A comprehensive series of tests, including dynamic triaxial, monotonic triaxial and unconfined compressive strength (UCS) tests, were carried out on reconstituted landfill waste material buried for over twenty years in a closed landfill site in Sydney, Australia. Waste materials collected from the landfill site were treated with varying percentages of cement, and both treated and untreated specimens were investigated to evaluate the influence of cement treatment. The study examined the dynamic properties of cement-treated landfill waste, including cumulative plastic deformation, resilient modulus, and damping ratio, and also analysed the impact of cyclic loading on post-cyclic shear strength in comparison to pre-cyclic shear strength. The UCS tests and monotonic triaxial tests demonstrated that untreated specimens subjected to monotonic loading exhibited a progressive increase in strength with rising axial strain, whereas cement-treated specimens reached a peak strength before experiencing a decline. During cyclic loading, with the inclusion of cement, a significant reduction in cumulative plastic deformation and damping ratio was observed, and this reduction was further enhanced with increasing cement content. Conversely, the resilient modulus showed substantial improvement with the addition of cement, and this enhancement was further amplified with increasing cement content. The formation of cementation bonds between particles curtails particle movement within the landfill waste material matrix and prevents interparticle sliding during cyclic loading, leading to lower plastic strains and damping ratio while increasing resilient modulus. Post-cyclic monotonic testing revealed that cyclic loading caused the partial breakage of the cementation bonds, resulting in reduced shear strength. This reduction was higher on samples treated with lower cement content. Overall, the findings of the research offer crucial insights into the possibility of cement-treated landfill waste as a railway subgrade, laying the groundwork for informed design decisions in developing transport infrastructure over closed landfill sites while using landfill waste materials available on site.

The foundation conditions of piers for multi-span long-distance heavy-haul railway bridges inevitably vary at different locations, which may lead to non-uniform ground motions at each pier position, potentially causing adverse effects on the bridge's seismic response. To investigate the seismic response of bridges and the running safety of heavy-haul trains as they cross the bridge during an earthquake, a three-dimensional heavy-haul railway train-track-bridge (HRTTB) coupled system model was developed using ANSYS/LS-DYNA. This model incorporates the nonlinear behavior of critical components such as bearings, lateral restrainers, piers, and wheel-rail contact interactions, and it has been validated against field-measured data to ensure reliable dynamics parameters for seismic analysis. A multi-span simply supported girder bridge from a heavy-haul railway (HHR) was employed as a case study, in which a spatially correlated non-stationary ground motion field was generated based on spectral representation harmonic theory. Comparative analyses of the seismic responses under spatially varying ground motions (SVGM) and uniform seismic excitation conditions were performed for the coupled system. The results indicate that the presence of heavy-haul trains prolongs the natural period of the HRTTB system, thereby appreciably altering its seismic response. At lower apparent wave velocities, more piers exhibit a low-response state, and some pier bases enter the elastic-plastic stage under local site effects. Compared with the piers, the bearings show higher sensitivity to seismic inputs; fixed bearings experience damage when subjected to traveling wave effects and local site effects, which is subsequently followed by the failure of lateral restrainers. Train running safety is markedly reduced when crossing local soft soil site conditions. The conclusions drawn from this study can be applied in the seismic design and running safety assessment of HHR bridge systems under SVGM.

This study evaluates the dynamic behavior of a subsea railway tunnel during an earthquake, considering ground conditions and seismic wave characteristics using the finite difference modeling method. A comprehensive ground-tunnel structure system model was constructed to analyze the structure's response during earthquakes, yielding significant results. Analysis of lining stress values in the subsea tunnel revealed that the maximum compressive stress in the soil part is significantly larger than in the rock part in composite ground conditions, and the maximum compressive stress in the fractured zone is increased by up to 10 times compared to the rock zone. In addition, a seismic fragility curve for subsea tunnels was derived from a series of analytical results. The analysis indicates that the probability of minor damage exceeds 50 % for earthquakes of about 0.32 g and above, while the probability of moderate damage exceeds 50 % for earthquakes of 0.39 g and above for subsea railway tunnels passing through various ground conditions.

