Improved lateral resistance test: investigating the effect of a partial uplift restraint during a single sleeper push test

Conventional railway sleeper (tie) lateral resistance tests often assess small lateral displacements (∼2 mm) and do not consider the vertical displacement (uplift) of sleepers through lateral plane rotation which, for installed sleepers, is constrained by the supported rail. Consequently, unrestrained tests tend to underpredict the lateral resistance achievable in service. This paper describes an alternative single sleeper push test (SSPT) methodology in which railway sleepers are restrained during laboratory lateral resistance tests, with a passive restraint system used to limit sleeper uplift. The lateral resistance of concrete and steel sleepers has been investigated using a SSPT in a ballast box with and without the use of the new restraint system. It has been found that, when unconstrained, both concrete and steel sleepers uplift, with the greatest uplift values seen for steel sleepers. In the more realistic restrained configuration, the lateral resistance of the concrete sleeper increased. The steel sleeper saw an even greater increase in lateral resistance and furthermore experienced a rising lateral resistance with increasing lateral displacements. An existing model was used, and expanded, to predict the buckling stability of track for both restraint conditions, with significantly lower minimum buckling temperatures found for both sleeper types when free to uplift. This study shows that partial restraint of sleepers, as imposed by the rail in track, has a tangible influence on the sleeper lateral resistance during push tests compared with unrestrained tests. The results of this study enhance the understanding of sleeper behavior during lateral track shifts, which has the potential to improve buckling risk mitigation strategies.