Crossrail tunneling

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eMeS

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About half way down this interesting article, there's a box with the following it it:

Precision of tunnelling route 1mm

Programmed steering and monitoring by GPS
How does GPS work underground?
From memory, the Channel Tunnel TBM's were guided by laser, which I find easier to understand.

Or is the (differential?) GPS just used at the entrance points so as to provide an accurate reference and point the TBM in the right starting direction?
 

LE Greys

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About half way down this interesting article, there's a box with the following it it:



How does GPS work underground?
From memory, the Channel Tunnel TBM's were guided by laser, which I find easier to understand.

Or is the (differential?) GPS just used at the entrance points so as to provide an accurate reference and point the TBM in the right starting direction?
Presumably the latter, unless you have a very sensitive receiver and use some form of low-frequency system.

The TBM is currently lying beside the line just beyond Royal Oak, presumably waiting to be launched. Of course, I was out of film.:(
 

LexyBoy

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Presumably the latter, unless you have a very sensitive receiver and use some form of low-frequency system.

The TBM is currently lying beside the line just beyond Royal Oak, presumably waiting to be launched. Of course, I was out of film.:(
I think one of them has already been moved into position? Only one of the two is now visible from the train.

I don't think GPS could be picked up under, traditional laser alignment in conjunction with GPS at portals & stations seems more likely.
 

Waddon

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One of them has been moved into position, they had to hoist up the footbridge to let it through, don't know if the digging has started yet
 

NY Yankee

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The Crossrail is a new line intended to alleviate the overcrowding on the Tube, correct?

Is it a distinct system or is it another Tube line? I checked out the website and it wasn't clear.
 

futureA

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The Crossrail is a new line intended to alleviate the overcrowding on the Tube, correct?

Is it a distinct system or is it another Tube line? I checked out the website and it wasn't clear.
It is a distinct system which will use mainline size rolling stock.
 

brianthegiant

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The Crossrail is a new line intended to alleviate the overcrowding on the Tube, correct?

Is it a distinct system or is it another Tube line? I checked out the website and it wasn't clear.
the closests comparable system is the Paris RER (which shares ticketing with their metro but uses completely different infrastructure) except that the RER uses double deck carriages. Our new crossrail tunnels are being built large enough for double deck trains. but there are sections of older lines used which are not yet compatible with double deck trains.
 

JGR

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the closests comparable system is the Paris RER (which shares ticketing with their metro but uses completely different infrastructure) except that the RER uses double deck carriages. Our new crossrail tunnels are being built large enough for double deck trains. but there are sections of older lines used which are not yet compatible with double deck trains.
Within Île-de-France, all rail tickets are unified, as near as matters.
In terms of scale and form, crossrail 1 is comparable to RER line A (one branch of which goes within a few stone throws of my old house).

If I remember correctly the crossrail OHLE is not being put high enough to fit a double-decker anyway, but could be raised in theory. The lines outside Paddington are not suitable for double-deckers at any rate.
 

RichmondCommu

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Within Île-de-France, all rail tickets are unified, as near as matters.
In terms of scale and form, crossrail 1 is comparable to RER line A (one branch of which goes within a few stone throws of my old house).

If I remember correctly the crossrail OHLE is not being put high enough to fit a double-decker anyway, but could be raised in theory. The lines outside Paddington are not suitable for double-deckers at any rate.
As far as I know its the Connaught Tunnel which prevents double deck trains from being used. I'm pretty sure that the Heathrow tunnels are big enough to accomodate double deck trains.
 

LE Greys

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As far as I know its the Connaught Tunnel which prevents double deck trains from being used. I'm pretty sure that the Heathrow tunnels are big enough to accomodate double deck trains.
There are simply too many bridges, including the car park "tunnels" at Ealing Broadway, that would have to be raised to accommodate double-deckers. It might be possible to squeeze DD stock into W10 loading gauge, and there's certainly the width to do it, but it's mostly a question of height and OHLE positioning. Also, any DD stock trying to go beyond Airport Junction would immediately run into Stockley Road Bridge, which has not seen much change since 1890 when the line was quadrupled.
 

Waddon

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I can't see any demand for double decker trains west of London for non-intercity services in the foreseeable future, as 2 and 3 car dmus are the order of the day currently, and are to be replaced by 10 (potentially 12) carriage crossrail trains with a huge increase in capacity... I'm assuming the tunnels have just been made sensibly future proof, I doubt it's something that's going to be needed in the next 40 years.

Although (in my fevered imagination) it wouldn't surprise me if some enterprising freight company asks about using the tunnels off peak or night time for an east-west freight link some time in the future...
 

