With the development of high-speed railways towards 400 km · h^-1 and higher speed levels, train operation safety and ride comfort impose more stringent requirements on track regularity. Focusing on track regularity of simply-supported bridges with common spans widely used in high-speed railways, a refined track-bridge finite element model is established to reveal the inherent mechanism of periodic track irregularities induced by creep camber of bridge girders. Furthermore, an analysis element for periodic track irregularities on bridges suitable for dynamic simulation is proposed. Based on the established vehicle-track-bridge coupled dynamic model for higher-speed railways, the influence of periodic track irregularities on the carbody response of trains running at 400 km · h^-1 is investigated in depth. The results show that an increase in girder creep deformation directly leads to increased rail deformation, with a significant linear correlation between their amplitudes, and the peak rail deformation is always slightly lower than that of girder creep. The proposed calculation element for periodic track irregularities exhibits better consistency with the waveform variation of measured track irregularities. Under the excitation of periodic irregularities, obvious spectral peaks appear at the harmonic frequencies corresponding to a 32 m wavelength in the carbody response spectrum, with the maximum peak occurring at the second harmonic, indicating that the carbody is more sensitive to the excitation of 16 m wavelength, resulting in a double-peak characteristic of the carbody dynamic response within the 32 m wavelength range. The findings provide theoretical support for track condition assessment and track regularity control of 400 km · h^-1 high-speed railways.

Life-cycle cost (LCC) analysis of railway bridges can provide more reasonable data support for the selection of bridge design schemes. Taking a high-speed railway bridge as an example and in combination with the bridge span requirements, two design schemes were proposed: cable-stiffened continuous rigid-frame superstructure and an arch-stiffened continuous rigid-frame superstructure. Based on the budgetary estimate, the construction costs for both design schemes were calculated. Accounting for the uncertainties inherent in the time-variant performance degradation of cables, a time-variant model for the calculation of the failure probability of the cable and hanger system during bridge operation was established to determine the optimal timing for cable and hanger replacement. For maintenance activities such as cable replacement and arch rib painting, the operation and maintenance costs of the two design schemes were calculated and the influence of the time value of capital on the operation and maintenance costs was analyzed. Addressing the uncertainties present in both the cost data and the calculation model, the distribution ranges of the LCCs for the two design schemes were presented. The results indicate that the costs of inspection, maintenance, and reinforcement during bridge operation significantly impact life-cycle costs. The life-cycle cost analysis method proposed in this study can effectively predict the maintenance timing during the operation period, providing support for accurate estimation of life-cycle costs. In the process of life-cycle cost analysis, it is necessary to fully consider the uncertainties during construction and operation, as well as the time value of costs. For the bridge in the case, from the perspective of life-cycle costs, the cable-stiffened continuous rigid-frame bridge design scheme has greater advantages, offering a reference for the selection of design schemes for similar long-span railway bridges.

To further enhance the intelligent recognition, assessment, early warning, and active prevention and control capabilities of high-speed railways in responding to risks such as natural disasters, perimeter invasion/foreign object intrusion, and external environmental safety, a method for active perception and early warning of the operational environment safety of high-speed railways is proposed based on the concept of active control of high-speed railway operating environment safety. By analyzing the action mechanism and spatiotemporal evolution patterns of the main influencing factors on the operational environment safety of high-speed railways, the disturbance mechanisms of various risk sources on train operation are revealed. On this basis, a situational awareness method for the operating environment safety across full spatiotemporal scenarios is designed, covering refined forecasting of meteorological disasters, multi-modal fusion-based recognition of perimeter invasion/foreign object intrusion, and intelligent perception of external environmental hazards through air-space-ground collaboration. Corresponding intelligent assessment and early warning models are then constructed, and active control and emergency response strategies are formulated. The results show that the accuracy of refined gale situational awareness for wind speed forecasting reaches 93%. Compared with the existing similar intelligent methods, the transmission delay of alarm information from system generation to train's beyond-visual-range terminal display is reduced from 2.364 s to 1.651 s. This method can provide a systematic solution for engineering applications and demonstrate promising prospects for practical implementation.

