A realistic assessment of the whole life cost of rail track foundations requires analysis of the effects of the repeated loadings applied by trains. This paper reports the effects of principal stress rotation (PSR) during cyclic loading on the permanent deformations measured in a series of hollow cylinder tests. The tests were carried out on a number of reconstituted soils selected in order to simulate foundation materials on an existing heavy haul railway line. Typical loadings and track geometry together with dynamic finite-element analyses were used to define representative stress changes to be applied to these soils, which were then tested with and without principal stress rotation during loading. It is shown that principal stress rotation has a significant and deleterious impact on permanent deformation of some materials. Therefore, it is concluded that cyclic triaxial testing, which cannot impose principal stress rotation, will not necessarily give good estimates of the long-term performance of rail...

This paper presents the results of a detailed investigation into the ground deformations that occur under a railway line during the passage of a train. Four horizontal boreholes were installed at different depths below a ballasted railway track. Ground deformations were measured using geophones at set distances from the centreline of the track within each borehole. The results show vertical displacements reducing with depth, from a maximum at the sleeper. Sleeper displacements are dominated by pairs of bogies at the ends of adjacent wagons (which have a frequency of loading 1 Hz), although the effects of individual bogies (2 Hz) and axles (6 Hz) are also apparent. Higher loading frequencies attenuate with depth so that at a depth of 0·780 m below the sleeper soffit no axles are visible within the displacement data and by a depth of 1·98 m only the combined effect of pairs of adjacent bogies is apparent. In contrast, longitudinal horizontal motion is greatest at a depth of 0·78 m below the sleeper soffit, and the longitudinal horizontal displacements at the sleeper and at a depth of 0·78 m are dominated by the individual axles (∼6 Hz). By a depth of 1·98 m, the longitudinal horizontal motion is dominated by the bogie pairs. A dynamic linear-elastic two-dimensional finite element model was developed and validated using the measured displacements.

The design of a railway track substructure requires a realistic understanding of the resilient behavior of the underlying track foundation materials, namely, the subballast and subgrade layers. Currently, the best available method of characterizing the resilient behavior of track foundation materials is through the execution of cyclic triaxial tests, although these do not have the ability to impose principal stress rotation (PSR) on test specimens. A previous paper by the authors demonstrated that PSR increases the rate of permanent strain development. This paper reports on the effects of PSR on the resilient behavior of track foundation materials. Four different reconstituted soils selected to represent typical track foundation materials were subjected to undrained cyclic and torsional shear tests in a hollow-cylinder apparatus. It was established that PSR reduces the resilient modulus of the materials compared with cyclic loading without PSR. The effects of PSR as a function of clay content, overconsolidation ratio (OCR), and consolidation regime (isotropic or anisotropic) were also investigated.http://ascelibrary.org/loi/jggefkhb201

As train speeds and heavy haul axle loads constantly increase due to market demands, so do the stresses and strains experienced by track structures. This is especially true for track transitions that generate high dynamic forces on both the track and vehicles because of poor vertical track geometry and/or differing track stiffness values on either side of the track transition. Reducing differential settlement between the two track structures at a track transition is one method of improving the life of the track, and increasing maintenance intervals. In this study, rigid polyurethane foam was used to reinforce ballast. Tests were conducted using a dynamic hydraulic load frame and a single sleeper in a large ballast box subjected to heavy haul axle loads. Unreinforced, reinforced and 50% reinforced ballast layers of 300 mm depth were tested to approximately 5 000 000 load cycles. The results showed that rigid polyurethane foam-reinforced ballast exhibited in the order of 60% less settlement for a fully reinforced layer, and 42% less settlement for a half reinforced layer. The use of rigid polyurethane foam (RPF) to reinforce ballast has a number of benefits that could result in better track geometry and longer maintenance cycles, in turn resulting in lower life cycle costs. Keywords: ballast, concrete sleepers, ballast settlement, ballast breakdown, rigid polyurethane foam, cyclic loading

Under-sleeper pads (USPs), typically made from polyurethane, are used by railways in certain parts of the world to reduce ballast settlement and consequently lengthen the ballast tamping cycle. The rationale behind this relatively new addition to the conventional ballasted track structure is that the pad increases the contact area between the angular ballast particles and the underside of the concrete sleeper, with the effect that ballast breakdown and total track settlement are reduced. This paper describes two experiments on the effects of USPs on four aspects of sleeper-ballast interaction, namely contact area, contact pressure, ballast settlement and ballast breakdown. Static and dynamic tests up to 1 million loading cycles were performed under controlled laboratory conditions on concrete sleepers with and without USPs. Sophisticated pressure sensors revealed an increase in contact area from 12% to 35% for static loading tests, and from 8% to 20% for dynamic tests, with a resulting 70% reduction in contact pressure. In addition, a 44% reduction in ballast settlement and a 23% reduction in ballast breakdown were achieved by the introduction of USPs. In conclusion it is argued that the introduction of USPs specifically on heavy-haul lines would offer significant advantages with respect to ballast settlement and breakdown. These advantages are most likely to lengthen general ballast tamping and screening cycles, resulting in significant life cycle cost savings. Keywords: under-sleeper pads, ballast, concrete sleepers, ballast settlement, ballast breakdown