Research on the dynamic behaviour of the railway ballast assembly subject to the low loading condition based on a tridimensional DEM-FDM coupled approach
To gain insight into how dynamic energy transmits within the ballasted assembly, a three-dimensional coupled model that accounts for both the discrete element method (DEM) and the finite difference method (FDM) was established in this paper. The ballast particles were simulated by the DEM, in which the rolling resistance model was considered, and interface elements were used to fulfil the coupling process between the DEM and the FDM. In addition, an in situ test was performed to verify the numerical model under the impact load. The results show that, during the static process, both the shape of the sleeper and the confinement of the subgrade surface had a significant effect on the force chains structure within the ballast assembly. Furthermore, when an impact load was applied, the force chains changed negligibly. Considering the deformation field within the assembly, near the subgrade surface, the root mean square (RMS) distribution of the ballast particles conformed to the force chains structure. Considering the stress field within the assembly, the vertical dynamic stress concentrated beneath the sleeper and the shear dynamic stress covered near the subgrade surface. They both transmitted through the force chains that were formed in the ballast assembly, through which the shear dynamic stress distributed more widely. Therefore, it can be concluded that the force chains within the ballast assembly are closely related to the shape of the sleeper, and this also has a significant influence on the path of the energy propagation within the ballast track.
Keywords: Ballasted track, Dynamic behaviour, DEM-FDM coupled model, Rolling resistance model,