-speed Railway is a cable-stayed bridge with three towers and a main span of 2×435 m. To reduce the bending moment of the middle tower, reinforcing cables have been set up between the top of the middle tower and the side tower. To reduce the diameter of the reinforcing cables and consider its replaceability, the reinforcing cables is in the form of parallel double cables. Based on the experimental results of the aerodynamic characteristics of the downstream cylinder in the double cylinder system, the study and analysis of the characteristics of wake-induced vibration of the downstream strengthened cable under wind action in different inflow directions are carried out through numerical calculation methods, and appropriate vibration suppression measures are proposed.
Research conclusions: (1) Numerical calculation method was used to analyze the wake-induced vibration of parallel reinforced cables with a spacing ratio of L/D=3.17 (L is the distance between the center of the reinforced cable and D is the cable diameter). When the central connecting line between parallel cables is at a certain angle to the incoming flow direction, the wake-induced vibration along a circular trajectory will be caused for the uneven spatial distribution of the aerodynamic force of the downstream cable. (2) Within the range of 1.5% damping ratio, simply increasing the damping ratio of the cable cannot suppress the occurrence of wake-induced vibration, and has limited effect on reducing the amplitude of wake-induced vibration. By setting auxiliary cables and transverse connecting rods to increase the stiffness or natural frequency of the cables, the occurrence of wake-induced vibration can be effectively suppressed. (3) This study can provide reference and inspiration for the design of cable-stayed bridges using double row cable-stayed or reinforced cable.

Research purposes: With the continuous improvement and rapid construction of China's railway network, the impact of railway engineering on the ecological environment along the routes has become increasingly evident. Particularly in ecologically fragile desert regions, the issue of environmental pollution during railway construction is more pronounced. Although green construction practices have been widely adopted in railway development, there is still a lack of systematic environmental impact assessment frameworks and methodologies, making it difficult to accurately evaluate the actual environmental impact of construction activities and to provide a scientific basis for environmental management decisions. In light of this, this paper aims to establish a scientifically sound environmental pollution evaluation index system for green railway construction in desert areas, comprehensively reflecting the impact of construction activities on water environment, atmospheric environment, acoustic environment, solid waste disposal, and ecosystems. Furthermore, it seeks to develop a quantitative environmental impact assessment model to achieve an objective evaluation of the environmental impact of green railway construction. Lastly, through empirical research, the paper intends to validate the effectiveness of the evaluation system, providing theoretical support and practical guidance for formulating targeted environmental protection measures.
Research conclusions: (1) This paper constructs an environmental pollution evaluation index system for desert railway green construction, comprising 5 first-level indicators and 16 second-level indicators. It innovatively combines the entropy weight method with the fuzzy comprehensive evaluation method to establish a quantitative environmental impact assessment model. Using this model, the paper evaluates the environmental pollution impact of green construction on a section of the Golmud-Korla Railway. The environmental pollution evaluation grade for this section is "weak", indicating a relatively minor environmental impact. (2) Ecological disruption is the primary factor causing environmental pollution in railway green construction, and protective measures should be implemented during construction to effectively control it. (3) This evaluation index system can provide a direction for further improvement in the prevention and control of environmental pollution in railway green construction, offering reference value for optimizing construction measures and improving pollution management methods. It holds reference value for reducing environmental pollution and achieving high-quality green railway construction.

