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Old 15th January 2017, 16:56   #61
Trog
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Originally Posted by HSTEd View Post
Not necessarily, since the station is only a few hundred metres long you could cut and cover the fast lines underneath the station. Its just you can't tunnel the entire approach without it becoming absurdly expensive.
So now we need extra land both sides of the line and both sides of the station, so we can fit in the ramps down into the tunnels under the stations. It would also make maintenance difficult and a dipped tunnel is going to be a drainage liability as it may well need pumping to keep it dry.
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Old 15th January 2017, 17:01   #62
HSTEd
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I'm having difficulty picturing how this allows the loops without excessive land take - any chance of a sketch?
Something like this

The two tracks approach, as we get close to the station then they move apart slightly with pointwork generating the two inner 'loop' lines.
As trains will already have decelerated below 300kph before this work (As demonstrated by the Bombardier OOC study) these inner lines can be put relatively close together.

As we approach the station the fast lines on the outside will drop (using our allowed 2.5%+ gradients) into concrete trenches and go into cut and cover tunnels, allowing the loop lines (where trains will be moving relatively slowly this late in the station approach) to flare out so they are directly over them.
This will provide the space between them for the regulation platform, that can be built to the minimum allowable width because it has a low train passing speed as every train passing is stopping.
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So now we need extra land both sides of the line and both sides of the station, so we can fit in the ramps down into the tunnels under the stations. It would also make maintenance difficult and a dipped tunnel is going to be a drainage liability as it may well need pumping to keep it dry.
Slab track in the station vicinity would reduce the need for regular maintenance access.
And I very much doubt you would need the 9m of total spacing you would otherwise need if you flared the high speed lines around the outside of the stopping lines. [And if the tunnels are more epensive than the extra space then the land take problem clearly isn't critical in the first place]

Additionally the tunnels would be short enough to reduce the problems caused by overpressures in the tunnels that would allow for relatively compact cross sections despite the high speed.

And the cost of a few low power redundant pumps is not going to make any difference to the cost of the project. Pumping arrangements were not an enormous part of the cost of Stratford International After all.

Last edited by HSTEd; 15th January 2017 at 17:02. Reason: Double post prevention system
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Old 15th January 2017, 17:14   #63
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Something like this...
Okay, I'm seeing it now.
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...And if the tunnels are more epensive than the extra space then the land take problem clearly isn't critical in the first place...
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