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: In response to the problems caused by the collapse of red bed soft rock subgrade along the railway, such as slurry, mud, and foundation settlement, the Jurassic red bed soft rock in the central and eastern Sichuan Basin was taken as the research object. Referring to the climate and environmental background conditions of the study area, an external disturbance resistance test was carried out under dry wet cycle conditions. Through quantitative analysis of multiple indicators of the disintegration process, the disintegration characteristics of red bed soft rock under dry wet cycle effects were explored, and the differences in the disintegration of red bed soft rock in different strata were clarified. The evolution law of disintegration rate with cyclic dry wet was identified.
Research conclusions: (1) The variation pattern of the content of disintegrated particles with the increase of dry-wet cycles in the disintegration resistance test can be divided into three stages: the rapid reduction stage of coarse particles, the stable stage of intermediate particles, and the continuous increase stage of fine particles. (2) There are significant differences in the particle content and disintegration of red bed soft rocks in different regions, with the order of disintegration strength being Neijiang> Suining> Dazhou. (3) The disintegration law of red-bed soft rock shows that as the number of dry-wet cycles increases, the disintegration resistance index, disintegration ratio, and standard basic entropy decrease continuously, while the small particle index increases continuously. As the number of wet-dry cycles increases, the disintegration rate decreases continuously, the content of large particles decreases, while the content of small particles continues to increase, and the disintegration gradually reaches stability. (4) The research results can provide a reference and theoretical basis for railway route selection and disaster prevention of red-layer soft rock subgrade.

Research purposes: In northern China, concrete structures not only face freeze-thaw cycles but also suffer from abrasion caused by sediment and gravel during flood seasons, leading to significant durability degradation. Adding high-strength, high-modulus fibers can effectively improve durability. This study investigated the concrete used in a high-speed railway bridge in northern China. By incorporating calcium sulfate whisker (CSW), freeze-thaw and abrasion tests were conducted on C40 and C60 CSWC, and the effects on durability were analyzed.
Research conclusions: (1) Incorporating CSW significantly improved the freeze-thaw and mechanical properties of CSWC. (2) The optimal surface performance under freeze-thaw and abrasion occurred with 5 kg/m³ of CSW. (3) A plastic microstrain-based freeze-thaw damage model was established to predict frost resistance durability. (4) The research results can provide a theoretical basis for the improvement of concrete durability, and have guiding significance for the practical application of CSWC in cold regions of northern China.

Research purposes: The permafrost on the Qinghai-Tibet Railway is gradually degraded due to the global temperature rise, which brings many technical problems to railway safety operation and related railway construction in the plateau cold region. By collecting and analyzing the changes in temperature, precipitation, ground temperature, and frozen soil upper limit of meteorological stations along the Qinghai-Tibet Railway, the characteristics of climate and frozen soil changes along the Qinghai-Tibet Railway under the condition of temperature rise of the Qinghai-Tibet Railway are analyzed. The research results aim to provide theoretical support for the engineering maintenance and engineering construction in the plateau cold area under warming conditions.
Research conclusions: (1) In the past 20 years, the warming rate of the Qinghai-Tibet Plateau has reached 0.64 ℃/ 10 a, and the precipitation has increased at a rate of 16.8 mm/10 a. (2) The temperature along the Qinghai-Tibet Railway is influenced by altitude and dimensions, with an average temperature value of -5.9 ℃~-2.7 ℃. The annual average precipitation has shown an increasing trend from 1996 to 2022, an increase of 75~86 mm compared to 1976 to 1995. (3) The ground temperature in the permafrost region of the Qinghai-Tibet Railway in 2022 has increased by 0.06~0.21 ℃ compared to 2007, and the temperature at the north and south ends of the permafrost has increased by 0.04 ℃~0.17 ℃. The freezing index along the route ranges from 1.5 to 5.6. (4) The research results can provide theoretical support and technical reference for the construction of road projects in plateau cold areas and the disposal of existing engineering diseases.

