Unsupported sleepers, which are found sporadically along railway ballasted track, cause various problems from track geometry management, such as a rapid deterioration of the track condition. In this study, we conducted on-site measurement of the response in commercial line and a follow-up survey of the amount of the gap between the bottom of the sleeper and upper surface of ballast (gap value). As a result, it is confirmed that the rail seat load is smaller and the vertical displacement of the sleeper is larger at the sites of unsupported sleepers than at the normal ones; the phenomenon can be reproduced by numerical calculation; the unsupported sleeper location is almost predictable, and the gap value gradually increases and affects the progress of longitudinal level irregularity.
