Effect of tamping duration on mechanical properties of ballast beds: a DEM-MBD coupled investigation

As a critical maintenance method for ballasted tracks, tamping operations effectively improve ballast bed compactness and mechanical performance. Tamping duration critically influences the mechanical response of the ballast bed, yet systematic studies on the relationship between the duration of tamping and the mechanical performance of ballasted tracks are lacking. In this study, we established a discrete element method-multibody dynamics (DEM-MBD) coupled model of tamping machinery and a ballasted track to systematically analyze the effects of tamping duration on ballast bed compactness, particle motion, and ballast contact behavior. The results show that increasing the tamping duration enhances the compactness beneath sleepers and the uniformity of compactness in the ballast bed. Tamping duration significantly affects ballast motion. A prolonged tamping duration significantly decelerates ballast particle movement beneath sleepers, particularly during the inserting stage, while in the squeezing stage, it exhibits a smaller decrease. The inter-sleeper region is particularly sensitive to tamping duration variation, showing substantial velocity reductions in ballast particles during both the inserting and lifting stages. Increased tamping duration rapidly decreases contact forces in ballast particles during the inserting stage, stabilizes contact forces in the squeezing stage, and elevates the coordination number among ballast particles. The squeezing stage exhibits the most significant mechanical energy fluctuations, while the evolution patterns of translational and rotational kinetic energies show strong correlations with ballast motion characteristics. Appropriately increasing the tamping duration enhances the overall mechanical performance of the ballast bed and extends track maintenance cycles. This study revealed the mechanism underlying the effects of tamping duration on the mechanical behavior of ballast beds, providing a theoretical foundation for the precise design of tamping parameters.