Soil stabilization technology has been applied for a long time in the infrastructure construction field. Currently, the use of waste materials as stabilizer is growing in attention, because it promises to develop green and high-performance soil stabilization efficiency. In this work, three common waste materials, including rice husk ash (RHA), steel slag (SS) and iron tailing (IT) powder, were selected and synergistically utilized with cement to prepare stabilized soil. The mechanical strength, hydration degree and microstructure of the stabilized soil samples were tested. The experimental results showed that the mechanical strengths of the samples were improved as the cement content increased. To be specific, RHA-blended samples exhibited the lowest strengths compared with those incorporating SS and IT, indicating the poor effect of RHA on stimulating strength improvement. Moreover, SS and IT showed a much more significant effect on enhancing the mechanical strength for the stabilized soil samples, and the strength increasing rates can reach up to 60% compared to the reference batch. In addition, microstructural analysis results further verified the benefits of cement and waste materials on improving the performance of stabilized soil samples, as the hydration reaction and pore structure were proven to be improved with the aid of waste materials. This work gives insights into environmentally friendly road construction with high utilization of selected common wastes.

Part of the Hang-Tai High-speed Railway (Hangzhou via Shaoxing to Taizhou in Zhejiang Provence) in China passes through the diatomaceous earth area, which is the first time in the history of Chinese high-speed railway construction. This type of soil has significant compressibility, swelling and disintegration. Diatomaceous earth also shows a sharp reduction in strength when exposed to water, which severely impacts the safety of the project. However, no studies have been carried out on the engineering practice of building a high-speed railway in the diatomaceous earth area in China. Moreover, there is limited experience in the construction of ballastless track through the diatomaceous earth area. In order to ensure the stability of the high-speed railway subgrade in diatomaceous earth area, and considering the high level of precipitation in the location of this railway, a kind of waterproof and drainage subgrade (WDS) is proposed to reduce the influence of precipitation on the strength of the diatomaceous earth foundation. The subgrade has a flexible waterproof and drainage layer (WDL) inside, which consists of capillary waterproof and drainage plates and medium-coarse sand. In the present study, field tests including immersion tests and excitation test are carried out on a subgrade test section to verify the subgrade structure. The tests mainly focus on construction technology, waterproof performance and dynamic characteristics. The studies show that the subgrade bed with the WDL can effectively avoid the diatomaceous earth foundation from rainfall interference and maintain the long-term stability of the subgrade. The flexible WDL in WDS has a significant energy dissipation effect in comparison with the traditional subgrade (TS) filler and can play a key role in vibration damping, promoting the attenuation of dynamic response in the downward and cross-sectional directions within the subgrade. The dynamic response of the WDS attenuates along the depth. In comparison with the existing high-speed railway subgrade measured data, its dynamic response attenuation coefficient is within acceptable limits. The laying of the WDL does not change the subgrade dynamic characteristics transfer law. The proposed structure meets the requirements of ballastless track construction for high-speed railways, and the WDL can be used in the design of high-speed railways for enhanced drainage protection in diatomaceous soil areas or other special soil areas.

Accurate settlement prediction for high-speed railway (HSR) soft foundations remains challenging due to the irregular and dynamic nature of real-world monitoring data, often represented as non-equidistant and non-stationary time series (NENSTS). Existing empirical models lack clear applicability criteria under such conditions, resulting in subjective model selection. This study introduces a Monte Carlo-based evaluation framework that integrates data-driven simulation with geotechnical principles, embedding the concept of symmetry across both modeling and assessment stages. Equivalent permeability coefficients (EPCs) are used to normalize soil consolidation behavior, enabling the generation of a large, statistically robust dataset. Four empirical settlement prediction models—Hyperbolic, Exponential, Asaoka, and Hoshino—are systematically analyzed for sensitivity to temporal features and resistance to stochastic noise. A symmetry-aware comprehensive evaluation index (CEI), constructed via a robust entropy weight method (REWM), balances multiple performance metrics to ensure objective comparison. Results reveal that while settlement behavior evolves asymmetrically with respect to EPCs over time, a symmetrical structure emerges in model suitability across distinct EPC intervals: the Asaoka method performs best under low-permeability conditions (EPC ≤ 0.03 m/d), Hoshino excels in intermediate ranges (0.03 < EPC ≤ 0.7 m/d), and the Exponential model dominates in highly permeable soils (EPC > 0.7 m/d). This framework not only quantifies model robustness under complex data conditions but also formalizes the notion of symmetrical applicability, offering a structured path toward intelligent, adaptive settlement prediction in HSR subgrade engineering.

The non-uniform deterioration of existing subgrade fillers constitutes a critical constraint for the comprehensive speed increase of China's high-speed railway network. To characterize the evolution of uneven settlement and determine the lower limit of spatial variability deterioration for 350 km/h-designed subgrades to meet 400 km/h requirements, this study establishes a data-driven random field framework for CRTS III ballastless track-subgrade systems, integrating Rayleigh wave detection and Monte Carlo simulation. The framework reveals the attenuation and distribution patterns of dynamic indicators under spatial variability of surface and underlayer fillers, elucidates the uneven settlement mechanism induced by fill variability, and compares long-term performance evaluations based on dynamic shear strain and equivalent linear model criteria. Results shows that: graded aggregates exhibit horizontal/vertical autocorrelation distances of 17m/1.21m, while Group A/B fills measure 4.93m/0.56m. When filler variability changes, exceedance probabilities for dynamic stress/deformation remain below 0.01%, indicating limited evaluation capacity of conventional strength/deformation criteria. The proposed variability coefficient thresholds, derived from dynamic shear strain and equivalent linear models, provide theoretical foundations for speed-up assessments. These robustness-based findings offer theoretical support for both new high-speed railway subgrade design and condition evaluation of existing infrastructure