TRACK SYSTEMS FOR HIGH SPEED RAILWAYS: GETTING IT RIGHT

Lead Research Organisation: University of Birmingham
Department Name: Civil Engineering

Abstract

Train speeds have steadily increased over time through advances in technology and the proposed second UK high speed railway line (HS2) will likely be designed with "passive provision" for future running at 400 km/hour. This is faster than on any ballasted track railway in the world. It is currently simply not known whether railway track for speeds of potentially 400 km/hour would be better constructed using a traditional ballast bed, a more highly engineered trackform such as a slabtrack or a hybrid between the two. Although slabtrack may have the advantage of greater permanence, ballasted track costs less to construct and if the need for ongoing maintenance can be overcome or reduced, may offer whole-life cost and carbon benefits. Certain knowledge gaps relating to ballasted track have become apparent from operational experience with HS1 and in the outline design of HS2. These concern
1. Track Geometry: experience on HS1 (London to the Channel Tunnel) is that certain sections of track, such as transition zones (between ballasted track and a more highly engineered trackform as used in tunnels and on bridges) and some curves require excessive tamping. This results in accelerated ballast degradation and increased ground vibration; both have an adverse effect on the environmental performance of the railway in terms of material use and impact on the surroundings. Thus the suitability of current design rules in terms of allowable combinations of speed, vertical and horizontal curve radius, and how these affect the need for ongoing maintenance to retain ride quality and passenger comfort is uncertain.
2. Critical velocity: on soft ground, train speeds can approach or exceed the speed of waves in the ground giving rise to resonance type effects and increased deformations. Instances of this phenomenon have been overcome using a number of mitigation measures such as the rebuilding of the embankment using compacted fill and geogrids, installation of a piled raft and ground treatment using either deep dry soil mixing or controlled modulus columns. The cost of such remedial measures can be very high, especially if they are taken primarily on a precautionary basis. However, many methods of analysis are unrefined (for example, linear elastic behaviour is often assumed or the heterogeneity of the ground, track support system and train dynamics are neglected), and conventional empirical methods may significantly overestimate dynamic amplification effects. Thus there is scope for achieving considerable economic benefits through the specification of more cost effective solutions, if the fundamental science can be better understood.
3. Ballast flight, ie the potential for ballast particles to become airborne during the passage of a very high speed train. This can cause extensive damage to the undersides of trains, and to the rails themselves if a small particle of ballast comes to rest on the rail and is then crushed. Investigations have shown that ballast flight depends on a combination of both mechanical and aerodynamic forces, and is therefore related to both train operating conditions and track layouts, but the exact conditions that give rise to it are not fully understood.
The research idea is that, by understanding the underlying science associated with high speed railways and implementing it through appropriate, reasoned advances in engineering design, we can vastly improve on the effectiveness and reduce maintenance needs of ballasted railway track for line speeds up to at least 400 km/h.

Publications

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Soper D (2017) A comparative study of methods to simulate aerodynamic flow beneath a high-speed train in Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit

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Soper D (2017) Full scale measurements of train underbody flows and track forces in Journal of Wind Engineering and Industrial Aerodynamics

 
Description The aspect of the overall project studied by the Birmingham team was the flight of ballast under high speed trains, and the key findings below refer to this work only, rather than the work of the wider (Southampton University led) project.
1. The full scale measurements of flow velocity and pressure beneath trains, coupled with measurements of track displacement and ballast acceleration by Southampton University have revealed the complex nature of the forces on ballast particles during the passage of trains. In particular initial analysis of the results suggests that accelerations due to the passage of trains are much larger than those induced by aerodynamic effects.
2. The use of moving model tests and CFD analysis to measure the flow velocities and pressures beneath trains shows a high level of agreement with the full scale data and offers possible way forward for train homologation.
Exploitation Route The use of moving model tests in particular could be taken forward as a testing method for the measurement of train underbody flows.
Sectors Construction,Environment,Transport

 
Description The project provided a wealth of information on the nature of the flow beneath trains, and the interaction between aerodynamic and mechanical effects on ballast flight. This has led to the first coherent model of ballast movement between trains that takes into account both effects. This model has been used as the overarching framework for the chapter on ballast flight in the recent text book "Train Aerodynamics: Principles and applications". Some of the data that has been obtained is being used in the ongoing development of the CEN standard in this area. In addition the underbody flow data has been used to validate a novel physical moving modelling techniques where upside trains pass beneath a suspended ground plane. This technique has much promise for train validation studies.
First Year Of Impact 2018
Sector Environment,Transport
Impact Types Societal,Economic,Policy & public services

 
Description Southampton 
Organisation University of Southampton
Department Faculty of Engineering and the Environment
Country United Kingdom 
Sector Academic/University 
PI Contribution The project was a joint collaboration between University of Birmingham and University of Southampton. This was the first collaboration between the PI and University of Southampton.
Collaborator Contribution University of Southampton was responsible for the Geo-technical aspects of the project while University of Birmingham was responsible for the train aerodynamic part. University of Southampton used the aerodynamic data generated by Birmingham for the flow around trains to investigate the movements of the ballast underneath the train.
Impact Soper, D., Flynn, D., Baker, C., Jackson, A. & Hemida, H. (2017) "A comparison of methods to simulate the aerodynamic flow beneath a high speed train" In : Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. 44 p.1-19
Start Year 2016
 
Description Eureca Conference, Malaysia 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact That was an invited keynote speech in Taylor University annual conference in Malaysia.
Year(s) Of Engagement Activity 2016
 
Description Keynote London 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact This was an invited keynote speech in the The Global Summit and Expo on Fluid Dynamics and Aerodynamics.
Year(s) Of Engagement Activity 2016
 
Description Keynote lecture - Train aerodynamics, past, present and future 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Keynote lecture, Railways 2016, Cagliari, Sardinia
Year(s) Of Engagement Activity 2016
 
Description Organizing International conference 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact University of Birmingham has been chosen to host the 9th International Conference of Bluff Body Aerodynamics and Applications (BBAA), Birmingham, 2020. Hemida is the Chair of the conference.
Year(s) Of Engagement Activity 2018
 
Description Talk to HS1 staff on research project 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Followed byanimateddiscussion on the research work

HS1 agreed toast as partner of further grant applications
Year(s) Of Engagement Activity 2015
 
Description Visiting Professor 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact Dr Hemida was invited as a visiting professor at the Lanzhou university in China to deliver three lectures about train aerodynamics as part of their 60th anniversary of train aerodynamic division in the university. The audiences were a mix of academics, graduate and undergraduate students. The number of attendees was about 200.
Year(s) Of Engagement Activity 2018