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.

This paper presents laboratory and field test results on the use of tire cell track foundation (TCTF) consisting of an assembly of infilled rubber tires to reinforce capping material below the ballast layer. Large-scale cubical triaxial tests were carried out with two different infill materials (crushed basalt rockfill and recycled spent ballast) and they were subjected to varying cyclic loading magnitudes and frequencies. A multistage cyclic loading was performed with and without the inclusion of tire cell reinforcement, whereby the cyclic loading was applied in four different stages with 25,000 loading cycles in each stage. In the first two stages, the frequency was increased from 10 to 15 Hz for an equivalent axle load of 25 t. For the third stage, the axle loading was increased to 35 t with a frequency of 10 Hz, which was then increased to 15 Hz in the final stage. The results showed that the TCTF could reduce the vertical stress transmitted to the subgrade layer as well as curtail the vertical and lateral displacement of the ballast layer. The TCTF further stabilized the track without any significant reduction of the resilient modulus of the overlying ballast as the loading and frequency increased. Compared to a traditional track, the TCTF showed a reduction of 40.1% and 28.3% in the breakage index for the crushed latite basalt and spent ballast (i.e., recycled from ballast tips) infilling the tire cells, respectively. Test results confirm that the TCTF can significantly improve the overall track performance, and this could be mainly attributed to the increased confining pressure provided by the tire cell assembly, as well as the enhanced damping properties of the rubber tire inclusions. In addition, the concept of TCTF was tested using a fully instrumented track (20 m long) subjected to the passage of a 22-t locomotive with two fully loaded carriages. The trial was constructed within a maintenance yard for heavy haul rolling stock located in a western suburb of Sydney, Australia. Field measurements revealed that, compared to the standard track, the TCTF significantly reduces stress transfer to the subgrade soil. This ultimately mitigates excessive deformation and subgrade failure, making TCTF a sustainable solution for soft and weak subgrade soils despite initial settlement.

Evaluating the mechanical properties of deep soil mixing (DSM) requires destructive borehole coring because they are mainly situated underground. Although surface wave method offers potential for quality assurance, its complexity arises from multi-mode phenomena and the need to re-evaluate inversion results, often necessitating manual interpretation. This paper presents a data-driven surface wave framework to retrieve field DSM profile Vs over time, incorporating a mode-free forward operator and the Monte Carlo Tree Search (MCTS) inversion. Validations using synthetic data affirmed the framework's accuracy and efficiency in tracking subsurface shear wave velocity. In a real-world DSM site, the proposed method successfully captures the mechanical properties evolution across two DSM layers over the curing period, aligning well with site investigations and borehole coring. This pioneering monitoring framework integrates geotechnical engineering with geophysics expertise, underscoring the value of non-destructive seismic methods for measuring subsurface property evolution.

Streambed scour in cohesive sediment is complex because erosion processes depend on the physical, geochemical, and biological properties of the sediment. The scouring processes can also be characterized as a slow fatigue phenomenon. Therefore, repetitive hydraulic loadings from multiple stormflow events are likely necessary for equilibrium scour depths to develop in cohesive sediment compared with non-cohesive sediment. Cumulative effective stream power, which is a surrogate measure of effective stream power duration, showed a significant relation with scour development and propagation in cohesive sediments around bridge piers, where results from this study identified a statistically significant correlation between cumulative effective stream power and the observed scour depths around different bridge piers (R-2 = 0.56, p < 0.001). However, some localized and site-specific variations were observed. It was also observed that scour depth development in cohesive soil appeared to be dependent on effective shear duration, rather than the number of flow events above erosion threshold values. In addition, the relationship between an erodibility index (K) and critical stream power showed a significant statistical correlation (R-2 = 0.61, p = 0.017). Results from this study deviated from the Annandale empirical relationship for sediments when K < 0.1. This finding supports that site-specific critical stream power should be measured using an empirical relationship for cohesive bed sediments to predict scour depths.

With the rapid development across major cities, low-capacity screw piles are adopted by builders as a viable economical option in managing risk involving settlement in soft soil deposits. Although the required installation torque and the capacity of a screw pile can be correlated to the soil shearing resistance at the interface of its shaft and helical plates, the correlated ultimate capacity of the pile is specific only to undrained conditions. Therefore, if the water table fluctuates within the embedment length of the pile, the correlated ultimate strength is not valid. This poses a serious design concern in over-consolidated fills. Therefore, due to the uncertainty associated with the compressive capacity of installed screw piles in soft saturated deposits, it is advantageous to perform a static load test to verify the serviceability and ultimate loads. In this study, four static load tests were carried out on screw piles at four different construction sites in the city of Melbourne, to study the load transfer mechanism at various levels of axial loading and subsequent unloading/reloading stages. In one of the sites, the screw pile was equipped with miniature transducers to monitor the generated total stress and pore-water pressure during the installation and post-installation. The results of this study indicated that a static load test can accurately estimate the real bearing capacity of a screw pile which differs significantly from the design geotechnical strength calculated using theoretical equations. It was concluded that in the absence of a pile load test, it is rational to adopt a geotechnical reduction factor of 0.4 and neglect the skin friction capacity of the screw pile to provide a safe foundation design.

When constructing superstructures on soft soils, geogrid-reinforced embankments and pile-supported embankments are used widely to improve the soft foundation and prevent issues including excessive settlements and large lateral displacements, so it is crucial to understand and evaluate their performance systematically. This study focuses on a case of piled embankments for a motor-racing circuit under construction in China. Two large-scale field tests of pile-supported embankments with and without reinforcement were carried out to investigate the effect of geosynthetic reinforcement on the improvement of embankments. During long-term monitoring, instruments in the test sites measured earth pressures, settlements, lateral displacements, and pore water pressures, and the performances of the reinforced or unreinforced embankments were examined. Test results from the two test sites under similar loading are compared, and it is concluded that the geosynthetic-reinforcement considerably influences the improvement of load transfer and diminishment of total and differential settlements. The lateral restraint provided by the geogrids also reduced the lateral soil displacement and the influence of subsoil depth. The smaller excessive pore water pressures in the site with reinforcement were associated with the enhanced load transfer due to the geogrids. This study provides an important reference for the design and construction of this circuit and other related projects.