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.

The subgrade structure of high-speed railways is an important foundation for the safe and smooth operation of high-speed trains, and the scientific design of the subgrade structure provides a fundamental guarantee of its durability and technical economy. As, in the development of high-speed railways in China, higher speeds are being pursued, more requirements have been put forward for the dynamic stability of subgrade structures. To address this issue, this article focuses on the control requirements for the long-term stability of subgrade deformation, and various design methods for high-speed railway subgrade structures are presented. Considering the energy dissipation and dynamic stability characteristics of subgrade filling materials, the dynamic performance of coarse-grained soil filling materials in the bottom layer and graded crushed stones in the surface layer are revealed. The methods for determining the values of dynamic parameters such as the dynamic modulus and damping ratio are provided. Based on the dynamic shakedown theory, the stress–strain hysteresis characteristics of fillers and the variation law of dissipated energy are revealed. The correlation between unit volume dissipated energy and shakedown state under cyclic loading conditions is identified. A criterion for determining the critical shakedown state of high-speed railway subgrade structures based on equivalent unit volume dissipated energy is proposed, and a method for determining the design threshold of dynamic stress and dynamic strain is also proposed. The results show that the shakedown design critical values of equivalent unit volume dissipated energy in the bottom and surface layers of the foundation were between 0.0103~0.0133 kJ/m³ and 0.0121~0.0149 kJ/m³, respectively. The critical dynamic strain range was 0.8 × 10⁻³~1.3 × 10⁻³. On this basis, a high-speed railway subgrade design method based on energy dissipation and dynamic shakedown characteristics was developed. The results can provide theoretical support for the design of high-speed railway subgrade structures with different filling material alternatives and control standards.

The unified hardening model for clays and sands (CSUH) can adequately represent the stress–strain characteristics of various soil types. However, being an incremental elastoplastic constitutive model, the CSUH model requires extensive iterative computations during parameter identification, resulting in significant computational time. To improve computational efficiency, this study derives the elastoplastic compliance matrix and stress–strain incremental relationships under different stress paths, eliminating the repeated solving of equations typically required during iterative processes. Furthermore, a dynamic step size iterative method is proposed based on the changing slope characteristics of the stress–strain curves. This method divides the total axial strain into two segments: in the initial segment (approximately the first 30% of total strain), where the curve slope is steep, smaller step sizes with arithmetic progression distribution are employed, while in the latter segment (approximately the remaining 70%), characterized by a gentle curve slope, larger and uniformly distributed step sizes are adopted. Comparative analyses between the proposed dynamic step size method and the traditional constant-step iterative method demonstrate that, under the premise of ensuring calculation accuracy, the dynamic step size method significantly reduces the iteration steps from 3000 to 50, thus decreasing the computational time by approximately 47 times. Finally, the proposed method is applied to parameter identification of Fujinomori clay, calcareous sand, and Changhe dam rockfill materials using the CSUH model. The predictions closely match experimental results, confirming the CSUH model’s capability in accurately describing the mechanical behaviors of different soils under various stress paths. The dynamic step size iterative approach developed in this study also provides valuable insights for enhancing computational efficiency and parameter identification of other elastoplastic constitutive models.