Research purposes: To ensure the safety of the construction and operation period of the tunnel in tuff strata, on-site sampling was employed for in-door testing to study the engineering characteristics of tuff strata. Combined with the disaster situation during the construction period of the tuff section in the Liren tunnel of the ongoing construction of the Xi’ning-Chengdu Railway, engineering countermeasures were proposed and their effects were verified on site. It is beneficial to clarify the impact of tuff strata on tunnels and improve tunnel design theory.
Research conclusions: (1) Weakly weathered hard tuff has a tuffaceous sand-like structure, with a mineral composition mainly composed of sand-like minerals. It has relatively good water stability and is mainly non-expansive, so no strengthening measures are needed. Strongly weathered soft tuff has a tuffaceous structure, with volcanic ash as the main mineral composition and a high content of hydrophilic minerals such as montmorillonite. It has obvious water physical properties and is mainly characterized by moderate to strong expansibility. (2) Weakly weathered hard tuff has high strength, good self-stability of tunnel face, and no corresponding section disasters on site. Strongly weathered soft tuff has relatively low strength, and it cannot even be sampled. It is an extremely soft rock, and the self-stability of the tunnel face is poor. There have been multiple instances of face collapse, initial support intrusion, sprayed concrete cracking, and detachment in corresponding sections on site. After excavation, the foundation 1~2 m of tuff collapsed and softened, and measures need to be strengthened. (3) The engineering analogy method is used to propose countermeasures for tunnel engineering in strongly weathered soft tuff. Deformation control measures include strengthening advanced support measures, arch wall radial grouting, setting buffer layers between initial support and secondary lining, etc. The safety control measures for the foundation use steel pipe piles and waterproof layers. Field tests have shown that the above engineering measures have significant control effects. (4) The results of this study can provide a reference for the design of railway tunnels in similar tuff strata.

Research purposes: The complex geometry composed of bridge abutment and cone fill has been visualized in 3D, but the structural dimensions, types of forces, live load arrangements, and load combinations of bridge abutment are diverse. Therefore, in structural calculations, it is difficult to accurately simulate and form a universal algorithm, which is a challenge for the digital transformation of bridge design. This paper establishes a mathematical model suitable for external force calculation, load combination, and abutment body inspection by summarizing and analyzing the geometric data of bridge abutments and cones, and proposes a universal calculation method for bridge abutments that spans specifications and domains.
Research conclusions: (1) Segmented construction of bridge abutment and cone fill can reproduce the geometric dimensions of the original structure and accurately calculate characteristic values such as abutment’s self-weight, soil pressure, seismic force, and overall stability. (2) The four types of bridge abutment live load layout diagrams and quantitative discriminant equations established can quickly and accurately calculate the most unfavorable position and size of any live load on the bridge abutment. (3) The proposed bridge abutment data modeling and general calculation method have been verified to have a maximum error of around 1.1%, and the calculation is fast and highly versatile. (4) The research result has been applied in the design of railway bridge abutments, and can also provide reference and guidance for the calculation of bridge abutments in highways and urban rail transit.

Research purposes: With the continuous advancement of tunnel engineering in complex geological conditions in western China, water and mud inrush during mountain tunnel construction has become increasingly frequent and severe. Among these disasters, time-lag inrush events characterized by suddenness and hysteresis pose significant challenges to construction safety due to their pronounced spatio-temporal uncertainties. This paper analyzes the formation environments and process mechanisms of recent time-lag water and mud inrush events in mountain tunnels, proposes their definitions, classifications, detection and prediction technologies, and establishes a set of reliable risk identification and prevention measures for field construction.
Research conclusions: (1) Time-lag water and mud inrush events can be classified into three categories based on spatio-temporal characteristics: water gushing-piping type, flow soil-collapse type, and composite type.(2) High-risk zones for time-lag inrushes typically exhibit disaster-prone environmental features such as surface negative topography, structural fracture zones, low-resistivity anomaly regions in geophysical surveys, and minor angles between maximum principal stresses and negative topography/structures.(3) A semi-quantitative evaluation method was developed to assess risk levels (Levels I,II,and III) and probabilities of time-lag inrush, considering factors including rock fragmentation, water outflow state, primary support conditions, and construction collapse impacts.(4) Prevention strategies should follow the principle of "prioritizing robustness over weakness and ensuring one-time pass-through". Key measures include extended detection range, long-distance pressure relief, graded reinforcement techniques, and hierarchical risk mitigation for hysteresis hazards.(5) The research results can provide references for predicting and controlling time-lag water/mud inrush in similar complex geological settings.