Research purposes: The Peck formula is one of the important methods for studying tunnel surface settlement. Its prediction results are mainly affected by parameters such as settlement groove width i and formation loss rate η, and due to the strong regional characteristics of each parameter, the parameter values vary greatly in different regions. Therefore, this paper takes the double line shield tunnel in the sedimentary strata of Kunming Lake as the research object, explores the variation rules and value distribution of each parameter, and finally obtains a surface settlement prediction formula for the double line tunnel applicable to the region, filling the research gap in China.
Research conclusions: (1) Due to the influence of the right line leading, the fitting degree of the Peck formula on the left line has decreased. (2) i is directly proportional to the tunnel depth z and can be characterized by the settlement groove width coefficient k. Its correlation with the weighted compression modulus E is weak. (3) η is positively correlated with z, negatively correlated with grouting rate g, and has little regularity with E. (4) The double line tunnel surface settlement prediction formula takes the leading tunnel k₁ [0.23,0.68], η₁ [0.31%, 1.66%], and the following tunnel k₂ [0.21,0.58], η₂ [0.31%, 1.79%]. (5) The rationality of the formula was verified by the measured data of a certain line, and the predicted results were basically consistent with the actual settlement, both located between the upper and lower limits. At the same time, based on the maximum settlement of the upper limit curve, it can be roughly judged whether the predicted settlement value exceeds the engineering warning, which can provide reference for safe construction of similar tunnels.

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: 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: In the process of conducting discrete element-based simulation analysis of the interaction between shield machines and sandy cobblestones, there is a mismatch between the actual sandy cobblestone parameters and the simulation parameters of the discrete element method. To address this issue, it is necessary to conduct physical and simulation tests on the sandy cobblestones from the actual construction stratum of the Ganguan Station-Qiandaohu Street Station (referred to as Gan-Qian Section) section of Line 3 of the Shenyang Metro. By taking the angle of repose as the response value, Plackett-Burman and Box-Behnken experimental designs were carried out to calibrate the simulation parameters required for discrete element simulation analysis, providing a basis for the simulation analysis of the interaction between shield machines and sandy cobblestones.
Research conclusions: (1) Physical experiments measured the particle size distribution, the density of 1 719 kg/m³, and the accumulation angle of 38.68°. (2) Plackett-Burman experimental design, and screened out the factors that have a significant influence on the accumulation angle of sand gravel: sand gravel-sand gravel static friction coefficient, sand-gravel-sand gravel rolling friction coefficient, sandstone-shield machine rolling friction coefficient (3) Box-Behnken experimental design, establish a regression model between the accumulation angle and the significance factor, and the inverted optimal simulation parameters are: the static friction coefficient of sand pebble is 0.599, the rolling friction coefficient of sand pebble-sand pebble is 0.195, and the rolling friction coefficient of sand pebble-shield machine is 0.033. (4) The research results can be applied to the discrete element simulation analysis of shield tunneling machines.

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: In the process of importing High-speed railway ( HSR ) construction technology, the difference of chord offsets (DoCOs) method was introduced in China Railway for representing profile/alignment irregularities. Nevertheless, there are some controversies about DoCOs’ effects on track state evaluation and maintenance operation instruction, so DoCOs’ serviceability in track maintenance should be ascertained. To address the underlying mechanism of this issue, this paper starts with the correlation between DoCOs and car body acceleration and evaluates DoCOs’ reflection capability about vehicle dynamic response using correlation coefficient and normalized mutual information. Then in view of DoCOs’ state space description, discusses track deformation representing capability of DoCOs and addresses the instruction capability for maintenance operation, which employed track deformation state-space representation and observability analysis. On this basis, compares track irregularities representing the capability of mid-chord offset (MCO) and difference of chord offsets.
Research conclusions: (1) There is a weak correlation between 5 m/30 m or 150 m/300 m DoCOs and car body accelerations, and no evidence indicates that a nonlinear mapping structure exists. (2) Since the state space of 5 m/ 30 m or150 m/ 300 m DoCOs is not complete observable, it is difficult to instruct the maintenance from DoCOs. (3) MCO’s unobservable states are quite a few compared with DoCOs’ in the track deformation state-space representing, and it could be complete observable taking some supplementary observations, moreover, MCOs are strongly correlated with car body accelerations, all these characteristics are more propitious to evaluate the track states and instruct the maintenance operation. (4) These conclusions illuminate the serviceability problem of DoCOs existing in HSR track evaluation and maintenance and could present a theoretical foundation for selecting representation indices for track irregularities.

