Sand intrusion into ballasted beds seriously threatens their long-term stability and operational safety. Based on wind tunnel experiments and particle image velocimetry (PIV), this study investigated the movement of sand particles around ballasted beds in a wind-sand environment by systematically measuring and analyzing the spatiotemporal evolution of particle velocity fields, directional distributions, and flux transport. The results show that, when the wind-sand flow passes through the ballast-rail system, the flow field structure changes significantly, exhibiting clear velocity stratification and flow direction reorganization. The particle motion direction undergoes a typical evolution process of convergence, deflection, chaos, and recovery along the flow path. The directional concentration decreases from 0.959 on the windward side to 0.200 in the inter-rail region, and then rises to 0.639 on the leeward side. The particle flux attenuates by about 48% along the path, while near-surface deposition is significant, with the proportion of downward-moving particles generally exceeding 60% at all measurement positions. The ballasted bed affects wind-sand transport through the combined mechanisms of energy dissipation and screening: energy dissipation continuously weakens the sand-carrying capacity of the airflow, while the screening effect promotes sand deposition within the ballast layer.

Given the limited research on the effect of Tire-Derived Aggregate (TDA) on Steel Slag Ballast (SSB) degradation, this study employed the Los Angeles Abrasion (LAA) test to examine the mechanism of varying TDA content on SSB degradation. First, the LAA ratio, fouling index, and breakage ratio were used to analyze the effect of TDA content on degradation of SSB. Furthermore, the two-dimensional graphic information of SSB with different TDA contents before and after LAA tests was processed, and then the variation of geometric characteristics, such as surface texture and angularity of SSB, were determined to study the degradation mechanism of SSB with different TDA contents at the micro-scale. The results show that when the TDA content increases from 0% to 10%, both the LAA ratio and fouling index of SSB decrease rapidly (by 33.1% and 37.4%, respectively); when it increases from 10% to 20%, the LAA ratio and fouling index show only slight reductions (by 8.5% and 8.6%, respectively). In contrast, the breakage ratio consistently exhibits a linear decreasing trend, with an average reduction of 17.7%, indicating that increasing TDA content improved the anti-deterioration of SSB. At the micro-scale, the incorporation of TDA enhances the retention of microscopic angularity and roughness of steel slag particles by dissipating impact energy and reducing stress concentration, which is macroscopically manifested as a decreases inLAA loss, fouling index, and breakage ratio, indicating an improvement in anti-degradation performance.

To address the problem where the gauge corner of rails is prone to negative deviation due to excessive grinding, leading to reduced wheel-rail equivalent conicity and impaired running stability of Electric Multiple Units (EMUs), a rail profile optimization method considering grinding deviation is proposed. First, taking a high-speed railway as an example, statistical analysis is conducted on the deviation of measured post-grinding rail profiles to reveal the distribution characteristics of grinding deviation, and the adverse effects of negative deviation on wheel-rail contact performance are verified through vehicle dynamics simulation. Second, the measured grinding profiles are divided into training and validation sets. With the deviation between the degraded profile and the 60N profile controlled within -0.2 mm to +0.2 mm and the nominal equivalent conicity no less than 0.034 as constraint conditions, and with the the optimization objective that the contact stress for the optimized profile matched with the LMA wheel not exceed that of the LMA-60N combination, a genetic algorithm is employed to optimize seven characteristic parameters of the 60N profile, yielding the optimized profile and the degraded profile considering negative deviation caused by excessive grinding. Finally, the performance of the optimized and degraded profiles is verified through wheel-rail contact analysis and vehicle dynamics calculation; and a comparative evaluation is conducted against the standard 60N profile and two sets of field-measured grinding profiles. The results show that: in the gauge corner region (16° - 45°), the profile deviation is predominantly negative, mainly distributed in the range of -0.8 mm to 0 mm with a mean value of approximately -0.4 mm, indicating a prominent excessive grinding problem; compared with the standard 60N profile, the optimized profile matched with the LMA wheel achieves an increased nominal equivalent conicity of 0.036 and a 14% reduction in wheel-rail contact stress, exhibits comparable dynamic performance and shows improved car body lateral stability; the deviation between the degraded profile and the 60N profile is controlled within -0.2 mm to +0.2 mm, with a nominal equivalent conicity of 0.034, satisfying the design constraints and effectively resolving the problem of excessively low equivalent conicity; compared with the two sets of field-measured grinding profiles, the degraded profile demonstrates significant advantages in both dynamic and contact mechanical performance, with reductions of 19% in wheelset lateral acceleration, 7% in bogie frame lateral acceleration, and 13% in car body lateral acceleration, as well as reductions of 19% - 37% in maximum normal contact stress and 33% - 41% in maximum tangential contact stress, along with significantly reduced average contact stress and more concentrated distribution. The proposed profile optimization method provides a reference for field grinding operations and offers guidance for addressing the low conicity hunting problem of EMUs.