Research purposes: Faced with the new situation and requirements of the urgent need for renovation and reconstruction of a large number of old railway passenger stations and surrounding urban areas in our country, Xi'an Railway Station has also presented the reality problem of the disconnection between "station" and "city" and the coordination between "ancient" and "present".This paper focuses on the renovation of the Xi'an Railway Station hub area from the perspective of urban renewal, summarizing issues such as transportation network structure, urban functional formats, and cultural landscape, and proposes a renewal method for the old railway station area by combining station-city integration and catalyst renewal strategies.
Research conclusions: (1) The research method is proposed combining catalyst renewal theory and station-city integration theory to address the complex situation of updating and renovating old railway stations. (2) The urban renewal strategy is proposed for old railway stations in the hub area of Xi'an Railway Station, which integrates urban functions, transportation functions, landscape functions, and cultural features. (3) The overall research direction of "pre planning and post evaluation" is proposed for the updating and renovation of old railway station areas. The paper explores the practical solution of "integrating hub transportation and urban functional space, focusing on the inheritance and expression of cultural heritage with large heritage sites" for the stock renewal of hub areas.

Research purposes: Based on the hazards of shield residues by traditional disposal methods, this paper takes Chongqing shield residues as the research object to identify the physical and mechanical properties and microstructure of shield residues in sand and mudstone strata through indoor experiments. Then, the advantages of resource utilization of shield residues will be made clear, and resource utilization ideas will be systematically put forward.
Research conclusions: (1) The shield residues, mainly composed of moderately weathered sandstone and mudstone formations, belong to low liquid limit clay with good gradation and continuous soil particle size. It is mainly composed of minerals such as quartz, corundum, calcite, and sodium feldspar, and is weakly alkaline. (2) In sand and mudstone formations, shield residue has the advantages of uniform particle size and continuous gradation, high hardness of mineral particles, stable behavior, and weak alkalinity. And the mechanical properties and durability of recycled products can be effectively guaranteed. (3) From the view of the resource utilization of shield residue, it should be considered that the proportion of polymer in the residue improver should be increased appropriately. The particle size grade of residue can be increased, and the wear of the cutter head and cutter tool during shield tunneling can be reduced correspondingly. To ensure the stability of the foundation after backfilling, the moisture content of shield residue should be maintained at around 42%. (4) A general idea of solidification utilization and fluid utilization is proposed through hierarchical classification processing. The preliminary theoretical system for recycling shield residues is constructed. And the advantage of carbon emission reduction is made clear. (5) This paper can provide reference for the resource utilization of similar residues in the future.

Research purposes: This paper established a three-dimensional numerical analysis model of 'bedrock-cover layer-subgrade' that can consider the features of fault creep activity, analyzed the deformation characteristics of subgrade structure under the action of fault creep dislocation, and clarified the action mode and sensitivity of various chief influencing factors on subgrade deformation, such as fault movement mode, creep amount, thickness of overlying soil.
Research conclusions: (1) Different creeping modes of active faults lead to different deformation characteristics of subgrade surface and slope, in particular, the near-fault slope under the action of strike-slip shows obvious 'middle bulging'. (2) Under the action of dip-slip fault dislocation there is a critical creep amount and critical overburden thickness that make the subgrade irregularity range tend to be stable. (3) The increase of strike-slip displacement obviously aggravates the lateral displacement of the subgrade and the 'middle bulging' of a near-fault slope, while the sufficient thickness of overburden will obviously smooth the above lateral deformation. (4) Those analysis results can provide a reference for the deformation control of railway subgrade under the background of fault dislocation.

Research purposes: In the subgrade of heavy-haul railways with significant axle loads, the strength of the subgrade is particularly crucial. Enhancing the strength of heavy-haul railway subgrades is an urgent issue that needs to be addressed in the field of engineering. To explore the improvement of the performance of heavy-haul railway subgrade, and ensure the overall stability of the subgrade, it is proposed to reinforce the subgrade soil with geosynthetic materials. The dynamic characteristics of plain soil and different reinforced soils were investigated by large-scale dynamic triaxial test.
Research conclusions: (1) The geogrids and geocells can significantly reduce axial deformation of specimens, with better performance observed in geocells.The amplitude has a greater influence on axial cumulative strain than confining pressure. The pore water pressure of specimens increases with the number of load cycles, showing three stages: slow growth, rapid increase, and gradual stabilization. (2) After reinforcement treatment with geogrids or geocells, the pore water pressure decreases significantly. (3) The stress-strain hysteresis loops under various conditions exhibit similar patterns characterized by initial dilatancy followed by compaction. (4) The damping ratio varies significantly among different specimens tested. Specimens reinforced with geocells have the lowest damping ratio while those reinforced with geotextiles have the highest damping ratio. (5) The research findings provide guidance on how to improve the dynamic characteristics of coarse-grained fill materials in heavy-haul railways.

