Effects of differential subgrade settlement on slab track deformation based on a DEM-FDM coupled approach

Slab track structures become deformed under the effects of differential subgrade settlement. According to the properties of the China Railway Track System (CRTS) II slab track on a subgrade, a three-dimensional (3D) coupled model based on both the discrete element method (DEM) and finite difference method (FDM) was developed. The slab track and subgrade were simulated using the FDM and DEM, respectively. The coupled model was verified. The deformation of the slab track and contact forces of gravel grains in the surface layer of the subgrade were studied under differential subgrade settlement. The effects of settlement wavelength, settlement amplitude, and other types of settlements were also discussed. The results demonstrate that the settlement amplitude and settlement wavelength of the subgrade have significant effects on track deformation. The deformation amplitude of the slab track increases nonlinearly with an increasing settlement amplitude of the subgrade. Increases in the settlement wavelength and amplitude of the subgrade significantly increase the maximum value of the contact force of the gravel grains in the subgrade. The maximum contact force of gravel grains near the boundaries of the settlement section can reach two to three times that of the unsettled condition, which makes it easy to accelerate the plastic settlement of the subgrade.