Resilient rail infrastructure: dissipation driven fracture analysis of concrete support systems

The UK's rail infrastructure currently supports 1.3 billion passenger journeys and 100 million tonnes of freight each year. The freight transport alone contributes £870 million to the UK economy. The sector has seen 40% and 60% increases in passengers and freight over the last 10 years, respectively, and it is expected that passenger numbers will double and freight increase by 140% over the next 30 years. As the network has developed the magnitude and frequency of loads applied to the rail support systems have increased significantly, even over the last 10 years. It is estimated that between 2009 and 2014, the UK's rail operator, Network Rail (NR), will invest £3.75bn in track to maintain the network. The vast majority of this 32,000km of rail infrastructure is supported by pre-stressed concrete sleepers (PCSs) and crossing bearers (CBs). These concrete members provide lateral restraint and vertical support to the running steel rails. The PCSs and CBs are in turn supported on three sides by track ballast; crushed stone 30-50mm in diameter. Since their introduction in the 1950s, PCSs have superseded traditional wooden sleepers in new track and NR replaces approximately 200,000 timber sleepers each year with PCSs. However, despite the reliance of the UK's rail network on these concrete structures, and the simplicity of their geometry, surprisingly their structural behaviour is poorly understood. NR's CP5 delivery plan estimated that the used life of the sleepers supporting the network for the 2013/14 period is 60.9% and that 5,918 track failures would occur during the same timeframe. There are concerns that the development of fractures in concrete supporting members is undermining the rail network. In order to maintain a safe, reliable and resilient rail network it is essential to understand how the concrete support systems can be designed to future proof them against ever increasing structural demands.

The proposed research is concerned with three-dimensional dynamic analysis to assess the structural robustness of PCSs and CBs using a novel computational mechanics framework and associated numerical analysis technique. If successful, this research will provide a transformative, complete and consistent framework for modelling fracture in a variety of engineering materials. The creativity of this proposal lies in the application of up-to-the-minute ideas in constitutive modelling, fracture mechanics and numerical analysis techniques to a poorly understood yet critical component of the UK's rail infrastructure. It will provide a framework within which to develop new resilient rail-support system fastening methods.

This research will provide a new fracture simulation approach. It will also provide a framework within which to develop new resilient rail-support system fastening methods. Existing links between the PI and the UK's only pre-stressed concrete sleeper (PCS) and crossing bearer (CB) manufacturer will provide a pathway for this research to impact on the development of rail infrastructure. This impact can be split into a number of areas, namely:
(i) development of robust and resilient PCS/CB-rail securement methods;
(ii) safer railways and increased service performance;
(iii) reduction of produced C02 and operational costs through increased service life; and
(iv) understanding of the impact of higher speed (such as HS2) and load traffic on the existing ageing infrastructure (that is, will the sleepers fail through fracture).

The proposed research will bring together, currently separate, ideas within computational mechanics within a new analysis framework and could subsequently be applied to a number of other areas outside of the scope of this project.

The project will also develop the skills of a Post-Doctoral Research Assistant in constitutive modelling, fracture prediction and in computational modelling.