Research purposes: The human resource management system based on the competency model focuses more on individual competence compared to work activities, which facilitates better selection and cultivation of excellent employees for enterprises. This is particularly important for enterprises that are flexible and adaptable in the rapidly changing information society. This paper takes Z Group as an example to study the construction and implementation of a human resource management system based on the competency model.
Research conclusions: (1) Talent selection emphasizes high standards, not only focusing on the relevant knowledge and skills of the position, but also on the development of core competencies. (2) Establish a talent growth and learning map, strive to improve the overall quality and innovation ability of the talent team, and achieve mutual benefit between the enterprise and employees. (3) Innovate the performance evaluation management system, improve the mechanism for determining total salary, and stimulate the enthusiasm of various talents for entrepreneurship. (4) Based on the needs, adhere to targeted talent introduction, innovate talent introduction methods, and continuously improve the matching degree between the talent team and the development of the enterprise. (5) This research result can provide a method and path for large railway construction enterprises to explore the establishment of a sound and effective human resource management system, and continuously improve their core competitiveness.

Research purposes: The excavation face and tunnel top of shield tunnels have completely different failure modes during excavation in clay and sand layers. Based on the assumption of a non-vertical sliding surface, taking into account factors such as incomplete soil arching effect and principal stress deflection, this paper proposes calculation formulas for vertical soil pressure and vertical support soil pressure of circular shield tunnels in clay layers. The rationality of the theoretical model is verified through numerical examples, and sensitivity analysis is conducted on the parameters.
Research conclusions: (1) When the burial depth is shallow, the soil pressure curve approaches linear variation. (2) When the burial depth is deep, the soil arching effect causes the curve to exhibit nonlinear changes, and the soil pressure first increases and then decreases. (3) The vertical soil pressure at the top of the tunnel increases with the increase of internal friction angle, and decreases with the increase of principal stress deflection angle, sliding surface angle, and cohesive force. (4) The sensitivity relationship of each parameter is: cohesion > principal stress deflection angle > soil sliding surface angle > internal friction angle. (5) This research achievement can provide reference and guidance for improving the theoretical system of shield tunnel design and calculation.

Research purposes: With the enhancement of human engineering construction activities, the problem of deep karst collapse induced by static overloading of dense building groups should be emphasized. This paper took a project in Xuzhou, a typical city in a karst area in southern China, as a prototype, and collected overburden clay samples with a depth of 18 m on site. An independently developed experimental device was employed to simulate the damage of deep karst collapse, the influence of static overloading of dense building groups on deep karst collapse was considered, and the triggering condition of deep karst disaster was further determined.
Research conclusions: (1) When the building plot ratio reaches 3.9 (the most unfavorable working condition), the overburdened soil will collapse in different sizes of karst cavities, establishing the critical trigger boundary condition for static overloading-induced deep karst damage. (2) Meanwhile, it was revealed that the collapse mode of water-resistant overburden was holistic and gravitationally induced, and its damage mode was mainly divided into three stages, i.e., the stage of overburden soil cracking, the stage of overburden soil extension and expansion, and the stage of overburden soil collapse. (3)The research result can provide a reference basis for the prevention and control of geologic disasters in karst development areas under human engineering activities.

