Tunnel Gauge Widening

[matacaster]

When new large tunnels are proposed, the normal method is to use a Tunnel boring machine (TBM). Many existing railway tunnels were built to a small gauge and now require lots of manual work and time out of use to make them even a bit bigger.

Why not have a rail-movable TBM on rails to ream out existing tunnels to UIC gauge which could be moved from tunnel to tunnel and inched forward by hydraulic rams which use the existing tunnel wall to also stop the circular force knocking the TBM off the track?

It may need a swappable cutting head to cope with difference between chalk and granite for example. The existing tunnel liner (often multiple layers of brick would be cut away together with some of the surrounding rock and then normal concrete liners or concrete spray lining introduced.

A further issue is that an advanced version may be needed to cope with unstable or weak rock formation.

Such a machine might work very well on say Blea Moor Tunnel on S&C.

 

[najaB]

Why not have a rail-movable TBM on rails...

TBMs bore circular tunnels, which doesn't really work if it's rail mounted - it doesn't give the cutting head much to work against:

 

[Diplodicus]

They weigh >1,200 tonnes a piece!

 

[Murph]

If it's a traditional load bearing structural arch masonry tunnel (brick or stone), the existing structural system relies heavily on there being a smooth continuous arch with roughly uniform downward pressure from the overburden. Cutting an arc into the arch is likely to significantly diminish its strength. At a minimum, you'd probably need to do something like extensive high pressure grouting followed by tiebacks/anchors for the existing structure into the surrounding strata before cutting into it. That prep work would stand a good chance of negating the benefits of doing a "simple" TBM job.

If the track level width is already good, digging downward to lower the track bed, underpinning the existing structure is probably much easier, unless you have a tunnel that was so heavily over-engineered in the first place that you can basically get away with removing or significantly weakening the inner layer(s) of masonry. That said, trackbed lowering and underpinning is pretty much exactly the work that was being carried out for OHLE on the ECML's former Penmanshiel tunnel, when it collapsed and closed the ECML for a long time. The Penmanshiel collapse was also enabled by the tunnel going through unstable ground. The major learning lesson from Penmanshiel is don't mess with tunnels through unstable strata, although it may well have been an accident waiting to happen before they started working on it.

 

[Bald Rick]

Why bother buying a TBM and closing a line for a (very) long time to make an existing tunnel bigger, when you could just buy a TBM and build a new line altogether?

 

[quantinghome]

This was done in 1920s on the Northern line. It wasn't...err... entirely successful.

 

[NotATrainspott]

The cost of doing this would be so high that it would be easier just to buy a bog-standard TBM and build a new tunnel alongside. If the original tunnel is two-track, by centring and then lowering the remaining track you could get reasonably large gauges to match what the TBM would provide for the other track.

In all likelihood, either a route will be unimportant enough that it can feasibly be closed for a few months while a construction team works inside to gauge clear properly or it would be too important for any real work to be done on it at all. For example, various suggestions have been made to have the DLR run into the disused Jubilee Line platforms at Charing Cross, which would be feasible because the tunnels are already disused and thus there is no disruption caused by working on them. Conversely, an upgrade of the Central Line would be so difficult that it is a better idea to spend £14.8bn building Crossrail to relieve it instead of trying to do anything big to that line.

 

[snowball]

A real life example will be before us soon with Farnworth tunnel (known on OS maps as Clammerclough tunnel), between Manchester and Bolton. At present there are two bores (of unequal diameters for historical reasons) each housing one track. As far as I know nothing has been officially published about the techniques to be used to get electrification clearance, but it's been stated on here that the larger bore will be enlarged to accommodate both tracks. While this is done there will be single-line working through the other bore, which will then be abandoned.

 

[pdeaves]

Over and above what others have said, if you go cutting away at the top (and possibly sides) of a tunnel (particularly in a busy area like London) you could meet all sorts of things like cables, sewers, building foundations, etc. that you don't want to upset.

 

[WatcherZero]

The downward pressure is why you usually try to go down rather than across or up, either remove ballast and replace it with embedded track or if that's not enough you can try and skim the floor of the tunnel a couple of inches. Mostly your not trying to fit wider trains, just taller because of the OHLE equipment and pantograph.

 

[edwin_m]

This was done in 1920s on the Northern line. It wasn't...err... entirely successful.

Indeed.

http://www.railwaysarchive.co.uk/docsummary.php?docID=2363

The locomotive struck a portion of the timbering which had become dislodged, and some 500 cubic yards (650 tons) of coarse gravel and sand rapidly entered the tunnel, which became completely blocked within about 15 minutes. This caused a crater-like cavity some 45 feet in diameter and 15 feet deep to form below the surface of Newington Causeway ... 40 feet above the top of the tunnel. The cavity extended below the double line of LCC Tramway situated in the centre of the roadway and at the same time robbed electric power and telephone cables, gas and water mains of their support. The result was that escaping gas filled the cavity, and by some means which cannot ascertained, a violent explosion ensued ... about 50 minutes after the failure of the joint in the tube took place. ... a 15 inch water main fortuitously collapsed, thus flooding the cavity and extinguishing the fire. ... I am glad to report that no one was injured.

 

[Ploughman]

On a slightly related topic.

Brotherton Tunnel on the line between Ferrybridge and Burton Salmon.
This was meant to be being considered for total opening out for Container traffic.
Lowering was not an option due to the state of the footings.
(I was in the tunnel on a relay about 7 years back)
Any developments anyone?

 

[NotATrainspott]

On a not-dissimilar note, the two single-bore tunnels under the Forth and Clyde Canal on the Falkirk Grahamston line are to be opened out and the canal put onto a viaduct in order to fit overhead wires. These tunnels are only about a carriage long so it's not going to be incredibly difficult.

 

[RPM]

On a not-dissimilar note, the two single-bore tunnels under the Forth and Clyde Canal on the Falkirk Grahamston line are to be opened out and the canal put onto a viaduct in order to fit overhead wires. These tunnels are only about a carriage long so it's not going to be incredibly difficult.

Do you have a link for that? (Not disbelieving you, just very interested)

 

[NotATrainspott]

Do you have a link for that? (Not disbelieving you, just very interested)

http://www.egip.info/news/2014/10/canal-closes-for-bridge-demolition

 

[RPM]

Interesting. Thanks for link

 

[NotATrainspott]

https://twitter.com/NetworkRailEGIP/status/548915198883815424/photo/1

Before:

After:

 

[RPM]

At the risk of starting up the whole "how do you define a tunnel?" debate, it strikes me that what is being done at Carmuirs is a straightforward aqueduct renewal. The demolished structure was a twin stone arched aqueduct rather than any form of tunnel.