With the continuous advancement of infrastructure construction in western China, research on the bearing mechanisms and design methods of bridge foundations in complex terrain has become increasingly important. Focusing on the mechanical properties and structural design of embedded foundations for railway bridges in mountainous areas, this study investigates the potential failure modes of slope rock mass under combined loads. A theoretical calculation model for the embedded foundation-rock mass system under slope terrain conditions was established, revealing the interaction mechanism between the foundation and the slope rock mass. Based on this, combined with limit equilibrium theory, formulas for the ultimate bearing capacity of vertical embedded foundations and inclined arch-abutment embedded foundations under slope conditions were derived. The design rationality of the embedded foundation for the Zhongjian River Bridge was verified. The results show that the primary failure mode of vertical embedded foundations is overall shear failure of the rock mass at the pile end. As the shear force and bending moment loads outside the slope increase, the foundation-rock mass system is prone to horizontal shear failure. For inclined arch-abutment embedded foundations, the main failure mode involves combined failure at the pile end and along the pile side. The upper part of the pile foundation exhibits significant load-induced deformation, showing flexible characteristics, while the lower part mainly undergoes rigid deformation. Verification results indicate that the design parameters of both types of foundations meet bearing capacity requirements. The results provide a theoretical basis and engineering reference for the design and stability analysis of bridge foundations in mountainous areas.

With the rapid development of the railway industry and the continuous increase of passenger transport tasks, railway passenger stations are facing increasingly severe passenger flow safety issues. To realize real-time monitoring of passenger flow dynamics and finely analyze the multi-granularity characteristics of passenger flow, a Multi-granularity Yardstick for Dynamic Crowds (MYDC) model for railway passenger stations based on video analysis technology is proposed. Firstly, a passenger flow dataset for railway passenger stations is constructed. Secondly, a fine-grained feature perception network for passenger flow is designed based on YOLO and Discriminative Correlation Filter (DCF) tracking algorithm, and the adaptive crowd localization Transformer (CLTR) model for railway passenger stations is improved to capture the coarse-grained features of the overall passenger flow distribution. Finally, based on the physical attributes of passenger flow as well as its micro and macro characteristics, a Multi-Attention Spatio-Temporal Graph Convolutional Network (MASTGCN) is constructed to mine the spatio-temporal dynamic trends of passenger flow and assess the safety risk level of passenger flow in the station. The results show that the cumulative error of fine-grained feature extraction is 6.9%, the recognition accuracy of coarse-grained features is 89.1%, and the recall rate of the passenger flow safety assessment model is 87.5%. The proposed model can provide accurate data support for passenger flow management and has strong engineering application value.

By means of three-dimensional CFD numerical simulation method, the spatiotemporal distribution law of aerodynamic pressure on the tunnel wall and vehicle surface in the horizontal and vertical directions during single vehicle passage and double vehicle intersection of CR400 EMU with a speed of 400 km ∙ h^-1 is studied, and the negative pressure area and boundary conditions on the tunnel wall and vehicle surface are quantified. The results indicate that the aerodynamic pressure inside the tunnel can be correlated with parameters such as vehicle type, train speed and tunnel length to form a theoretical model. When different types of single vehicle pass through the tunnel at a speed of 400 km ∙ h^-1, the difference in peak aerodynamic pressure acting on the tunnel wall is limited. Compared with the CR400BF EMU, the CR400AF EMU only increases the positive peak of aerodynamic pressure by 1.1% and the negative peak of aerodynamic pressure by 0.9%. The aerodynamic pressure on the surface of the EMU shows high uniformity in both the horizontal and vertical directions. During single vehicle passage and double vehicle intersection, the surface of the vehicle body is basically in the same pressure state at the same time. At different tunnel lengths, when the speed of the EMU is 400 km ∙ h^-1, the negative pressure of the expansion wave at the center of the tunnel and the negative pressure of the high-speed train body itself are superimposed when a single vehicle passes through the tunnel, and the negative peak value of the aerodynamic pressure borne by the body reaches -4.60 kPa. When 2 vehicles intersect at different positions with a constant speed inside the tunnel, the maximum negative pressure occurs at the intersection condition of the tunnel center, and the negative peak value of the aerodynamic pressure reaches -9.68 kPa. When 2 vehicles intersect at a constant speed in the center of the tunnel, there is an unfavorable velocity boundary that significantly strengthens the negative pressure effect in the intersection negative pressure area.

