Tunnel resizing. Is it possible?

[Giugiaro]

I'd like to ask if it's possible to resize a single track tunnel onto a double track, and if this solution is more or less costly than building a second single tunnel parallel to the existing one.

I understand that resizing an already existing tunnel is both dangerous and disrupts railway traffic during the intervention.

Are there any examples of such a procedure being taken or done in the past?

 

[Midnight Sun]

This link may help on rebore of Farnsworth Down Line tunnel

https://www.railengineer.co.uk/2016/03/03/farnworth-tunnel-once-in-a-lifetime/

 

[TRAX]

The first question is can the stuff above the tunnel hold on a widened tunnel or does it need vertical strengthening to hold the ceiling of the tunnel ie. a new single track tunnel ?

 

[Ianno87]

Yes, was done at Farnworth tunnel (between Bolton and Manchester) in 2015.

Helped that the bore being enlarged had previously carried double tracks, but was outgrown by train sizes, so a second bore was added alongside with the original bore becoming to single track.

The second bore then acted as a way of maintaining train services whilst the original bore was enlarged for electrified double track in 2015.

 

[InOban]

Surely a lot would depend on the nature of the material being bored. Up here we have proper rock.

 

[Ianno87]

Farnworth did have a partial collapse of the works during construction due to the poor ground conditions.

 

[Bald Rick]

Yes it’s often possible, but rarely easy. In ‘busy’ parts of the terra firma (eg in cities) tunnels are threaded between all sorts of other things underground - other tunnels, foundations, deep basements, etc. Therefore widening them means eating into these other things, which can get very expensive very quickly.

Running train services through the tunnel whilst doing it is not practical, as the City & South London Railway discovered the hard way in 1923.

 

[pdeaves]

It also depends a lot on what is the other side of the original tunnel walls. Building foundations? Water courses? Military installations?

 

[trivran]

Yes it’s often possible, but rarely easy. In ‘busy’ parts of the terra firma (eg in cities) tunnels are threaded between all sorts of other things underground - other tunnels, foundations, deep basements, etc. Therefore widening them means eating into these other things, which can get very expensive very quickly.

Running train services through the tunnel whilst doing it is not practical, as the City & South London Railway discovered the hard way in 1923.

That would be to say that any notions of enlarging say, 100 year old tube-sized tunnels are at the very least, impractical?

 

[ian1944]

The Penmanshiel collapse in 1979 came as the tunnel height was being increased by lowering the trackbed, and despite the walls not being touched for widening about 20 metres of arch came down. Widening something of comparable age would be unlikely. Removing one wall would mean that that side of the arch would need supporting, so why not leave the wall there and build a new bore adjacent?

 

[transmanche]

That would be to say that any notions of enlarging say, 100 year old tube-sized tunnels are at the very least, impractical?

Indeed, although it has been done. The City & South London Railway (C&SLR) enlarged their running tunnels between Euston and Clapham Common (via Bank) between 1922 and 1924. This was to make their tunnels (a mix of 3.1m and 3.2m diameter) the same size as the other deep-level tube lines (3.6m diameter) so that standard tube stock could be used and through trains operate between the C&SLR and the Charing Cross, Euston & Hampstead railway - later to become the Northern line.

Initially, work on the section south of Moorgate was undertaken at night, with trains running as normal during the day!

 

[Bald Rick]

Indeed, although it has been done. The City & South London Railway (C&SLR) enlarged their running tunnels between Euston and Clapham Common (via Bank) between 1922 and 1924. This was to make their tunnels (a mix of 3.1m and 3.2m diameter) the same size as the other deep-level tube lines (3.6m diameter) so that standard tube stock could be used and through trains operate between the C&SLR and the Charing Cross, Euston & Hampstead railway - later to become the Northern line.

Initially, work on the section south of Moorgate was undertaken at night, with trains running as normal during the day!

Initially, until there was a collapse and a train ran into it. Hence my comment earlier.

It is definitely still practical to enlarge 100 year old tube tunnels - TfL have done it twice in the last couple of years building the junctions for the Battersea branch and the new Bank platform. However it is rather diffficult!

 

[bramling]

Initially, until there was a collapse and a train ran into it. Hence my comment earlier.

It is definitely still practical to enlarge 100 year old tube tunnels - TfL have done it twice in the last couple of years building the junctions for the Battersea branch and the new Bank platform. However it is rather diffficult!

Not universally practical. Done at Kennington, Angel and Euston with little disruption, but not feasible at London Bridge due to the proximity to the river. When the southbound tunnel at London Bridge was diverted in the 1990s the original tunnel was backfilled and the new tunnel bored through the backfill, with a lengthy closure whilst the work was done.

 

[edwin_m]

Not universally practical. Done at Kennington, Angel and Euston with little disruption, but not feasible at London Bridge due to the proximity to the river. When the southbound tunnel at London Bridge was diverted in the 1990s the original tunnel was backfilled and the new tunnel bored through the backfill, with a lengthy closure whilst the work was done.

There is a similar operation going on at Bank, but I'm not sure what technique they are using. There will be a line closure of several months.

 

[Bald Rick]

Not universally practical. Done at Kennington, Angel and Euston with little disruption, but not feasible at London Bridge due to the proximity to the river. When the southbound tunnel at London Bridge was diverted in the 1990s the original tunnel was backfilled and the new tunnel bored through the backfill, with a lengthy closure whilst the work was done.

Agreed, not practical everywhere.

 

[hwl]

There is a similar operation going on at Bank, but I'm not sure what technique they are using. There will be a line closure of several months.

