Evolution patterns and characteristics of ballasted track bed lateral resistances in cold regions under progressive freezing of ice layers

The freezing process of ballasted track beds in cold regions is a dynamically evolving phenomenon. Co-regulated by factors such as ice content, freezing temperature, and freezing zone, this process exacerbates the complexity of the evolution of ballast bed lateral resistance. To address this, a combination of full-scale ballast bed lateral resistance tests, uniaxial compression tests, the discrete element method (DEM), and response surface optimization design (D-optimal design) was employed to investigate the macro-mesoscopic impacts of progressive ice layer freezing on the evolutionary process of ballast bed lateral resistance. Firstly, a full-scale ballast bed was constructed to conduct lateral resistance tests. Subsequently, ballast-ice composites were prepared under various temperatures to perform uniaxial compression tests. Following this, a DEM model of the ballasted bed was established, into which a parallel-bond model was incorporated to simulate the ballast-ice composites. Both types of DEM models were validated through comparison with experimental results. A set of progressive freezing conditions was then designed using the D-optimal method. Combined with the DEM simulation results of the ballast bed resistance under different freezing conditions, a predictive model for the lateral resistance of the ballasted bed was established, coupling ice content, freezing temperature, and freezing depth. Concurrently, based on the DEM models under varying freezing conditions, the mesoscopic mechanism of how those three factors affect the evolutionary characteristics of the lateral resistance was analyzed. The results indicate that ice content and freezing depth are the dominant factors influencing the lateral resistance of the ballasted bed, both exhibiting a significant positive correlation. The influence of temperature is relatively weak but manifests indirectly through interactive effects. Mesoscopic analysis reveals that progressive ice layer freezing inhibits particle movement within the ballast bed by increasing the number of ballast-ice parallel bonds, elevating the particle coordination number, and strengthening the force chain network. Consequently, the ballast bed transforms from a friction-dominated loose system into a cohesive-frictional composite stable system. The findings of this study elucidate the evolutionary patterns and mesoscopic strengthening mechanisms of ballast bed lateral resistance under progressive ice layer freezing. Hoping those findings can provide a theoretical foundation for the design, maintenance, and service performance evaluation of ballasted tracks in cold regions.