Effect of ballast pockets and geogrid reinforcement on ballasted track: Numerical analysis

The presence of ballast pockets in ballast track on soil subgrade is a common problem that significantly reduces the mechanical properties and durability of both the ballast bed and subgrade. However, insufficient research has been conducted on the impact and mechanism of these ballast pockets. In this paper, a numerical model of a ballast-subgrade test box based on the DEM-FDM coupling method is established, and the simulation results are verified by comparing them with the indoor test results. The specific effects of ballast pockets on the mechanical properties of the track bed and subgrade are discussed by simulating the ballast pocket development process by presetting various volumes. Furthermore, the effects of preventing and controlling ballast pockets are analyzed. The results indicate that settlement in the ballast bed mainly occurs during the initial stage of load action before leveling off. The total settlement S value is linearly related to the volume of ballast pockets, and linear fitting equations are established. The damage to the subgrade surface is mainly due to the stress concentration of the ballast exceeding the strength limit. Geogrid reinforcement helps reduce settlement in the ballast bed caused by ballast pockets; while also preventing intrusion the subgrade, and reducing the maximum stress on the subgrade surface. Compared with GG6 (geogrid with 6 cm apertures), GG4 performs better in preventing the formation of ballast pockets at the interface between the ballast bed and soil subgrade. Therefore, it is recommended to use geogrids with 4 cm apertures at this interface in the ballasted track.