Research purposes: In order to investigate the mechanical performance of UHPC layer in the negative moment zone of small span continuous frame bridges, the crack resistance ability, rotation ability and ultimate bearing capacity of the joint were investigated by using the real bridge scaling model. Based on ABAQUS finite element software, the numerical simulation and parameter analysis of the test model were carried out to explore the effects of key parameters such as UHPC layer length, thickness and reinforcement ratio on mechanical performance of the negative moment joints of the frame bridges.
Research conclusions: (1) The UHPC layer of frame bridge joint has a high cracking stress (6.56 MPa). In the normal use stage, the UHPC layer effectively inhibits the formation and development of cracks in the negative bending moment zone, and improves the overall cracking resistance of the structure. (2) Increasing the reinforcement ratio of UHPC layer can effectively improve the flexural bearing capacity of frame bridge joints, but will reduce the cracking resistance of UHPC surface layer. (3) The crack resistance and load bearing capacity of frame bridge joint increases with the increase of UHPC layer thickness. (4) On the premise that both the UHPC layer and the UHPC-NC interface have good crack resistance, it is the most economical to set the UHPC layer between the zero points of the negative bending moment of frame bridge. (5) The research results put forward a high performance joint design method for the negative moment zone of small span continuous frame bridge, which can provide an effective reference for similar bridge design.

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: As the center of gravity of railroad construction gradually shifts to the southwest region, deep valley long-span bridges are widely used in complex and dangerous areas. Aiming at the problems of many potential risk factors and limited accuracy of traditional assessment methods for deep valley span bridges, we take a deep valley span bridge in Southwest China as the research object, establish a risk identification and optimization system based on the Delphi method (DELPHI) versus the work-risk decomposition method (WBS-RBS) and carry out the risk assessment research based on the fuzzy hierarchical analysis method (FAHP) coupled with the results of the risk matrix method (LS) to improve the accuracy and rationality of the evaluation results from both risk identification and assessment.
Research conclusions: (1) The WBS-RBS is optimized by DELPHI, which can comprehensively and accurately identify potential risk sources, and the RBS risk decomposition structure system is determined based on the optimized 206 RBM identification results. (2) Adopting three-value coupling calculation to derive the risk degree to identify the significant risk sources can avoid the influence of single-value chance on the assessment results, and identify seven major risk sources, such as equipment quality defects, personnel working without safety measures, and equipment fixing connection is not secure. (3) In addition to the seven major risk sources, in order to improve the rigor of the assessment process, the unreasonable preparation of the construction program and flooding as a single-value risk source still need to be focused on. (4) The research in this paper can provide theoretical support and methodological reference for the safety risk evaluation of deep valley long-span bridges.

Research purposes: Frequent falling blocks in high-speed rail tunnels can cause serious economic losses and even casualties. The intensification effect of high-speed train aerodynamic load in the crack may be an important reason for the crack expansion and eventually the formation of falling block. In order to prevent falling block accidents in high-speed railway tunnels and strengthen tunnel disease control, the intensification effect of aerodynamic load in lining cracks should be studied. In this study, based on Fluent software, finite volume method (FVM) and Pressure-Based solver are used to simulate the aerodynamic pressure in crack space by unsteady viscous k-ε turbulence model considering the compressibility of air. Using this model, the temporal and spatial characteristics of the aerodynamic loads of circumferential, inclined and longitudinal cracks are discussed. The spectrum characteristics of aerodynamic pressures are analyzed, and the effects of crack length, width, depth and vehicle speed on the aerodynamic loads of crack surface are analyzed.
Research conclusions: (1) The pressure wave enters the circumferential crack space instantaneously, and the pressure wave enters the inclined and longitudinal crack space procedurally. (2) The peak value of circumferential crack pressure is 5.32 times of the input pressure. The peak pressure values of inclined and longitudinal crack are only 79.5% and 64.9% of the corresponding values of circumferential crack, respectively. (3) The PSD of the aerodynamic pressure of the circumferential crack is 4.04 and 1.54 times higher than the value of longitudinal and inclined cracks on average. (4) The crack length and width have limited influence on the peak pressure of crack surface. The crack depth and the peak pressure meet the linear function relation, and the speed and the peak pressure meet the power function relation of 2.303 3. (5) The research findings can provide references for the design of high-speed rail tunnels, and the assessment and repair of cracks within the tunnels.

