Correlating ballast stiffness/settlement and sub-ballast behaviour with trackbed performance and maintenance needs

In laboratory experiments and field monitoring of railway tracks, we tend to focus on the elastic (in cycle) stiffness and the accumulation of plastic (permanent) settlements over millions of loading cycles. However in reality, it is the development of differential settlements and lateral movements that drive maintenance needs. Variations in track level are characterised by the standard deviation (from the smooth ideal) over typically a 35 m wave length. The challenge is to link the measureable and quantifiable parameters of elastic stiffness and the development of permanent settlement to these from the often seemingly random deviation of the track from the desired line and level. The project will start with a review and critical appraisal of current approaches and models for the prediction of ongoing track geometry deterioration, which are largely empirical and based on relatively little data. Data obtained from T2F field study sites will be used to develop new correlations, back-referenced to the laboratory sleeper testing rig data generated by others. Modelling using 3D dynamic finite element analyses incorporating soil models able to reproduce the accumulation of plastic settlement with cyclic load, controlled spatial variability in the sub-base (soil or ballast thickness, stiffness and type) and initial defects that attract loading anomalies, will then be carried out to investigate the forms and magnitudes of variability leading to geometry deterioration as quantified by the development of standard deviation. The applicability of a stochastic approach will also be investigated. The new findings will be used to improve current approaches or develop new ones, which will then be incorporated into integrated T2F models for improved track performance prediction and maintenance planning.

The ’Correlating ballast stiffness/settlement and sub-ballast behaviour with trackbed performance and maintenance needs’ project is part TRACK TO THE FUTURE (T2F) a major five-year, £8M research programme, funded by EPSRC, industry and the Universities of Southampton, Birmingham, Huddersfield and Nottingham. Its aim and vision is to support the development of railway track systems that are efficient in terms of embodied carbon, materials use and cost; robust in requiring little maintenance; and unintrusive in producing little noise. It will address this aim through three interlinked Research Challenges RC.

TRACK4LIFE (RC1): low-maintenance, long-life track systems with optimised material use, through
• developing, and demonstrating the effectiveness of, new track forms or components and promising interventions e.g. under-sleeper pads and random fibre ballast reinforcement (1A)
• developing an understanding of the relationships between the key measurable parameters of track stiffness and track settlement, and the key performance parameter of geometrical standard deviation, taking into account the interactions with rail geometry and vehicle dynamics (1B), and
• extending the life of ballast by reducing or eliminating the factors leading to its degradation, assessing the feasibility of design for the degraded state and facilitating re-use rather than downcycling or disposal (1C).

DESIGNER CROSSINGS AND TRANSITIONS (RC2): crossings and transitions that optimise the behaviour of the vehicles traversing them, thereby minimising damage. This will be achieved by developing new understandings of the highly complex interactions between switch and crossing geometry, sub-base support, wheel profile and vehicle dynamics, including the effects of varying the support stiffness through the crossing or transition; and combining them with the potential of modern manufacturing methods to provide a tuned variation in geometry and materials properties.

NOISE-LESS TRACK (RC3): an integrated approach to designing a low-noise, low-vibration track consistent with reduced whole life costs and maintenance needs. Track is the main source of railway rolling noise and has a key role in vibration transmission into the ground. Noise is increasingly cited as the main objection to the expansion, reopening or construction of railways. However, design changes are usually driven by other concerns with the implications for noise and vibration considered as secondary effects.

Applications for this PhD research project are accepted on a rolling basis and we therefore advise you to apply early if you are interested. To make your application please go to: http://www.southampton.ac.uk/engineering/postgraduate/research_degrees/apply.page

If you wish to discuss any details of the project informally, please contact Professor William Powrie, Infrastructure research group, Email: [Email Address Removed], Tel: +44 (0) 2380 59 3214.

This project is being run in participation with the EPSRC Centre for Doctoral Training in Sustainable Infrastructure Systems (http://www.cdt-sis.soton.ac.uk/). For details of our 4 Year PhD programme and further projects, please see http://www.findaphd.com/search/PhdDetails.aspx?CAID=2477

Visit our Postgraduate Research Opportunities Afternoon to find out more about Postgraduate Research study within the Faculty of Engineering and the Environment: http://www.southampton.ac.uk/engineering/news/events/2016/02/03-discover-your-future.page