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.

When performing railway track stiffness analyses, in current standards sleepers are often regarded as a rigid member. For flexible sleeper materials like timber or polymers, this may lead to underestimating rail deflections up to a factor two and overestimating rail seat loads up to 20%. Calculations incorporating sleeper bending can currently be performed analytically by a two-layer beam-on-elastic-foundation calculation, or by finite element analyses, but a simple approach does not yet exist. This article introduces a simple calculation method to establish rail deflections, track stiffness and rail seat loads, incorporating the effects of both bending and shear stiffness of the sleeper, applicable to new or tamped track. A sleeper flexibility factor f_S is introduced as a deformation multiplication factor compared with a rigid sleeper. Validation against current calculation models shows a deformation accuracy within 6% and a load accuracy within 2%. When a track is not maintained, a gap will develop under the sleeper at the rail seat. The size of this gap correlates to the stiffness of the sleeper. Eventually a uniform load distribution can develop under the sleeper. A calculation method is introduced to estimate the gap and the track behaviour at uniform load distribution. When for flexible sleepers the track deflection due to the gap can develop outside of the desired range, timely track maintenance or monitoring is advised.

In ballasted track, the wheel load is transmitted to the subgrade via sleepers commonly made of impregnated wood, prestressed concrete, steel or recently developed polymer sleepers. Mentioned material types of sleepers are characterized by different elastic moduli being a key parameter in any numerical model. Hence, this paper aims to determine the elastic modulus of sleepers subjected to a laboratory four-point bending test. Traffic resembling load level of 60 kN adopted from a typical axle load distributed by the rails to the sleeper was applied in a quasistatic and cyclic loading. The samples included sleepers made of polymers complemented with wood and pre-stressed concrete. The results of this paper are based on the elastic modulus investigation. Main conclusions are focused on the sleeper's elastic modulus under changing loading frequencies. Wood and prestressed concrete sleepers indicated mainly elastic behaviour resulting in a constant elastic modulus. However, polymer sleepers showed a loading frequency dependent elastic modulus as a result of their viscous elastic behaviour. Moreover, the conclusions of this paper involve E-modulus measurements of impregnated beech sleepers in order to describe their piece by piece elasticity variation due to their natural origin.