Differential Settlement Prediction of Ballasted Tracks in Bridge-Embankment Transition Zones

Track degradation and defects of existing passenger and freight mixed railroads are concentrated in bridge-embankment transition zones. Heavy axle load (HAL) operation on existing railroads presents a complexity in evaluating the evolution of the differential settlement of the overloaded ballasted track, especially in bridge-embankment transition zones. In this paper, an iterative prediction methodology of track differential settlement in transition zones is developed. In this methodology, the history of the loading on the ballast and the history of the loading on the subgrade are considered as well as the vehicle-track interactions. The sleeper-ballast contact forces and the subgrade soil deviator stress field change with iterations. A case study was analyzed to investigate the track differential settlement in a bridge-embankment transition zone of an overloaded passenger and freight mixed line. The distribution of the sleeper-ballast contact forces along the track and the distribution of the subgrade soil deviator stress were calculated with a vehicle-track-subgrade model. Results indicate that the critical axle load of the vehicle for existing ballasted track transition zones without any reinforcement treatment is 27 t. Because HAL vehicles may have axle loads up to 39 t, the increase of the train axle load, reinforcement treatments, and remediations are required for existing transition zones. The maintenance scheduling for tracks under different axle loads was calculated.