A new Severn tunnel - or other crossing?

[whole diary]

[grahame]

Seeded from ...

Talking to someone who regularly travels to Bridgend from Bristol Parkway they said that in conversation with staff at BPW^» (Bristol Parkway - next trains) the staff are commenting that in the long run it might be cheaper to bore a second Severn Tunnel than to keep spending millions each year TRYING to maintain the present tunnel.

An interesting thought. >

A new Thread perhaps?

Ideas, anyone?   Options??

[ChrisB]

All depends how many years-worth of maintenance adds up to more than the cost of a fresh tunnel.

More than 5 & the short-termism of the Government term will see it kickedinto the next Government (& the next, and the next....)

[broadgage]

I suspect that a bridge might be preferable.
Long tunnels are somewhat risky in case of fire, and this is reflected in the need for elaborate fire precautions in new tunnels.
If fire breaks in a train on a bridge, being in the open air greatly reduces the risks to life. And if all else fails, rescue by air or by sea is possible. Cant do that with a tunnel!
Also a tunnel has an ongoing energy use, for pumping out water, for ventilating, and for lighting. A bridge has negligible ongoing energy use.

Intermediate supports are possible to avoid building a huge and expensive single span. I suspect that most passengers would prefer a bridge.
A walkway for pedestrians and a cycle track would be most useful additions. This should be wide enough to take a fire engine or ambulance in case of emergency, but not be open to road vehicles normally.

The very substantial supports needed for a bridge could also be combined with wind turbine towers.

[johnneyw]

It makes me wonder if repairing and upgrading the old Severn Rail Bridge might have been seen as worthwhile now. Mind you, hindsight is a great thing.

[ellendune]

It makes me wonder if repairing and upgrading the old Severn Rail Bridge might have been seen as worthwhile now. Mind you, hindsight is a great thing.

Except that it was in the wrong place and IIRC^▸ (if I recall/remember/read correctly)  only single track.

[johnneyw]

It makes me wonder if repairing and upgrading the old Severn Rail Bridge might have been seen as worthwhile now. Mind you, hindsight is a great thing.

Except that it was in the wrong place and IIRC^▸ (if I recall/remember/read correctly)  only single track.

Yes, I'm pretty sure it was single track too, hence my mention of "upgrading" the bridge. It's been done before on rail and road bridges but whether the costs would have been prohibitive or not, I can only guess.

[JayMac]

The Severn Rail Bridge would still have been in the wrong place though for services between London and South Wales. Curves would have to be reinstated at Westerleigh (east to north) and Berkeley Heath (south to west). Without those curves its a double reversal, at Westerleigh/Bristol Parkway and Berkeley Road. With the curves Bristol Parkway is bypassed (an important interchange on services between London & South Wales) and the journey time would be increased by around an hour between London and Cardiff.

[Bmblbzzz]

The old Severn Bridge doesn't take much traffic nowadays. Perhaps it could be repurposed with some rails?

(I'm sure it's completely the wrong sort of structure even if it carried on road traffic at all.)

[grahame]

The old Severn Bridge doesn't take much traffic nowadays. Perhaps it could be repurposed with some rails?

(I'm sure it's completely the wrong sort of structure even if it carried on road traffic at all.)

There was thought given to the old Forth Road bridge for light rail and tram:
https://www.transport.gov.scot/media/24880/j10568b.pdf

[stuving]

Surely the only reason for a new tunnel is to do it with a waterproof lining. Can you get TBMs that operate underwater?

[rogerw]

Surely the only reason for a new tunnel is to do it with a waterproof lining. Can you get TBMs that operate underwater?

They had them for the channel tunnel

[johnneyw]

Waterproof relining of the Severn Tunnel? I've got no idea if it's possible, or affordable.

[stuving]

While looking up the history of City Road tube station, I discovered that it closed when the City & South London Line was subjected to a form of angioplasty. It was the original deep tube, and subsequent ones were built with larger-bore tunnels. When it was merged to form (what is now) the Northern Line, its tunnels were rebuilt about 40 cm bigger. Apparently the process was as simple as unbolting the iron lining segments, digging out behind them, and putting them back with small spacers between them.

Presumably much the same could be done to reline modern tunnels, which use precast concrete segments, for whatever reason. It might not work if they are tied or locked together by something hard to remove (such as more concrete). You could use some special-purpose shield structure to make the work easier, especially on large bores.

So on that basis, for a brick-lined tunnel, you would need to cut out some (hopefully not the full depth) of the bricks and insert some lining segments that were capable of being sealed - and resisting the pressure (though that's the case in any tunnel). In the case of the Severn Tunnel, being nothing like round and having that big drain under the floor would make it a wee bit harder, though.

[ellendune]

So on that basis, for a brick-lined tunnel, you would need to cut out some (hopefully not the full depth) of the bricks and insert some lining segments that were capable of being sealed - and resisting the pressure (though that's the case in any tunnel). In the case of the Severn Tunnel, being nothing like round and having that big drain under the floor would make it a wee bit harder, though.

I have worked on tunnels with concrete bolted segmental linings - not much different to their cast iron predecessors. Your would need to put some packers in each joint to sort the angle otherwise some high stresses might build up (the faces are made to quite fine tolerances), but the larger the diameter the less this would be an issue.

I suspect, though, that if you tried that with a brick tunnel lining it was all fall apart and you would just have a heap of bricks! 

[eightf48544]

We had a film on the building of the Severn Tunnel at SWRS^» (Slough and Windsor Railway Society - about) the other week.  It's seems to be rather a miracle that was ever completed once they hit the Great Spring.

Wikipedia has the full story. It took 14 years and Network Rail still pumps 50 million litres a day from the tunnel.

Maybe the Swiss could help they seem able to bore very long tunnels (Gotthard base tunnel 35.5 miles) through all sorts of rock, or as it's under water the Finns and the Estonians with their propose Helsinki to Tallinn tunnel.