This research investigates the natural vibration characteristics of the ballast layer by using field measurement, full-scale experiments and large-scale finite element analysis. The results indicate that the natural frequency of the vertical elastic vibration of the ballast layer is numerically detected at around 310 Hz at which the whole ballast aggregate repeats the vertical expansion and shrinkage elastically, and that the rigid-body natural vibration numerically occurs approximately at 120 Hz at which the mass of the track structure vibrates simultaneously up and down as depending on the stiffness of the ballast layer. The stress acting on an angularity part of the ballast gravel is inferred to be about 1100 times greater than the average stress on the bottom surface of the sleepers