Uplift deformation of railway tunnel invert structures can occur under high groundwater pressure and surrounding rock swelling, inducing track irregularities and affecting the safe and smooth operation of high-speed trains. To investigate the uplift deformation patterns of ballastless track in railway tunnels, a ballastless track-tunnel invert similarity model was established based on similarity principles. The physical model was fabricated using 3D printing, and a customized loading apparatus was used to simulate and control the invert load. Results show that, under the invert load, the surfaces of all structural layers are in tension, with the central drainage channel surface exhibiting the most pronounced tension. The transverse stress is significantly greater than the longitudinal stress, making the structure more prone to longitudinal cracking, which is consistent with the field crack distribution patterns. Regarding deformation, a pronounced extrusion effect occurs at construction joints, and the central drainage channel, and as a weak part, causes the deformation at tunnel centerline to be consistently larger than that at the track bed slab centerline. With increasing invert load, the deformation amplitude increases approximately linearly, and the difference between the two widens. Moreover, insufficient invert thickness and reduced curvature significantly aggravate the occurrence and propagation of uplift deformation; a decrease in invert thickness leads to a power-law increase in uplift amplitude. The findings provide a reference for controlling tunnel invert uplift defects and optimizing structural design.

To clarify the seismic failure mechanism and develop a seismic performance evaluation method for prefabricated metro station structures in liquefiable sites, this study takes Shuangfeng Station of Changchun Metro Line 2 as an engineering case and establishes a three-dimensional soil-structure interaction numerical model using the finite difference software FLAC3D. The evolution characteristics of soil pore water pressure as well as the response laws of displacement and stress of the prefabricated station structure under different ground motions are investigated. Combined with the quasi-static test results of the prefabricated station structure, the seismic damage evolution process and failure mechanism are analyzed, and a dual-parameter seismic performance evaluation method simultaneously considering the global inter-story drift ratio and the opening amount of mortise-and-tenon joints is proposed. Subsequently, seismic fragility analyses are conducted based on both scalar and vector-valued ground motion intensity parameters. The results indicate that when the peak ground acceleration (PGA) is ≥0.2g (g as gravitational acceleration), significant liquefaction occurs in part of the site, and the onset time of liquefaction is markedly advanced with increasing ground motion intensity; the degree of liquefaction near the structure is generally lower than that in the area far from the structure. Liquefaction-induced stiffness degradation and non-uniform ground deformation significantly alter the structural load-transfer path; structural damage is mainly concentrated in the central column and the mortise-and-tenon joints of the sidewalls, exhibiting a progressive evolution from the ends of the central column toward the sidewalls and the connection zones of the arch roof and bottom slab. Even under a low axial load ratio, the central column remains the most vulnerable component. The proposed dual-parameter evaluation criterion enables a more rational assessment of seismic performance. Compared with conventional scalar intensity measures, vector-valued intensity measures more comprehensively reflect the influence of ground motion amplitude and spectral characteristics on structural failure probability, thus obtaining more reasonable fragility assessment results. The findings can provide references for the seismic design and performance assessment of prefabricated metro station structures in liquefiable sites.