Research purposes: With the basic formation of the "four vertical and four horizontal" and "eight vertical and eight horizontal" railway network, traditional railway construction technology has matured, but one map for the design, construction, construction, and operation and maintenance is still at the theoretical conceptual stage. The soft power in terms of fine design, full-monitoring construction, and intelligent operation and maintenance of railways is still a shortcoming, and it is also the fundamental bottleneck restricting the construction of independent digital railway engineering and intelligent railway system in China. With the rapid development of AI intelligence in the physical world, it is also an inevitable development trend for railway engineering to become collaborative, digital, and intelligent. In view of the current shortcomings of China's railway informatization, this paper proposes the concept of railway collaborative survey, design, construction, operation and maintenance system with one map of digital assets, the main idea is that the railway follows the technical context of digital earth and digital city, and uses the 3DGIS platform as the basic framework to build digital railway engineering assets and realize the expression of twin railways in computers.
Research conclusions: (1)The two-level evolution of "macro-micro" view constructed by GIS and BIM design has the characteristics of seamless connection of informatization in the whole stage and the whole process, loose coupling of spatial layout design and structural design, and single-scale static expression to multi-scale dynamic expression. (2) The digital asset application system centered on automated modeling of 3D route selection system mainly aims to solve the problem of universal asset access and realistic and efficient expression. (3) The construction of the "macro-micro" two-level evolutionary exploration and design system will greatly promote innovation in automated design. (4) The research achievement can lay the foundation for the forward BIM design,construction, and operation of railways.

Research purposes: The terrain and geological conditions in the western mountainous areas of China are complex, with a large number of landslide-prone geological bodies. Currently, railway projects passing through landslide areas are mostly low-grade conventional speed ballasted track railways, which mainly focus on stability control and have low requirements for deformation control.Moreover, deformation repair is relatively easy. Effective subgrade structure and landslide reinforcement measures must be taken for high-speed railway embankments passing through landslide bodies to meet the requirements of subgrade stability and millimeter level deformation control. It is of great significance to reveal the stress and deformation characteristics and failure modes of subgrade reinforcement structures in landslide areas, and to propose design methods and reinforcement principles for high-speed railway embankments in landslide areas.
Research conclusions: (1)The high-speed railway subgrade in landslide areas should be stabilized and reinforced with a combination of foundation pile-slab structure and anti-sliding piles for deformation control.(2)Setting up rear anti-sliding piles has a significantly better effect on improving the stress and reducing deformation of the pile-plate structure than setting up front anti-sliding piles.(3)When the pile-plate structure is located in the anti-sliding section, the distance between the rear anti-sliding piles and the pile-plate structure should be 3~5 times the section length of the anti-sliding piles.When the pile-plate structure is located in the sliding section, the distance between the rear anti-sliding piles and the pile-plate structure should be 0.5~2 times the section length of the anti-sliding piles. (4) The cracks in the pile foundation of the pile-plate structure are mainly concentrated at the top of the pile and near the sliding surface, while the cracks in the anti-sliding pile are mainly concentrated near the sliding surface. (5) The principles and design methods for reinforcing high-speed railway embankments in landslide areas are proposed. (6) The research result can provide useful references for the construction of high-speed railways in landslide areas.

Research purposes: In order to reveal the causal mechanism of accidents in complex mountainous railway tunnel construction, a dataset comprising 652 railway tunnel construction accident cases from 2013 to 2023 was collected. The FP-growth algorithm was employed to extract 161 association rules with high support. Based on these association rules, a hypergraph was constructed to model the causation network of railway tunnel construction accidents, and its topological characteristics were analyzed.
Research conclusions: (1) The accident causation network model based on the hypergraph clearly demonstrates the many-to-many relationships between risk events and factors, providing a powerful tool for further analysis of the complex relationships between risk events and factors in railway tunnel construction. (2) Among the six major categories of risk factors, personnel safety behavior, equipment configuration and usage, material testing are important in influencing the occurrence of events. In particular, surrounding rock stability and geological structure have a more direct impact on construction safety. (3) Rock bursts, collapses, and mud and water gushing are the most prominent risk events in the construction of complex mountainous tunnels. Factors such as geological forecasting, blasting techniques, surrounding rock stability, and complex geological structures have an important influence on these three types of risk events. (4) The research can provide a reference for the cause analysis of railway tunnel construction accidents in complex mountainous areas.

