HIGH-SPEED RAIL
HS2
Ltd’s Andrew Went was among the
speakers at the recent
at the University of Birmingham, alongside University.
Went discussed some of the issues that designers, constructors and maintainers of high-speed track must consider – starting with the track velocities and the geodynamics, then because once you put this track system in place, it has to last 60 to 120 years,” Went said. “Good vehicle dynamic behaviour leads to better passenger comfort. I call that the ‘tea drinking factor’: can you sit in a railway carriage at a high speed and not lose your beverage over your lap?
“Low dynamic forces lead to reduced
to have a track system in place that, when it’s built, you’ve got to keep going back every week or month to keep maintaining it – you the higher the speed, the greater the dynamic greater fatigue issues.”
Mitigating vibration means measures on
both the infrastructure and the rolling stock, and ultimately the need to manage vertical elasticity and thus load transmission between the components.
But regular and cyclical maintenance and renewals of the rail, ballast, sleepers
and subsurface has to be taken into account – to prevent costly failures or unscheduled repairs.
Went added that, much as track engineers would prefer hundreds of miles of plain line, maintenance loops and so on, while also considering problems of gradient and vertical acceleration. “That is obviously a problem when you get to the Pennines and Yorkshire and Manchester,” he said.
Substructure
Went said: “The ultimate question is: do you have a ballasted system or do you have a ballastless system? With slab track for example, you have to go through a structured evaluation process and look at the inputs and constraints that your system has to work to; what type of train service are you running – is it mixed, is it high-speed [passenger] network and there’s going to be no freight allowed.
you want be able to go in terms of maintenance, when do you want to renew the system?”
Other key questions, he said, are the track joints on ballasted track, and how slab track might cope with poor ground conditions. One of the most important questions is the transition point between ballasted and slab track.
Went added: “Under-sleeper pads: that in
itself manages the whole interface between the sleeper and the ballast.”
For ballasted track, he said the Los Angeles aggregate abrasion, whereas “Network Rail look at
aggregates in excess of 20”.
The sub-ballast is “critical to the whole track system”, he added, with many civil engineering aspects to consider. “The experience we’ve had with Network Rail is that normally there is a layer of excavated earth that is then compacted, and then you put a ballast on top. That leads to problems, particularly in terms of getting the drainage layers right and making sure you can
“A sub-ballast layer is something we’re seriously considering, because it gives you
Went gave a rundown of some of the leading types of slab track around the world, and the systems have a problem with noise, as noise is surface, so how do you mange that?” The answers tend to be large barriers, or absorbent mats – which both raise further issues and maintenance questions.
Geodynamics
Went told the conference: “The geodynamic element must be understood for the length of any high-speed line. Recognising, in the UK, that we do go through challenging geophysical and geological conditions, we need early examination of this and modelling to understand exactly how the track system will perform. It is fundamentally critical to then deciding on your track system and how that system is built up. Undertaking modelling solutions.”
FOR MORE INFORMATION
W:
www.birmingham.ac.uk/research/activity/ railway/events/high-speed-rail-conference. aspx
rail technology magazine Dec/Jan 15 | 27
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