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Features List 13
From CAD User Mechanical Magazine Vol 13 No 08 - SEPTEMBER 2000
The Channel Tunnel Rail Link, the £5.2 billion project to design and construct the Channel Tunnel Rail Link (CTRL)
CTRL is being designed and project managed by the
Rail Link Engineering (RLE) consortium
comprising Bechtel, Arup, Halcrow and Systra. RLE manages
the contractors who are building the railway on behalf of client
Union Railways. It will be opened in two
sections, the first in 2003 between the Channel Tunnel and Fawkham
Junction, in north Kent where it will connect with the existing
Railtrack network en route to Waterloo International Station.
Subsequently, Section Two will run beneath the Thames and through
east London to St Pancras, scheduled for completion in 2007.
A design team led by Alan Price, the Section One Lead Design and Construction Engineer, used Intergraph's Civil suite to create the alignments for the route between Fawkham Junction and the Channel Tunnel, a distance of 78 kilometres (46 miles). He said: "We undertook the work using all three Intergraph Civil products: InRail for the track, InRoads for the earthworks and in other areas such as mitigation earthworks and road earthworks we have used SiteWorks.
"All the products are sub-sets of each other with InRail having all the functionality at the top end. Once the alignment for the CTRL is fixed by the trackwork team it is cascaded down to the civil, structural and environmental engineers. "They are using our geometry strings to generate all their earthworks and construction plans," added Mr Price who is also responsible for the Railtrack interface works. The interface is complicated because the CTRL weaves in and out of Railtrack assets. During construction of Section One, existing signalling, track and power supplies have to be modified while keeping the existing service running.
Managing change control
One of their challenges is to manage change control. Mr Price said: "For example, if someone designs a culvert and asks for the alignment to be raised slightly to accommodate the new design, we use [the software] to work out what the implications are in the context of high speed alignment geometry rules. "If you lift the high speed alignment in one place, that has implications over several kilometres. It can involve changes to the track bed and amending the design of several bridges, too. In such cases it often makes sense to ask for the culvert design to be changed instead." A change to the alignment has to be signed off by all disciplines before it is incorporated into the master alignment by the trackwork team.
Mr Price, who advised CTRL consortium members Ove Arup on the choice of technology, says they adopted Intergraph software for the CTRL project because it is flexible and works directly on top of the MicroStation CAD package, removing the need to import and translate data. This means, for example, that when architects produce CAD files for station layouts they can be used as a reference to snap to within InRail. An alignment can be offset from a particular structure by points picked in the graphics without having to rely on translations going backwards and forwards.
Although a lot of CTRL alignment involves plain line design, the software's capability is vital at junctions. For example, where the track branches off into Ashford Station a grade separated junction is required: in other words the tracks have to cross over without coming into contact. This will be achieved with elevated track at one end of the station and an underpass at the other end. "Without designing in three dimensions achieving the correct structural clearances everywhere would be a very complex process," said Alan Price "When you have to create new geometry in this context, the functionality of InRail is very powerful. You can just bolt bits together and move bits around until they are right."
The freight problem
Although the main usage of the CTRL will be by high speed international and domestic trains it has also been designed to accommodate freight. This has been a major challenge for the CTRL. Alan Price explains: "No other high speed line anywhere in the world caters for freight in this way. It means that we need to design for high speed passenger traffic running at 300km an hour while the freight is supposed to run at 140km an hour. "The difficulty is that if you cant the track for a high speed use, you are going to get a lot of wear on the low rail when the freight train rides around it with a higher axle load at a much lower speed, thus increasing maintenance."
The challenge is to "ensure that, by having to cant for the high speed trains, you have not exceeded the criteria for the slower speed ones". InRail allows you to do this. Mr Price explained: "You can create a series of cant profiles for a single horizontal alignment and say "This is what we want to apply if we run at 300 kph and this is the cant we want to apply if we run at 140kph". Then you work out what the optimum is between the two and fix it. "You can generate the cant information and plot profiles for both speeds automatically."
A lot of alignment optimisation was also carried out as a result of close community liaison and trying where possible to address local residents' concerns and environmental criteria on Section One. Mr Price said: "We needed to be in a position to make changes such as lowering an embankment or moving or increasing mitigation earthworks to reduce noise levels. The advantage… was that you could look at all the constraints on screen and move the alignment around until you got what you wanted. "Happily, you can turn alignment changes around very quickly. InRail, InRoads and SiteWorks applications have been invaluable in meeting the tight time-scales required for the infrastructure design on this prestigious project." CU
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