JGR

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Although (in my fevered imagination) it wouldn't surprise me if some enterprising freight company asks about using the tunnels off peak or night time for an east-west freight link some time in the future...
There's the North London Line for that sort of thing. I somehow doubt that Crossrail will get any use for freight.
 

brianthegiant

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As far as I know its the Connaught Tunnel which prevents double deck trains from being used. I'm pretty sure that the Heathrow tunnels are big enough to accomodate double deck trains.
Hmm, the Connaught tunnels were originally going to be repaired/re-lined/otherwise patched up. But more recently they've decided that wasn't feasible/economic. But they are now to be completely rebuilt (using a temporary coffer dam to drain the docks above). So if the're being rebuilt completely then I would assume the current wisdom of building in passive provision for DD stock would apply?

Nonetheless there are still lots of other structures along the existing lines used which would also require costly rebuilding, so we wont see DD trains any time soon.
 

Peter Mugridge

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Pity. It would have been quite nice to be able to bash Z20500s through London!

Could anyone Photoshop a Z20500 into Crossrail livery and / or LO livery anyway, just to see what they'd look like?
 

dosxuk

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Hmm, the Connaught tunnels were originally going to be repaired/re-lined/otherwise patched up. But more recently they've decided that wasn't feasible/economic. But they are now to be completely rebuilt (using a temporary coffer dam to drain the docks above). So if the're being rebuilt completely then I would assume the current wisdom of building in passive provision for DD stock would apply?
There's three parts to the Connaught tunnels - the two approaches, which are a twin track brick built cut and cover tunnel, and a central part, which are a pair of single track iron tubes.

Originally, the plan for crossrail was to dredge the dock basin back, and put a concrete cap above the tunnels, and the remove the iron rings, fill it with with a concrete "foam" and then bore out newer larger tunnels. They've since found that the tunnel is a lot closer to the dock bottom than expected, so they're now going to (as you say) dam off the dock and dig it out from above.

Neither of these plans affect the approach tunnels, which are still being repaired and cleaned up as originally planned, and will still affect the loading gauge of the route.

[See also: http://www.ianvisits.co.uk/blog/2012/02/02/photos-inside-a-future-crossrail-tunnel/]
 

Clip

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Seems odd that to open up the tunnels in question you would raise them - why not just lower the trackbed instead or is that deemed far more complicated?
 

jopsuk

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"just" lowering the track bed is rather complicated- tunnel structures (especially tubular ones, but other shapes as well) use the base of the tunnel as part of the load bearing structure (especially through land such as the loam in the docklands) and there's probably very little between the current trackbed and the base of the tunnel.
 

DownSouth

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About half way down this interesting article, there's a box with the following it it:
Precision of tunnelling route 1mm

Programmed steering and monitoring by GPS
How does GPS work underground?
From memory, the Channel Tunnel TBM's were guided by laser, which I find easier to understand.

Or is the (differential?) GPS just used at the entrance points so as to provide an accurate reference and point the TBM in the right starting direction?
For what it's worth, the two ends of the Alice Springs to Darwin line were built independently from each end and they met with a mere 4 mm offset. Not bad considering the length of the line is 1,420 km, well over double the length of the WCML from London to Glasgow. But there are no tunnels so it's an easy job!
 

LE Greys

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For what it's worth, the two ends of the Alice Springs to Darwin line were built independently from each end and they met with a mere 4 mm offset. Not bad considering the length of the line is 1,420 km, well over double the length of the WCML from London to Glasgow. But there are no tunnels so it's an easy job!
And underground, the Ancient Greeks managed quite well in Samos in the 5th Century B.C. using optical instruments without lenses. More recent canal tunnels in the 18th Century had the benefits of compasses and lenses, and usually managed to get within an inch of alignment, noteably Standedge Tunnel, which at its deepest point is 638ft beneath the surface. One railway example where they got it wrong is Kinghorn Tunnel, which has a kink in it because the two contractors disagreed as to the alignment.
 

swt_passenger

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...only to the west!!!

What about the eastern end??? GA???
Shenfield will be in the PAYG area shortly anyway as per the new franchise spec, presumably with special fare zones in the way Watford Jn and the c2c extensions were done, and of course Abbey Wood is already in the zones.
 

Peter Mugridge

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These are Z20500s: http://yvaugeois.free.fr/html/automotrices/Z20500.htm

My favourite double deckers, both in terms of external visual design and internal design for riding on.



I think by 1970s style you might be thinking of the MS61 units: http://www.google.co.uk/search?tbm=...3l4718l0l6140l4l4l0l0l0l0l47l188l4l4l0.frgbld. which have extroadinarily musical motors, especially when you hear them echoing off the long tunnel between Etoile and La Defense... :D


The illuminated stations route maps ( with the next stop flashing ) are a fairly recent innovation and are being increasing fitted to new builds as well as to refurbished older stock; they are an excellent idea.
 
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DownSouth

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Sydney-style DD units could be worth considering. The distinctive thing compared to DD units from Europe or the USA is that Australian railways use high-level platforms like Britain. The amount of infrastructure changes needed might not be that huge, the new H set is only 620mm (About 2 ft) taller than an Electrostar.
 
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