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.

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.

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.

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 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.

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 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.

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.

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.

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.