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.

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.

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.

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 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.

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

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.

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.

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.