Aeolian sand along the Hojiakueri Railway in the Taklimakan Desert exhibits poor mechanical properties for direct use as a filler for railway subgrades. Although cemented soil reinforced with single fibers can improve mechanical properties, its limited effectiveness and high cement usage pose significant economic and environmental concerns. This study investigated the improvement of splitting tensile strength (STS) in cemented aeolian sand through hybrid fiber reinforcement. An orthogonal test was designed to evaluate four factors-fiber types (pairwise combinations of basalt, polypropylene, and glass fibers), fiber lengths (3, 6, and 9 mm), hybridization ratios (1:1, 1:3, and 3:1), and fiber contents (4 %o, 8 %o, and 12 %o) - along with their interactions. The performance of cemented aeolian sand reinforced with hybrid fiber (CASRHF) was evaluated through STS tests and scanning electron microscopy (SEM). The results identified the optimal combination as a 1:1 mix of 6 mm basalt and polypropylene fibers with a fiber content of 12 %o. The interaction between hybrid fiber type and fiber length was the most critical factor influencing STS, followed by hybrid fiber type, fiber length, and fiber content. SEM analysis further revealed a linear negative correlation between STS and porosity, providing new insights into the microscopic mechanisms. The findings underscore the importance of optimizing hybrid fiber combinations to meet the performance requirements of railway subgrade beds in aeolian sand regions.

A series of large-scale shaking table tests was conducted on a pile network composite-reinforced high-speed railway subgrade. The displacement, peak acceleration amplification factor, dynamic soil pressure, and geogrid strain data were used to investigate the dynamic characteristics. The Hilbert-Huang transform spectrum, marginal spectrum, and damping ratios were used to study the seismic energy dissipation characteristics and damage evolution mechanisms of the reinforced subgrade. The results indicate that the graded loading of seismic waves induces a global settlement phenomenon within the subgrade, the displacement phenomenon of the slope is more evident, and the reinforcement effectively mitigates the amplification effect of the peak acceleration along the elevation. The peak and cumulative residual dynamic soil pressures were most significant near the bedding layer, and the upper and middle parts of the subgrade exhibited superior stabilization performance. The geogrid reduced the local vibration variability and enhanced the overall stability. The damage evolution in the middle part of the subgrade was relatively gentle, whereas the slope exhibited a multistage development trend. The internal damage of the subgrade grows slowly at 0.1-0.2 g, faster at 0.2-0.6 g, and rapidly at 0.6-1.0 g.

The rail network invariably encounters soft subgrades consisting of shallow estuarine clayey deposits. Cyclic loading generated by the passage of trains causes deformation and corresponding development of excess pore water pressure (EPWP), which dissipates during the rest periods between two consecutive trains. This paper presents an experimental study describing the effect of yield stress and EPWP responses upon intermittent cyclic loading (i.e. with rest periods), and the associated consolidation with the combination of vertical and radial drainage by way of a prefabricated vertical drain (PVD). Based on the laboratory data, the normalised yield stress for cyclic loading (NYCL) is introduced as an insightful parameter to define a novel empirical relationship between the yield stress, cyclic stress amplitude and the initial effective stress. The experimental results indicate that, as the NYCL increases, the peak EPWP decreases and, during the rest periods, the EPWP reaches a stable equilibrium faster without causing further settlement. Furthermore, this study demonstrates that the accumulated EPWP caused by cyclic loading can be further reduced when using a larger width of PVD for a given unit cell radius. An analytical model inspired by empirical parameters for predicting EPWP is proposed, capturing the effects of NYCL and the PVD characteristics.

It is necessary to fully understand the settlement of high-speed railway subgrade induced by train loading to ensure the operation safety of high-speed trains. A 1:7 reduced-scale model test was designed to investigate the settlement of subgrade under two loading methods: continuous and intermittent cyclic loading. The testing results show that an increase in load amplitude enhances the load transmission effect to the bottom of the subgrade. After 105 cycles of continuous loading, the cumulative settlement of the subgrade at depth of 0, 20, and 40 cm directly below the loading range is 3.247, 1.05, and 0.09 mm, respectively, showing significant decreases with depth. A significant rebound can be observed when the applied load is removed during the intermittent loading process, which is quite different from the results under condition of continuous loading. Thus, the intermittent effect of train load on the cumulative deformation of the subgrade cannot be ignored. In addition, to better predict the cumulative settlement of the subgrade, a prediction method based on the state evolution model was proposed and used to quantitatively analyze the testing observations. Based on the state evolution model, the predicted cumulative strains at depths of 0, 20, and 40 cm were 1.218%, 0.457%, and 0.047%, respectively, which are in good agreement with the experimental results of 1.099%, 0.48%, and 0.045%, indicating that the theoretical model can accurately predict the cumulative strain of the subgrade caused by train load. Additionally, the parameters of the state evolution model can be updated in a timely manner by applying the updated monitoring data to enhance the prediction accuracy. The current work provides an alternative method for predicting the long-term cumulative settlement of subgrade induced by the train loading, and also a basis for the optimization of high-speed railway subgrade design.

