ABSTRACT
Dynamic vehicle/track forces from a train travelling over a long continuous wave in vertical track profile can compress the ballast preferentially in the troughs, thus making the wave worse. This model, built from simple representations of ballast, track and vehicle response, provides qualitative insights into the physical phenomena involved. This chapter explores the physical processes by developing a model of the complete process by which vehicle bounce can cause an existing continuous wave in track vertical profile to grow in amplitude as successive vehicles pass by. The model shows how dynamic forces from a train travelling over a continuous preexisting long wave in vertical track profile compress the ballast preferentially in the troughs, thus making the wave worse. Predicted rates of deterioration are sensitive to parameters in the ballast model. Strong dynamic response from a vehicle running on compressible ballast is predicted to ruin newly tamped track in one train pass.