To meet the requirements of modern railway bridge emergency repair, a technical scheme for a deployable medium-span emergency repair girder based on telescopic diagonal web members is proposed. The girder utilizes deployable frame units as its basic components, enabling folding and deployment through the extension and retraction of the diagonal web members. This design resolves the technical challenge of balancing assembly efficiency with storage and transportation space in existing repair girders, while also meeting the emergency repair demands of both conventional-speed and high-speed railway bridges. Finite element analysis models and multi-body dynamics models are established to conduct static analysis and vehicle-bridge coupled dynamic response analysis on the deployable railway emergency repair girder. The results indicate that the stress levels and displacements of the deployable repair girder meet the limit requirements of the “Code for Design on Railway Bridge and Culvert”. The member stresses are highest under the loading of mixed passenger and freight railway traffic. The arrangement of the diagonal web members significantly influences the ultimate bearing capacity of the deployable girder, with the inverted V-shaped configuration yielding a higher ultimate bearing capacity. Among the three truss configurations for the 32 m span, the heavy truss emergency repair girder exhibits superior dynamic response indices. The wheel load reduction rate is identified as the key factor controlling train speed, and the speed limit for high-speed trains crossing the 32 m span deployable railway emergency repair girder can be controlled at 120 km · h^-¹.

Given the significant randomness of vehicle-bridge dynamic response for higher-speed railways, this study aims to explore the characteristics and probability distribution of dynamic response of a 400 km · h^-1 train passing through a bridge. A vehicle-bridge coupled random vibration model is established based on the pseudo-excitation method and the whole-process iteration method, and its validity is confirmed through comparison with the simulation results of Monte Carlo method. Based on this model, the time-frequency distribution laws of safety and stability indices of the train running at 400 km · h^-1 are analyzed, and the random characteristics of vehicle-bridge dynamic response under higher speeds on simply-supported beams with different fundamental frequencies are studied. The results show that the statistical values of vehicle-bridge response vary with time, showing typical non-stationary characteristics. The dynamic coefficient of the bridge is mainly controlled by the arrangement of train axle and the wheelbase, and is only slightly affected by the random excitation of track irregularity. Under resonance conditions of simply supported beam, the wheel load reduction rate increases significantly with the increase of speed, and the carbody vibration acceleration is insensitive to the resonance response of the simply supported beam. The fundamental frequency of the simply-supported beam has minor effect on the wheel load reduction rate and carbody vibration acceleration, whereas the randomness of the track irregularities has a significant effect on the vertical vibration acceleration and the wheel load reduction rate of the bridge.

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.

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.

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 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.

To clarify the stress characteristics and failure mechanism of inclined bolt joints in subway shield tunnel segments, firstly, full-scale tests were designed and carried out on 2 adjacent segment standard blocks based on the supporting engineering. The stress-strain development law of concrete in each part of the inclined bolt segment joint during bearing was analyzed, and the failure process of the segment joint was studied in stages. Then, a numerical model was established to compare the failure process and characteristic change laws of segment joints under 2

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.

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 mechanism analysis and treatment of inverted arch uplift and track slab cracking in an in-service tunnel, a combined approach of field structural disease characteristic analysis and laboratory tests was adopted to explore the disease mechanism of inverted arch uplift deformation and track slab cracking in an in-service tunnel of the Shanghai-Kunming Railway. According to the analysis of structural cracking characteristics and disease mechanism, integrated treatment measures of "grouting anchor pipe installation - bedrock grouting and removal - reconstruction of inverted arch structure" was proposed. These measures were adopted to guide the construction of the background project, and the evolution laws of the contact stress between the bedrock and the inverted arch was monitored and analyzed during the construction process. The results indicated that: the expansion deformation of bedrock upon water exposure was the main cause of local uplift of the inverted arch and other supporting structures, leading to increased internal forces, uneven deformation, and cracking; factors such as bedrock bearing capacity reduction, stress concentration induced by local high in-situ stress, and uneven stiffness and stress distribution in the invert arch structure further exacerbated the risk of non-coordinated deformation and cracking in the bedrock-invert arch system; the contact stress between the bedrock and the reconstructed inverted arch showed a phased evolution pattern, initially increasing slowly and then gradually converging to stability. The average contact stresses at three monitoring sections were 167.83, 169.51 and 165.82 kPa, respectively, which ensured the stability and safety of the tunnel structure. The treatment measures in combination with the disease mechanism analysis effectively prevented and controlled inverted arch uplift and structural cracking in the in-service tunnel. The research results provide a design scheme and engineering application reference for the treatment and prevention of similar engineering diseases.

