Keywords: rail fastening system, bolt retightening, leaf spring, unsupported sleeper, washer, rail clamping force, fatigue failure, trial installation.

In this study, the authors aimed to develop a rail fastening system requiring no bolt retightening by identifying issues associated with a rail fastening system developed in a previous study. First, as a result of trial installation of the previously developed rail fastening system on the test track, the authors confirmed that, at locations with unsupported sleepers, washer insertion was not possible in some cases because the sleeper dropped onto the ballast. To resolve this issue, the authors proposed a fastening method in which the sleeper and bolt are lifted together by using the bolt head as a reaction force. This method secures sufficient clearance for washer insertion even at locations with unsupported sleepers. Based on this concept, the authors fabricated an improved rail fastening system and a fastening tool. Assembly tests confirmed that washers could be inserted even at unsupported sleeper locations. In addition, static and dynamic loading tests confirmed that the improved rail fastening system satisfies the safety requirements against fatigue failure. Finally, the authors conducted a trial installation on an operational line. Visual inspection after approximately three months confirmed that no abnormalities, such as bolt loosening or washer dislodgement, were observed.

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