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: To study the vibration and noise response of steel-concrete continuous composite beam bridges under railway heavy loads, a railway steel-concrete continuous composite beam bridge with a span of (40+50+40) m on a certain passenger dedicated line was used as the engineering background to conduct on-site testing of structural vibration and noise. The valid data for 16 trains of different formations under operating conditions has been recorded, with train speeds ranging from 160 to 210 km/h. Based on the valid data, the characteristics of vibration and noise of railway composite beam bridges were analyzed and discussed. This research can provide data reference for the research and engineering application of acoustic and vibration response of railway composite structure bridges.
Research conclusions: (1)The results showed that the dominant frequency range of vehicle-induced vibration of the composite bridge was 30 to 2 000 Hz, the peak frequency of vertical vibration of the bridge appeared at 100 Hz, and the peak frequency of transverse vibration of the bridge appeared at 63 Hz. (2) The dominant frequency range of A-weighted sound pressure level at each field point in the test was 63 to 1 250 Hz. (3) The local vibration response of the steel web in the steel-concrete composite bridge was prominent, and the acceleration effective value can reach 6 to 10 m/s², significantly higher than the vertical and transverse vibration of the bridge. (4) The noise pressure level of the railway boundary field point can reach 75 to 78 dB(A). (5) The research results can provide measured data support for railway steel-concrete composite beam bridge engineering and research.

Research purposes: To verify the feasibility of applying textile reinforced concrete (TRC) to bridge strengthening, this paper investigates the flexural performance of TRC strengthening old hollow slab beams based on four-point bending tests in the field to address the problems of inadequate load carrying capacity and large deflection of in-service reinforced concrete (RC) bridge main beams.
Research conclusions: (1) The specimens mainly suffer from the failure modes of fracture of the textile, relative slip of the textile and the matrix, local debonding and interlaminar peeling, and the load carrying capacity is increased by 9.09%~30.3% by TRC reinforcement. (2) TRC reinforcement reduces the deflection of hollow slab beams by 8.4% to 26.8%, effectively improving their stiffness and limiting the development of cracks, but reducing ductility by 13.8% to 31.9%. (3) The optimum textile lap length obtained from this test is 400 mm. (4) The load carrying capacity of TRC reinforced hollow slab beams is calculated, and the theoretical value is in good agreement with the test value. (5) The research results have certain guiding significance for the application of TRC in the strengthening of bridge projects.

Research purposes: Rockburst disasters are most prominent in the construction of deep-buried high-ground stress hard rock tunnels, and the clear influence of the main factors affecting the occurrence of rockbursts is of great significance for the prediction and prevention of rockburst disasters. This paper takes a new mountain TBM tunnel in southwest China as the engineering background, based on the summary analysis of the conditions of rock explosion, based on the FLAC3D software to establish a numerical model of the TBM tunnel boring, analyze the impact of the ground stress and the strength of the surrounding rock on the propensity to rock explosion; and then use the game combination of empowerment-gray correlation analysis to determine the degree of influence of different factors on the propensity to rock eruption.
Research conclusions:(1) High energy storage brittle rock mass, sufficient energy source, and engineering excavation unloading are the conditions for the occurrence of tunnel rockburst. (2) Rockburst propensity increases gradually with the increase in depth of burial. Lateral pressure coefficient <1.0, the side wall of the largest rock explosion tendency; lateral pressure coefficient >1.0, the arch (arch bottom) at the largest rock explosion tendency. With the increase in lateral pressure coefficient, the arch and arch shoulder rock explosion propensity gradually increased, and the side wall rock explosion propensity gradually decreased. (3) The rockburst tendency increases slightly with an increase in cohesion. When the internal friction angle is small, the rockburst tendency increases with the increase of the internal friction angle, but the larger the internal friction angle, the smaller the influence on the rockburst tendency. (4) The degree of influence of different factors on the rockburst propensity is burial depth > internal friction angle > lateral pressure coefficient > cohesion. (5) The results of this study can provide support for the determination of influencing factors of rockburst prediction in high-ground stress tunnels and also provide a reference for the prevention and control of rockburst disasters.

