Keywords: ballasted track, unsupported sleeper, track stability, track irregularity, lateral axle force, management standard.

The design and management of ballasted track assume that the track panel is uniformly supported. As an actual situation, unsupported sleepers which are not supported on the ballast in the case where the train load does not act on them, are found sporadically at ballasted track. Unsupported sleepers are known to cause management problems such as loss of track buckling stability. In fact, continuous unsupported sleepers have been found to be present in all locations where track has been abnormally misaligned during high-temperature periods. In this study, a numerical analysis was performed on buckling stability, and the limit of lateral axle force to prevent shifting of track, in consideration of the actual situation of unsupported sleepers. As a result, it has become clear that the presence of unsupported sleepers increases track lateral displacement when the rail temperature increases, and that to ensure the lateral stability of the track at locations where unsupported sleepers exist, it is necessary to keep track lateral irregularity to a small level. Based on the results, management standards for unsupported sleepers and lateral track irregularity at high temperatures were established, and have been put into operation, and are proving effective.

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