Discrete element modeling of ballast settlement under trains moving at “Critical Speeds”

The majority of US high speed trains will operate on the current ballasted track network. It is suspected that the change in loading characteristics especially when trains move at so called “Critical Speeds” may cause unfavorable track performances, for instance increase in track settlement (both in ballast and the subgrade soil). Effort has been taken in this research to investigate the impact of load patterns generated by high speed trains on the track settlement accumulation. A dynamic track model consists of rail-tie-ballast “Sandwich” upper structure, and a finite 3D soil substructure model is developed and utilized to obtain the loading pulses and pulse combinations introduced by different traffic patterns on the top of the ballast layer. An Image Aided Discrete Element Modeling approach is then employed to simulate the ballast settlement under those realistic loading pulses and pulse combinations. Results and conclusions will be highlighted and recommendations will be made in the end.