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.

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.

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.

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.

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.

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.

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 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.

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.