The Settlement Characteristics of Ballast Bed Based on Variable Boundary Ballast Box

The cumulative settlement of ballast bed greatly affects the service performance of railway lines. A discrete element method (DEM) model of ballast box with variable longitudinal force and accurate ballast shape was established in this study. The parameters of the simulation model were calibrated and validated by the self-developed experimental equipment of ballast box. Based on the validated DEM model, the mesoscopic effects of load frequency, load amplitude and longitudinal force of ballast bed on the settlement characteristics of ballast bed under cyclic loading were studied. The results show that the cumulative settlement of ballast bed includes initial settlement stage and stable settlement stage. The influence of longitudinal force on the settlement of ballast bed could not be neglected. The settlement decreases with the increase in the longitudinal force. When the longitudinal force increases from 5 to 8 kN, the settlement of ballast bed decreases by 68.2%. Besides, the settlement of ballast bed increases nonlinearly with the increase in load amplitude and frequency. When they increase from 60 to 80 kN and 32 Hz to 56 Hz, the settlement increases by 83.2% and 28.2%, respectively.