Research purposes: During the tunnel excavation process, enhancing the advanced identification and comprehensive prediction of adverse geological conditions has significant engineering guiding significance. Based on macroscopic geological and hydrogeological analysis, a risk identification method for adverse geology in tunnels has been established. The risk levels are classified focusing on issues such as rock bursts under high ground stress, mud inrushes and water gushes, soft rock deformations, and high-temperature thermal hazards. The accuracy of the method is verified by taking the prediction of high-temperature thermal hazards as an example.
Research conclusions: (1) For advanced geological prediction, it is necessary to strengthen macroscopic geological and hydrogeological analysis, and pay attention to the combination of ground and tunnel interior, the combination of geophysical exploration and drilling, the combination of different geophysical exploration methods, and the combination of long-distance and short-distance predictions. The adverse geology identification method established in this paper is innovative and scientific. (2) A single prediction method is like "a blind man feeling an elephant", which can only reveal local geological conditions. Using comprehensive prediction means can deepen the overall understanding of adverse geology and reduce ambiguity. In practical applications, multiple anomalies should not be simply superimposed, and attention should be paid to the sensitivity of each method to geological problems. (3) Advanced geological prediction is an important guarantee for construction safety. Adopting effective risk identification methods helps to prevent the occurrence of various accidents and should be incorporated into the management of construction procedures. (4) This research can provide reference for the advanced identification of adverse geological conditions in tunnels and similar projects.

Research purposes: With the acceleration of urbanization and the continuous advancement of urban infrastructure construction, the traffic service level of some urban roads can no longer meet the growing demand for traffic volume. There are situations where the expansion of traffic corridors intersects with high-speed railways. The increasingly stringent requirements for railway operation safety also pose huge challenges to the decision-making of railway-related road projects. Taking the scheme comparison of Wuhan Gaoxin Sixth Road passing under the Beijing - Guangzhou High-speed Railway as an example, this paper first conducts a qualitative analysis of the two schemes, pointing out their respective advantages and disadvantages. Subsequently, considering the complexity of the influencing factors of railway-related road reconstruction and expansion projects, the analytic hierarchy process (AHP) is selected for multi-criteria decision-making analysis and comparison.
Research conclusions: (1) The selection of engineering schemes is an important part of railway-related road engineering design. When conducting the scheme selection, various influencing factors such as railway safety, traffic impact and cost need to be comprehensively considered to arrive at the optimal engineering scheme.(2) When the differences in traffic impact and cost are not significant, railway safety occupies a major weight among the factors in the scheme comparison of railway-related road reconstruction and expansion projects. (3) This paper provides an effective method for the scheme comparison of railway-related road reconstruction and expansion projects, which has practical guiding significance for the application of the analytic hierarchy process in the comparison and decision-making of railway-related reconstruction and expansion road engineering schemes.

Research purposes: The traveling safety and system vibration assessment when the train crosses a large-span flexible bridge are the key technical difficulties in the design and construction of high-speed railway bridges toward large-span and high-flexibility, and the coupled dynamics analysis of train-track-bridge is the core. Considering the longitudinal large-scale nature of large-span bridges, the overall modeling of the track structure on the bridge will bring inefficiency in modeling and computational efficiency, which makes it difficult to meet engineering needs. In this paper, based on the classical coupled vibration theory of train-track-bridge, the cyclic calculation method and substructure power iteration method are introduced to realize the coupled train-track-large-span bridge vibration analysis by moving the truncated train-track subsystem on the bridge, as well as coupling the time-varying matrix with the bridge subsystem and solving the power iteration. Numerical analysis is carried out for two key parameters in the computational model: the track truncation length and the substructure integration step.
Research conclusions: (1) When analyzing the vibration of the large-span bridge, it is recommended that the track truncation length of more than 200 m. (2) In order to take into account the high-frequency vibration of the train-track system and the efficient calculation requirements of the bridge system, it is recommended that the integration step of the train-track system is 0.000 5 s, and the bridge system integral step is 0.001 s. (3) Based on the calculation model proposed in this article, the reasonable range of values for the longitudinal section parameters of the herringbone slope of long-span bridges is studied. When the slope ≤12 ‰ and the vertical curve radius R≥20 000 m, the longitudinal section setting requirements in the specifications are met. (4) The coupled vibration analysis method proposed in this paper realizes efficient modeling and efficient calculation, which can provide theoretical and technical support for the longitudinal section research of kilometer-class large-span bridges.