4. Elastic Sleeper for Ballasted Track with Low Spring Constant

      For the purpose of reducing track maintenance and vibration, the Railway Technical Research Institute (RTRI) has developed an elastic sleeper that is softer (i.e. with a smaller spring constant) than the conventional one for ballasted track (Fig. 1). Repeated load tests were performed using one type of urethane rubber with increased foaming ratio and two types of double-layered vulcanized rubber (flat structure and grooved structure) (Fig. 2). The ballast settlement progress coefficient (settlement in mm for ten million tons) for the urethane rubber type and vulcanized rubber type (flat structure) was found to be outstanding, at about half that of the general ballasted track (PC sleeper type 3 track). The ballast settlement progress coefficient for the vulcanized rubber type (grooved structure) was about 2.4 times. Spring constants for the urethane and vulcanized rubber (flat structure) types, which showed good results in the above tests, were 1/10 and 1/3 of the ordinary elastic sleeper respectively, resulting in smaller spring constants.
      Motor trolley running tests were also carried out to investigate the vibration reduction effects of urethane rubber. The vibration level at a point 4.6 m from an elevated bridge was 3 dB lower (Fig. 3) than conventional elastic sleeper track (low expansion ratio urethane), which demonstrates a significant vibration reduction effect.

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