Evaluation of fresh and recycled ballast through numerical simulation and large-scale triaxial analyses

ABSTRACT The challenge of railway ballast degradation, the limited supply of fresh ballast resources, and the limited understanding of recycling deteriorated ballast present significant issues. In this study, fresh ballast, fresh–used ballast mixtures, and laboratory-prepared used ballast were investigated to evaluate the feasibility of reusing used ballast. Discrete Element Method (DEM) simulations were employed to investigate the impact of fresh–used ballast ratios on the mechanical behavior of sheared granular packings using the Contact Dynamics (CD) method. The results showed that fresh ballast had the highest peak shear strength and the greatest resistance to deformation, both of which are related to particle shape. Additionally, the macroscopic friction coefficient (μ*) decreased as the proportion of used ballast increased, especially beyond 30%. At the microscale, a higher used ballast ratio resulted in more floating particles and a lower coordination number (Z). Furthermore, microscale findings indicate that maintaining key mechanical properties requires a lower used-ballast content than that suggested by macroscale results; based on the microscale indicators, 20% used ballast was identified as a suitable proportion. Preliminary large-scale triaxial tests showed that the peak stress response varied among the fresh–used ballast mixtures; therefore, the experimental results were interpreted alongside DEM-based macro–micro indicators. The F80U20 mixture provided a suitable balance between mechanical performance and reuse potential. Overall, this study supports the controlled reuse of used ballast in railways, emphasizing potential economic and environmental benefits. It promotes resource efficiency and encourages sustainable practices in civil engineering and railway maintenance.