It is well established that a stiff sub-ballast layer will increase the durability of track geometry over time. However, Network Rail does not tend to specify a minimum modulus of deformation that aligns with other European Infrastructure Managers practice, in terms of formation treatment and when to implement an engineered design. Therefore, Network Rail tend to either leave it alone or lay a sand blanket due to drainage issues, which may not improve the performance. This has been particularly relevant in instances such as track lowering under bridges. The aim here is to reduce the kinematic envelope of the new overhead lines for the train and the track to pass under an existing road bridge rather than reconstruct a new one. The key premise is that the more material Network Rail need to excavate and then relay, the more expensive and time consuming the work.
The research will encompass a mixture of field trials, lab and railway track work, which will look at measuring the different stiffness/deformation of existing subgrades, propose a value(s) below which strengthening is required and when to undertake it, and finally propose an efficient and cost-effective sub-ballast ballast layer in terms of material specification, layer thickness, compaction methodology.
Linked to the approach above, it would also enhance the durability of the track geometry and therefore lead to a reduction in maintenance time and costs. This would lead ideally to developing a specification for a sub-ballast layer that can be installed; as well as some kind of compacted granular fill to reduce the thickness of the sub-ballast layer – as cost-efficiency savings could be made. The outcomes of this would also contribute to Network Rail writing highly efficient specifications for sub-ballast capping, which in turn, would provide guidance on when – or when not – to use it.
The project is supported by Network Rail and therefore will provide opportunities to work closely with industry. Considering the potentially high international impact of the research, the candidate should be comfortable with travelling to international conferences to present their work as appropriate.