Effect of tamping operation on mechanical qualities of ballast bed based on DEM-MBD coupling method

Tamping can effectively improve the service performance of a ballasted track. To determine the effect of tamping on the mechanical qualities of a ballast bed, a tamp-sleeper-ballasts coupling model was established based on the coupling of the discrete element method (DEM) and multibody dynamics (MBD). This model not only solved the problem that the interaction between ballasts and sleeper could not be revealed accurately by DEM, but also realized the complicated motion simulation of tamp. The model was subsequently verified by field tests. Finally, we applied the model to analyze the macro-mesoscopic motion of ballasts, as well as the effects of tamping parameters on the mechanical qualities of ballast bed. The results show that tamping destroys the uniformity of ballast bed, and the top layer under sleeper and the crib are the most severely affected spaces, whose compactness increased by 7.56% and decreased by 34.77%, respectively. In terms of the analytical results for compactness, lateral resistance, and support rigidity, the recommended lifting height, tamping frequency, and tamping depth are 20 mm, 35 Hz, and 20 mm, respectively. This study can provide critical insights for the improvement of tamping operation.