A Self-Levelling railway sleeper concept and its large-scale testing

Railway track transition zones present engineering challenges due to their abrupt change in stiffness between structural elements such as embankments, bridges and tunnels affecting track geometry parameters. Although a variety of stiffness-based remedial measures have been widely applied, their implementation can be constrained by high capital cost, operational disruption, and the complexities associated with modifying the substructure. As a result, interventions in practice commonly focus on controlling permanent deformations and differential settlement, particularly related to the development of hanging sleepers. Thus, this study investigates the use of modular self-levelling sleepers (SLS) as a solution. To do so, two concept SLS systems are designed and developed: one employing a granular mechanism (SLS-G), and the other based on a horizontally acting wedge mechanism (SLS-HW). Both variants use the polymeric sleepers and are designed for compatibility with conventional ballasted track systems. Experimental laboratory testing is undertaken, and it is found that the SLS prototypes were able to restore the sleeper-ballast contact for voids up to 40 mm depth, while stress measurements at the interface indicated improved load distribution under the rails. The findings support the proof-of-concept that self-levelling sleepers have the potential to be a modular, low-disruption solution for mitigating track geometry degradation and reducing maintenance requirements at transition zones.