To investigate the characteristics of the initial compression wave associated with tunnel sonic boom in long high-speed railway tunnels and analyze its correlation with the occurrence of tunnel sonic boom, full-scale tests were carried out in a long tunnel. Taking the formation mechanism of tunnel sonic boom and the propagation path of the initial compression wave as the starting point, the longitudinal distributions of the aerodynamic pressure and pressure-gradient peak of the initial compression wave inside the tunnel before and after the occurrence of sonic boom were comparatively analyzed. The influence of train speed on these peak values during sonic boom occurrence was clarified, and the effects of portal hood configuration and train type on tunnel sonic boom were discussed. The results show that, under the action of nonlinear effects, the initial compression wave is progressively steepened during propagation, thereby inducing tunnel sonic boom. For the tested tunnel, regardless of whether sonic boom occurs, the aerodynamic pressure peak of the initial compression wave along the tunnel longitudinal direction first increases and then decreases. When sonic boom occurs, the pressure peak of the initial compression wave near the train exit end is higher than that near the entry end. Taking a train speed of 340 km · h^-1 as an example, the positive peak, negative peak, and peak-to-peak value of the aerodynamic pressure of the initial compression wave at the measurement point near the exit end increase by 36.53%, 11.22%, and 20.71%, respectively, compared with those near the entry end. With increasing speed, the probability of tunnel sonic boom increases, and the variation rate of the aerodynamic pressure peak of the initial compression wave from the train entry end to the middle section of the tunnel is higher than that at lower speeds. When sonic boom occurs, the pressure-gradient peak of the initial compression wave increases sharply after propagating a certain distance, and the increase near the train exit end is significantly greater than that near the entry end; at 340 km · h^-1, the difference between the two reaches nearly ninefold in the tested tunnel. When sonic boom occurs, the pressure-gradient peak inside the tested tunnel is proportional to the train speed raised to the power of 6.5-9.6, whereas when sonic boom does not occur, it is proportional to the train speed raised to the power of 3.5-4.6. In addition, compared with the recessed portal hood, the oblique portal hood is more effective in mitigating the occurrence of tunnel sonic boom.

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 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.

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.

To address the data security risks arising from the explosive growth of railway passenger transport data, the core lies in achieving intelligent identification and dynamic protection of sensitive information. Then, an intelligent identification technology for sensitive data in railway passenger tickets based on data knowledge base is proposed. Firstly, a three-level knowledge base of "laws and regulations-industry standards-enterprise norms" is constructed. Secondly, combined with historical railway passenger ticket data, a multi-level intelligent identification algorithm for sensitive data is designed, thereby efficiently and accurately identifying sensitive information in multi-modal data. On this basis, the graph technology is finally introduced to construct a data asset and sensitive data lineage graph, and based on the topological relationship of data flow, the efficient propagation of sensitive information labels among related data nodes is achieved. The results show that the sensitive information identification efficiency of the proposed technology reaches about 217 000 messages per second in structured data processing, which is almost twice as high as the traditional solution. In unstructured data processing, through domain knowledge graphs injection, the F₁ value of sensitive entity recognition is increased to 91.24%, and the context misjudgment rate is reduced to 5.88%. The accuracy of text extraction and sensitive information recognition of multimedia images reaches 93.71%. This technology can significantly improve the accuracy and processing efficiency of sensitive data identification in railway passenger tickets.

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.