The progress mechanism of track geometrical irregularity focusing on hanging sleepers

This topic is very traditional and basically has been concerned for a long time. A lot of sophisticated vehicle/track interaction model and track dynamic deterioration model have been developed so far. The author also developed a track settlement progress model comprising a vehicle/track interaction model and a track settlement law. Hanging sleepers are usually caused more or less by the dynamic effect of vehicle/track interaction and has a great impact on the progress of geometrical irregularity of longitudinal track profile. This paper describes that the long term, for seven years, monitoring of track deterioration focusing on actual rail welds and short term monitoring, for three weeks, and dynamic measurements excited by track irregularities set up artificially under the combination with rail surface irregularity considering the typical longitudinal profile of rail welds and track geometrical irregularity considering the typical longitudinal profile of dip joints. Plenty of parameters have influence on the long term monitoring of track settlements and the dynamic measurements of track behaviour, but in this study hanging sleeper was focused on as a key parameter of progressing track geometrical irregularity. Based on the achievements of long term monitoring of track settlements and the dynamic measurements of track behaviour with the focus on rail and/or sleeper displacement and rail bending stress, the impact of hanging sleepers on the geometrical irregularity growth mechanism of track longitudinal profile was discussed and identified to be significant. In addition, the adequacy of track settlement prediction model proposed in this paper was verified to some extent in spite of limited monitoring and measurement conditions.