Completely new tunnel ~20m to the west so only the joins at either end to the existing to do during the closure.
The new tunnels are sprayed concrete lining

 

[edwin_m]

Completely new tunnel ~20m to the west so only the joins at either end to the existing to do during the closure.
The new tunnels are sprayed concrete lining

Thanks - do you know how they are joining to the existing? Step plate as per Kennington, fill and re-bore as someone mentioned above was done at London Bridge, or something else entirely?

 

[hwl]

Thanks - do you know how they are joining to the existing? Step plate as per Kennington, fill and re-bore as someone mentioned above was done at London Bridge, or something else entirely?

Fill with foamcrete and cut/dig out with remote control equipment.
The limitation is at the Northern end due to:
DLR below,
Bank of England Vaults to the east,
the ex HSBC (Goldfinger Fort Knox interior) vaults to the west
the northbound Northern line above.

Hence once you are doing that at one end it is far easier and cheap to do that at the south end as well.

And this above ground as well (pretty much all listed):
https://www.google.com/maps/@51.5132892,-0.0888512,3a,75y,337.36h,89.83t/data=!3m7!1e1!3m5!1sjVauA7Le0Ak0MvkrI6ksjw!2e0!6s//geo0.ggpht.com/cbk?panoid=jVauA7Le0Ak0MvkrI6ksjw&output=thumbnail&cb_client=maps_sv.tactile.gps&thumb=2&w=203&h=100&yaw=352.2578&pitch=0&thumbfov=100!7i16384!8i8192

The new tunnel runs under the white coach to the left under the corner of Natwest (not much underneath unlike the old HSBC/Midland vaults in the next building) behind to join the existing just behind the red bus (171) straight ahead on Princes Street.

About as bad as it gets...

Very appropriate for Threadneedle street!

 

[edwin_m]

Fill with foamcrete and cut/dig out with remote control equipment.
The limitation is at the Northern end due to:
DLR below,
Bank of England Vaults to the east,
the ex HSBC (Goldfinger Fort Knox interior) vaults to the west
the northbound Northern line above.

Hence once you are doing that at one end it is far easier and cheap to do that at the south end as well.

And this above ground as well (pretty much all listed):
https://www.google.com/maps/@51.5132892,-0.0888512,3a,75y,337.36h,89.83t/data=!3m7!1e1!3m5!1sjVauA7Le0Ak0MvkrI6ksjw!2e0!6s//geo0.ggpht.com/cbk?panoid=jVauA7Le0Ak0MvkrI6ksjw&output=thumbnail&cb_client=maps_sv.tactile.gps&thumb=2&w=203&h=100&yaw=352.2578&pitch=0&thumbfov=100!7i16384!8i8192

The new tunnel runs under the white coach to the left under the corner of Natwest (not much underneath unlike the old HSBC/Midland vaults in the next building) behind to join the existing just behind the red bus (171) straight ahead on Princes Street.

About as bad as it gets...

Very appropriate for Threadneedle street!

Thanks for that. Let's hope nobody "accidentally" steers the drill too far to the left and stumbles into one of the vaults...

 

[hwl]

Thanks for that. Let's hope nobody "accidentally" steers the drill too far to the left and stumbles into one of the vaults...

All the cutting will be from the ex Midland vaults side which now have restaurant, bar and swimming pool in the vaults (Hotel).

 

[SussexMan]

The Higham and Strood Canal Tunnels were arguably resized in order to lay a double railway track back in the late 1840s. Initially one long canal tunnel, it was split into two to allow a place for canal barges to pass in the middle. Then a single rail track was laid along the canal path inside the tunnel so barges and trains could both use it. The single line was partly supported by the tow path and partly upon wooden piles driven into the canal bed. Later, the the canal was drained and the canal bed in-filled. The tunnel walls were trimmed back to ensure a double-track line could be accommodated comfortably, and the opportunity was taken to install more brick lining.

More info here: https://www.kentrail.org.uk/higham_tunnel.htm

 

[D365]

Completely new tunnel ~20m to the west so only the joins at either end to the existing to do during the closure.
The new tunnels are sprayed concrete lining

Yep, I was going to point that out. The existing southbound tunnel is to be reused as a connecting tunnel for passengers between the existing northbound platform (to be retained) and the new southbound, if I recall correctly.

 

[swt_passenger]

Yep, I was going to point that out. The existing southbound tunnel is to be reused as a connecting tunnel for passengers between the existing northbound platform (to be retained) and the new southbound, if I recall correctly.

Good summary picture here from ianvisits:
https://cdn.ianvisits.co.uk/blog/wp-content/uploads/2018/10/07144343/bank-upgrade-project-08.jpg

 

[VestibuleRider]

Thanks for that. Let's hope nobody "accidentally" steers the drill too far to the left and stumbles into one of the vaults...

This happened in Die Hard With a Vengeance. Great film! Although I think that was the New York Subway, and a bit fanciful!

 

[edwin_m]

Yep, I was going to point that out. The existing southbound tunnel is to be reused as a connecting tunnel for passengers between the existing northbound platform (to be retained) and the new southbound, if I recall correctly.

Basically what happened at London Bridge a few years ago. If you go into the central tunnel there the passages to one platform are much smaller than to the other and arched, because they used to be the connecting passages between the two platform tunnels.

 

[themiller]

If I remember correctly, on the south ramp of the Loetshberg line in Switzerland, at least one tunnel was opened up for 'rolling road' traffic by excavating outside the existing tunnel lining then removing the original lining. The rock in the area makes tunnels self-supporting without a lining - at least in the short term.

 

[Ashley Hill]

Didn't the tunnel at Southampton get enlarged a few years ago?
The tunnels between Dawlish and Teignmouth were also doubled.

 

[hwl]

Didn't the tunnel at Southampton get enlarged a few years ago?
The tunnels between Dawlish and Teignmouth were also doubled.

Soton was covered in the other tunnel thread recently.