Research purposes: The complex geological conditions and fragile environment in mountainous areas make the construction of railway tunnels arduous in terms of environmental protection, soil and water conservation, etc. It is imperative to reduce the disturbance of tunnel construction to the regional environment and balance the relationship between tunnel construction and environmental stability. To clarify the key nodes of green coordinated development of "tunnel-environment" and formulate targeted strategies to reduce the adverse impact of tunnel construction on the regional environment, an analysis method of key green elements of "tunnel-environment" in mountain railway based on a multi-layer coupling network model is proposed.
Research conclusions: (1) Based on clarifying the interaction relationship of the "tunnel-environment" in mountain railway, build an element system that includes tunnel green, interface, and environmental elements. Using the multi-layer coupling network model, each element is abstracted as the node of the network at different levels, and the organic relationship of each node in and between the network layers is established, which can establish the basis for the quantitative expression of the interaction relationship of the "tunnel-environment". (2) Taking a railway tunnel engineering in a mountainous area as an example, the network node importance assessment method is used to identify seven key green elements: tunnel section size, tunnel excavation length, tunnel blasting mode, tunnel ventilation mode, tunnel lining waterproof design, tunnel grouting and water plugging, tunnel ventilation equipment layout, which should be optimized and controlled. (3) The research results are in line with the engineering practice, and verify the applicability of the model, which can provide a basis for determining the key points to reduce the stress effect of railway tunnel construction in mountainous areas on the regional environment.

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: 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: 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: 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: To investigate the seismic response characteristics of the bridge-track-catenary system under different longitudinal resistances, a sophisticated simulation model was established, taking the example of a 7× 32 m double-track simply supported box girder installation. The influence of longitudinal resistance on the seismic response of each component in the system was explored, the response characteristics of different components under various seismic waves were analyzed, and the impact of the catenary structure on the track-bridge system was also revealed.
Research conclusions: (1) The longitudinal resistance significantly affected the stress on steel rails and the longitudinal deformation of fasteners. Moreover, the implementation of a ballastless track system notably reduced the deformation of fasteners at the piers while increasing the stress on rails at both ends of the bridge piers. Under the action of El-Centro seismic wave, the longitudinal deformation of fasteners under longitudinal resistance of ballastless rail fasteners is 16.7% and 15.0% lower than that under ballasted track and small resistance fasteners respectively. (2) The seismic response of the catenary structure and the bridge structure showed minor sensitivity to longitudinal resistance. (3) Under different longitudinal resistances, the impact of El-Centro wave on the bridge structure and track structure was greater than that of the Taft wave. Specifically, under the El-Centro seismic wave, the bridge stress was 9.6% higher for smaller fastenings and 7.4% higher for the ballast track compared to the ballastless track. (4) The presence of the catenary structure influenced the overall stiffness of the system. Considering the catenary, the bridge stress and the bottom shear force of the bridge piers significantly increased. It is recommended that during the design of high-speed railway bridges in seismic regions, the influence of the catenary structure should be taken into account. (5) The research results can provide reference for the seismic design of the track structure on the bridge.

Research purposes: Due to the complexity, sequence, space and openness of investment consumption factors in subway construction projects, the existing fixed investment control mode has far failed to meet the requirements of investment randomness and nonlinear evolution, and it is urgent to reform the subway investment control management mode. Therefore, this paper comprehensively uses BIM, Python technology, fuzzy mathematics, BP neural network, acquired value theory and PDCA cycle method to build an intelligent prediction and control method for subway construction investment.
Research conclusions: (1) The basic database of subway construction investment is established, and the cause and countermeasure database of subway project investment is constructed. (2) Using SPSS factor analysis, rough set theory, fuzzy mathematics combined with BP neural network, the overall construction objective of the whole line is obtained. (3) Integrated PDCA cycle and acquired value theory carry out dynamic investment optimization control for key control projects, significantly improving the overall management efficiency and level of the project. (4) The computer aided intelligent control software for subway construction investment was established and applied in Chengdu subway construction example. (5) The research results can provide a feasible plan for the investment control of the entire subway line construction.