To address the engineering problem of aggravated micro-pressure wave hazards at the portal of a 400 km · h^-1 high-speed railway tunnel, this study investigates the radiation characteristics of micro-pressure waves under the coupled effects of actual terrain and buffer structures. Based on the three-dimensional unsteady compressible Navier-Stokes equations and the SST k-ω turbulence model, and using the tunnel equivalent diameter D (10 m) as the characteristic scale, the study systematically examines the radiation characteristics, including peak wave pressure, waveform, attenuation laws, and spatial directivity, of micro-pressure waves under conditions with and without buffer structures at the tunnel exit; it also studies simple flat terrain and semi-cut-semi-fill actual terrain. The results show that the buffer structure pre-radiates micro-pressure waves through side openings, effectively reducing the intensity of micro-pressure waves in the axial direction (directly in front of the tunnel alignment, azimuth θ=0°) at the tunnel portal. The buffer structure effectively reduces the peak value and alters the waveform at 2D, but causes an increase in peak value at 8D, and also enhances micro-pressure waves in lateral directions (e.g., θ=+45°, +90°). Terrain variation has a relatively weak influence on micro-pressure waves in the tunnel axis direction but significantly affects the areas on both sides: the peak micro-pressure wave at the cut (θ>0°) is greater than that on simple flat terrain, while the peak at the fill (θ<0°) is the lowest. The cut slope has a concentrating effect on micro-pressure waves in the area below the cut top, whereas the fill terrain disperses the propagation paths, leading to lower peak values. The attenuation rate of micro-pressure waves is smallest along the tunnel axis and accelerates significantly as the azimuth angle θ increases; for the same azimuth angle, the attenuation at the cut is greater than that at the fill. The directivity of micro-pressure waves is significantly influenced by the buffer structure and actual terrain. When the propagation distance reaches 5D, the influence of the buffer structure becomes negligible, and terrain dominates the directivity - simple flat terrain exhibits axial directivity, while the semi-cut-semi-fill terrain shows directivity in the [0°, +45°] interval due to the concentrating effect of the cut and the dispersing effect of the fill. The research results provide an important theoretical basis for optimizing and design of buffer structures and terrain treatment at the portals of 400 km/h high-speed railway tunnels.

To explore the influence of grout rheological properties on the backfill grouting process, a rotational viscometer was first employed to measure the rheological behavior of cement-based grouts with different ratios, analyzing the effects of various ratios on rheological parameters. Subsequently, combined with Herschel-Bulkley model and fluid simulation software, a numerical model for backfill grouting was established. Finally, the grouting process and effectiveness under the influence of factors such as location and number of grouting holes, grouting pressure, and grout ratios were investigated. The results indicate that yield stress and consistency coefficient are primarily affected by the water-binder ratio, but this influence diminishes when the water-binder ratio exceeds 0.85. The rheological index is noticeably influenced by the water-binder ratio, bentonite-water ratio, and cement-fly ash ratio, yet exhibits poor regularity. During grout filling, the top region undergoes 4 stages of evolution, whereas other regions experience only 2 stages. Positioning grouting holes near the vault can improve the filling effectiveness in the top region, and increasing the number of grouting holes accelerates the filling rate but reduces the total grout volume during the rapid growth stage. Increasing the water-binder ratio or decreasing the bentonite-water ratio reduces yield stress, thereby enhancing filling speed and volume. Increasing grout density delays early-stage filling but benefits the accumulation of total grout volume in later stages. Since excessive pressure at middle grouting holes suppresses later-stage filling speed and volume, achieving optimal filling performance requires the maximum pressure at upper grouting holes and minimum pressure at middle grouting holes.