The construction of high-speed railway in Southwest China must traverse extensive regions of red mudstone. However, due to the humid subtropical monsoon climate in Southwest region, the red mudstone is often exposed to a high-water content or saturated state for extended time, and the poor mechanical properties under such condition cannot satisfy the requirements of high-speed railway subgrade. This paper proposes the use of lime and cement to improve the saturated unconfined compression strength (UCS) of the red mudstone fill material. Comprehensive tests, including UCS tests and scanning electron microscopy, were conducted on cement-lime modified red mudstone. Results show that lime stabilisation can significantly enhance the UCS and elastic modulus with the increase of dry density and modifier content. For the specimens with 4% lime and 6% cement, both peak strength and elastic modulus of the modified samples are more than 10 times higher than those of the untreated ones. The modulus exhibits nonlinear degradation with the development of shear stress, but the degradation can be improved with the increase of dry density and modifier content. At 60% of initial tangent modulus, the corresponding stress for untreated soil, lime stabilised and cement-lime modified filler are 0.74, 0.92 and 0.99. As for the energy evolution, the increasing dry density can enhance elastic and dissipated energies through denser particle arrangements, while a higher modifier content raises total energy. When the cement content is 6%, the total energy is more than 8 times higher than that of the untreated material, reflecting increased brittleness to a sudden fracture. The improvements are attributed to the formation of acicular and platy hydration products, which can tighten the pore structure. The study underscores the importance of lime and cement in ensuring subgrade stability for high-speed railways in Southwest China's red bed regions.

This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials (CREFMs) using a novel unsaturated large-scale triaxial apparatus equipped with the axis translation technique (ATT). Comprehensive soil-water retention and constant-suction triaxial compression tests were conducted to evaluate the effects of initial void ratio, matric suction, and confining pressure on the properties of CREFMs. Key findings reveal a primary suction range of 0-100 kPa characterized by hysteresis, which intensifies with decreasing density. Notably, the air entry value and residual suction are influenced by void ratio, with higher void ratios leading to decreased air entry values and residual suctions, underscoring the critical role of void ratio in hydraulic behavior. Additionally, the critical state line (CSL) in the bi-logarithmic space of void ratio and mean effective stress shifts towards higher void ratios with increasing matric suction, significantly affecting dilatancy and critical states. Furthermore, the study demonstrated that the mobilized friction angle and modulus properties depend on confining pressure and matric suction. A novel modified dilatancy equation was proposed, which enhances the predictability of CREFMs' responses under variable loading, particularly at high stress ratios defined by the deviatoric stress over the mean effective stress. This research advances the understanding of CREFMs' performance, especially under fluctuating environmental conditions that alter suction levels. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Research on the dynamic response of subgrades is essential for designing heavy-haul railway subgrades. Therefore, a dynamic stress field test was carried out on the Daqin Railway using a three-dimensional dynamic soil pressure box capable of measuring the total stress component of soil elements. Then, a train-track-subgrade coupling finite-element model (FEM) considering the track irregularity and infinite element boundary conditions was established, and the validity of the model was verified using field test results. Subsequently, based on the field test results, the actual three-dimensional dynamic response and stress path of the subgrade under a train load were analyzed. Based on the FEM results, the effects of the train axle load, train speed, subgrade stiffness, and subgrade thickness on the three-dimensional dynamic response of the subgrade were analyzed, and a prediction model of the vertical dynamic stress was proposed. Finally, the influence of the depth of the heavy-haul train loads on the subgrade was studied. Research has shown that the normal stress caused by two wheelsets under the same bogie has a superposition effect, and each peak value of the normal stress corresponds to the center position of the bogie. When the train passes through the test section, the stress path of the soil element directly below the track is fairly elliptical, and the principal stress axis of the soil element rotates by 180 degrees. The normal stresses sigma x, sigma y, and sigma z increase proportionally with the speed and axle load of the train but decrease inversely proportional to the thickness of the ballast layer. The subgrade stiffness significantly influences the normal stress sigma x and sigma y but has no apparent influence on the normal stress sigma z. The influence depth of the train load in the subgrade is related to the axle load, train speed, and thickness of the ballast layer, but is unrelated to the stiffness of the subgrade surface layer. This study provides practical and theoretical data for analyzing the dynamic performance of heavy-haul railway subgrades.