Research purposes: The fracture zone is one of the most common geological anomalies in tunnel construction, which is prone to gushing water and mud, landslides and other geological disasters. To help solve the problems of relying on experience and low accuracy of traditional geological prediction interpretation, an intelligent identification algorithm of tunnel fault fracture zone based on Convolutional Neural Network (CNN) was proposed to assist professionals in identifying fault fracture zone quickly and effectively.
Research conclusions:（1）Based on the geological background and standardized forecast picture data set, the YOLOv5 deep learning framework was adopted, the BoTNet module was introduced, and the self-attention mechanism was combined to form an intelligent identification algorithm for fault fracture zone (New_YOLOv5), which can realize the intelligent identification of its location, scale and other elements.（2）Compared with the traditional YOLOv5 algorithm, the optimized algorithm has a higher accuracy in identifying undesirable geologic bodies, with the growth rates of mAP as well as mAP_max values of 13.68% and 9.96%, respectively, where the highest mAP value can reach 84.79%.（3）To a certain extent, the research results can promote the further improvement of the interpretation level of the results of the over-advance prediction of tunnel fault fracture zones, and realize the technological progress from "experience-based, varying quality" to "intelligent identification, fast and effective", which can provide favorable technical support for the intelligent construction of tunnels, and has a good prospect of engineering application.

Research purposes: To improve the deformation capacity and construction efficiency of center columns in assembled subway stations, a mortise-and-tenon prefabricated column end connection was proposed. In this paper, ABAQUS finite element software was used to analyze the damage mode, force mechanism and seismic performance of prefabricated column end connections, and to compare the difference in dynamic response between assembled subway stations with mortise-and-tenon prefabricated column end connections and cast-in-place subway stations under seismic action.
Research conclusions: (1) The tenon-bolt column end joints have better load carrying capacity, deformation capacity, and energy dissipation capacity, and better seismic performance. (2) Compared with cast-in-place subway stations, the structural interstory displacement angle of the assembled subway station with tenon-bolt column end joints increases slightly, but the tensile damages of the center columns and the connection of the top base plate with the side walls are smaller. (3) The design of tenon-bolt joints effectively enhances the center columns and the connection of top base plate with side walls by releasing some of the column bottom constraints, which effectively improves the safety of the center column and enhances the collapse resistance of the structure. (4) The results of this paper have reference value for the application and promotion of dry prefabricated column end connections in subway stations.

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: 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: The mortar void disease of ballastless track directly affects the operating speed and running performance of high-speed railway line. Taking a six-span simply supported girder bridge-CRTS Ⅱ type ballastless track system and the CRH2C, CRH3 and CRH380A high-speed EMUs as the research object, the modal analysis of the ballastless track-bridge submodel is carried out based on ANSYS to obtain the overall mass, stiffness and damping matrix. Combined with HBMAT command and PYTHON language, the overall matrix is transformed into sparse matrix and imported into multi-body dynamics software together with node degree of freedom mapping file. Based on wheel-rail contact relationship, a dynamic model of track-bridge coupling system considering mortar void is finally established and verified. With the Chinese track spectrum as the initial irregularity, the track deformation caused by pier settlement based on the general representation model of bridge-rail developed by the author is the additional irregularity. Considering the randomness of fastener stiffness, mortar elastic modulus and pier settlement, the Box-Behnken method was used to design the test points based on Design-Expert software, coupled dynamics model calculation is carried out respectively to evaluate the running performance of CRH2C, CRH3 and CRH380A under different mortar void conditions and mechanical parameter randomness.
Research conclusions: (1) The established dynamics model of train-track-simply-supported beam bridge coupling system is in good agreement with the calculation results of the literature model. (2) Under the same mortar void condition, the influence on the safety index is CRH380A>CRH2C>CRH380A, and the influence on the comfort index is CRH2C>CRH3>CRH380A, the influence on the stability index of the three types of trains is basically the same. (3) After considering the randomness of parameters, the index values of safety, comfort and stability indexes are all fluctuate up and down, and the control limits of each index are upper and lower limits boundary values. Taking the upper limit boundary value as the control limit is safer and more reliable than not considering parameter randomness. (4) The research results can provide some reference for the design and checking calculation of high-speed railway simply supported girder bridge.

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: 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: 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: 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 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.