Keywords: ballast layer, void zones, DEM simulation, hanging sleeper, impact interaction, settlement intensity.

This paper presents an approach for simulation of the dynamic interaction of the sleeper and ballast in void zones, and the long-term processes of the settlement accumulation. A DEM model of a ballast box and one sleeper with spring support was developed to reflect the influence of the rails in the void zone. The model allows to simulate the void development as well as the void control. The ballast model was prepared to produce the results useful for long-term prediction. Additionally, an approach is proposed to accelerate the simulation time by using parallel simulations with different controlled initial voids. The simulation results indicate quick settlement accumulation after appearing of a void. Analysis of the dynamic interaction explains the reasons for the settlement acceleration: the impact loading and vibration that appears while void closing. The dynamic processes correspond to the experimentally measured ones: impact interaction appears in time before the maximal cyclic loading. The impact loading increases while the void growth, but the cycling loading decreases due to the loading transfer in the spring support. It results in a void of 5-6mm with the maximal settlement intensity where the amplitudes of the dynamic and the cyclic loadings are about the same level. The further increase of the void decreases the intensity. The results indicate that the impact loading is absolutely dominating in the settlement accumulating. The study results could improve the present ballast settlements' phenomenological equations to take into account the impact and vibration effects.

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