The sleeper to ballast interface plays a crucial role in the stability of ballasted railway track, transferring both vertical and lateral loads safely from the superstructure to the sub-base. However, current conceptual models for the behaviour of the interface are incomplete and too simplistic to assess the response of the track system to the loads exerted by modern trains. For example, the increased curving speeds associated with tilting trains introduce potentially significant combinations of vertical, lateral, and moment loading which are not explicitly considered in current assessment procedures. Also, the relative contributions of the base, crib, and shoulder ballast to lateral sliding resistance are at present poorly quantified. The behaviour of the sleeper to ballast interface was investigated in a series of tests in an apparatus capable of applying combinations of load representative of real trains. This article presents test data quantifying the relative contributions to total sliding resistance of the base, crib, and shoulder. New calculations are presented, which enable the resistance from the crib and various sizes of shoulder ballast to be quantified. The results of the experiments and calculations are compared with each other and with the literature, and reasonably consistent patterns of behaviour are identified.

The performance of switches and crossings compared with plain line is complicated by the presence of movable parts, changing rail geometry and non-uniformities in the composite and/or trackbed stiffness. These features lead to complex vehicle–track interactions and higher maintenance costs. The trackbed stiffness is the least well-controlled engineering property. A greater variability in trackbed stiffness leads to higher differential trackbed settlement and associated poorer track quality. At switches and crossings, changes in trackbed stiffness are exacerbated by changing rail properties which also contribute to changes in the overall composite track stiffness. This work focuses on the role of variations in stiffness on the performance of switches and crossings. Field measurements of bearer displacement were carried out using geophones at a switch and crossing equipped with under sleeper pads. The vehicle–switch and crossing interaction was modelled using a multi-body system and finite element method. The trackbed stiffness along the whole of the switch and crossing was inferred using the measurements of track deflections in an iterative back-calculation taking account of changing rail properties. It is shown that not including the variation in trackbed/composite stiffness leads to significant under/overestimates of the wheel–rail contact forces. Under sleeper pads are shown to reduce absolute maximum loads, but may increase the variation in deflection.