Constructing the Severn Tunnel

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Constructing the Severn Tunnel

Postby philipmartin » Mon May 01, 2017 4:06 am

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Re: Constructing the Severn Tunnel

Postby george matthews » Mon May 01, 2017 4:41 am

This tunnel was much praised and valued when it was built but as with much other 19th century engineering it is very flawed. The constant flow of sea water into it has been dealt with but only at the cost of high energy demands.

This route is being electrified but electrifying this tunnel is a modern problem. I would be interested to know how they are doing that, to avoid the overhead being affected by sea water. The tunnel is located on the main highish speed route between London and Swansea. HST diesel trains are the main users of this route, travelling between London and Swansea. There are also diesel DMUs from Bristol to Cardiff and Swansea. After electrification these would be replaced by electric equivalents. Probably some Cross-Country trains, from Cardiff to Birmingham would continue to be diesel.

The best solution would be to build a modern tunnel, using the knowledge accumulated in the more than a century since this flawed tunnel was built. Another would be to build a barrage to harness tidal power for electricity, and lead a new railway line across it.

Its main purpose was in taking the numerous coal trains from south Wales. As this industry is now defunct a lot of its usefulness has gone, so a new Severn rail crossing is not very likely. There is already a motorway road crossing which takes a lot of the passenger demand for travel.

I have been through it several times. The actual passage through it is as normal as for any other tunnel. For the passenger there is no hint of the difficulties in building and maintaining it.
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Re: Constructing the Severn Tunnel

Postby philipmartin » Mon May 01, 2017 1:32 pm

The Severn Tunnel was a GWR project and Brunel had some influence in it. He himself, when a young man, nearly died constructing the tunnel under the Thames.
https://en.m.wikipedia.org/wiki/Thames_Tunnel
https://en.m.wikipedia.org/wiki/Severn_Tunnel
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Re: Constructing the Severn Tunnel

Postby george matthews » Mon May 01, 2017 2:04 pm

philipmartin wrote:The Severn Tunnel was a GWR project and Brunel had some influence in it. He himself, when a young man, nearly died constructing the tunnel under the Thames.
https://en.m.wikipedia.org/wiki/Thames_Tunnel
https://en.m.wikipedia.org/wiki/Severn_Tunnel

I don't think Brunel had any influence on the design of the tunnel which was built long after his death - and after the gauge of the GWR was changed. Modern practice would have done a thorough geological survey of the route and perhaps would have been able to avoid the water ingress. Probably such a tunnel would have been lower in the ground to avoid the water, and would have been designed to be watertight. It would have resembled the Channel Tunnel in its design. Despite being lower, and therefore subject to greater water pressure, the Channel Tunnel is almost watertight. If a tidal barrage is ever built - something more likely as the need for carbon-free electricity is felt urgently necessary - the tunnel might well be abandoned.
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Re: Constructing the Severn Tunnel

Postby philipmartin » Mon May 01, 2017 10:05 pm

Thanks for the information.
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Re: Constructing the Severn Tunnel

Postby David Benton » Mon May 01, 2017 10:27 pm

Funny with all the chemical technology today, how hard it is to seal a tunnel or other structure. The difficulty i suspect is that it is already a wet environment, I know in my line of work , we have sealants that we could guarantee will work if the surfaces are dry , but as soon as you introduce a bit of water or oil , it is impossible to seal .
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Re: Constructing the Severn Tunnel

Postby george matthews » Mon May 01, 2017 11:50 pm

David Benton wrote:Funny with all the chemical technology today, how hard it is to seal a tunnel or other structure. The difficulty i suspect is that it is already a wet environment, I know in my line of work , we have sealants that we could guarantee will work if the surfaces are dry , but as soon as you introduce a bit of water or oil , it is impossible to seal .

I think after 120 years or so if it was possible to seal the tunnel they would have done it. I think there have been surveys. I think a barrage would be the best solution, justifiable as a generator of electricity on a large scale. But I don't think the government is very favourable to that yet. They are not as hostile to the idea as Trump would be but not yet in favour of finding the money.
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Re: Constructing the Severn Tunnel

Postby johnthefireman » Thu May 11, 2017 2:15 am

george matthews wrote:This route is being electrified but electrifying this tunnel is a modern problem. I would be interested to know how they are doing that


As far as I can recall, at least one of the major tunnels on the route is being electrified with an overhead rail rather than wire for the pantograph to pick up power from. I think that reduces the height, as the rail is solid and doesn't need all the catenary kit which a wire requires.
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Re: Constructing the Severn Tunnel

Postby george matthews » Thu May 11, 2017 8:02 am

johnthefireman wrote:
george matthews wrote:This route is being electrified but electrifying this tunnel is a modern problem. I would be interested to know how they are doing that


As far as I can recall, at least one of the major tunnels on the route is being electrified with an overhead rail rather than wire for the pantograph to pick up power from. I think that reduces the height, as the rail is solid and doesn't need all the catenary kit which a wire requires.

I still wonder whether the use of a rail will be more suitable than a normal catenary. The continual showers of water are a serious risk to the electricity.
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Re: Constructing the Severn Tunnel

Postby johnthefireman » Thu May 11, 2017 8:43 am

george matthews wrote:The continual showers of water are a serious risk to the electricity.


I don't have information on the exact state of the leakage into the tunnel. Is it actually "showers" coming from the roof, or is it leakage down the side walls or seepage around the bottom? Remember that overhead electrification operates outdoors in very heavy rain storms where the masts, conductors and insulators would all be soaking wet for long periods.
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Re: Constructing the Severn Tunnel

Postby george matthews » Thu May 11, 2017 9:33 am

johnthefireman wrote:
george matthews wrote:The continual showers of water are a serious risk to the electricity.


I don't have information on the exact state of the leakage into the tunnel. Is it actually "showers" coming from the roof, or is it leakage down the side walls or seepage around the bottom? Remember that overhead electrification operates outdoors in very heavy rain storms where the masts, conductors and insulators would all be soaking wet for long periods.

The estuary above is salty. Is the water entering the tunnel also salty? As it is conductive that would be a problem for the overhead.
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