The 25 Hz phase-sensitive track circuit faces a broken rail detection problem due to the presence of a bypass path. As a result, the variation law of the receiving end voltage under broken rail conditions has not been clarified in the field operation for a long time. To provide a theoretical basis for eliminating potential safety hazards, based on the multi-conductor transmission line (MTL) modeling method, multiple sections along the bypass path of a 25 Hz phase-sensitive track circuit are equivalently represented as a single bypass section. A six-port network is adopted to analyze the voltage and current relationships between the broken rail section and the bypass section. These sections are linked through the impedance bond (IB) and the earth to form a coupling circuit, which is then used to establish a bypass-path model of the 25 Hz phase-sensitive track circuit and derive the corresponding MTL equations. Based on the principle of transformer mutual-inductance circuits, the voltage and current relationships of IBs at the sending and receiving ends of the broken rail section are analyzed. The boundary-condition parameter matrix of IB is derived, and the longitudinal distribution of voltage and current under broken rail conditions of the 25 Hz phase-sensitive track circuit is obtained. A decoupling algorithm based on the IB boundary-condition is proposed. The bypass-path model and the decoupling algorithm are validated through laboratory and field tests. Considering that the receiving voltage in the bypass path is non-zero under broken rail conditions, the effects of the IB connection scheme, break location, ballast leakage, and cross-bond distance on the receiving voltage are investigated. The results show that, for sections with IBs fully connected, the receiving voltage increases as the break location approaches the mid-section and as the ballast resistance increases. For sections with the sending-end or receiving-end IB disconnected, the receiving voltage increases as the break location approaches the end where the IB remains connected, and it first rises and then falls as the ballast resistance increases. When the cross-bond distance exceeds 2 km, the receiving voltage becomes nearly invariant, and 2 km can be used as a reference value. A higher receiving voltage under broken rail conditions makes broken rail detection more difficult. Therefore, it is recommended that, for sections with fully connected IBs, broken rail detection be tested using a criterion of a 40% drop in receiving voltage, whereas for sections with the sending-end or receiving-end IB connection disconnected, broken rail detection be tested by removing the single-rail connecting wire at the IB-connected end.

To optimize the layout of railway rescue trains and enhance railway emergency rescue efficiency in China,the genetic-simulated annealing hybrid algorithm is improved based on the arc risk quantification. First, a multi-dimensional risk quantification evaluation index system for the railway network is constructed. Through the Entropy Weight-TOPSIS method, risk quantification evaluation is conducted on each arc segment of the network. Then, combined with coverage theory, an optimal layout model for railway rescue trains is established with objectives including network rescue coverage rate, rescue time satisfaction, and rescue train layout cost. Secondly, the Multi-Phase Adaptive Simulated Annealing Genetic Algorithm (MP-ASAGA) is designed to solve the model. The solution process is divided into the exploration phase focusing on searching for the global optimum and the development phase focusing on accelerating convergence, with different evolutionary strategies applied in each phase to improve the algorithm's solving performance. Finally, a case study using actual railway network data from a railway bureau in China is conducted for calculation and validation. The results show that compared with the original layout scheme of the railway bureau in the case study, the optimal railway rescue train layout scheme obtained by the proposed method achieves an improvement of 8.99% in network rescue coverage rate, and an improvement of 11.62% in rescue time satisfaction. This method can provide corresponding theoretical support for the layout optimization of railway rescue trains and the enhancement of rescue efficiency.