London Underground Tunnel Cross Section

[PhilJ W]

By co-incidence I've been archiving some society papers including plans of the GN & City Railway, it has some plans and cross sections of culverts and lift shafts but sadly not tunnels. 

The GN&C can take main line stock, the tunnels are 16' in diameter. Incidently the tunnel ring (or is it rings) were removed for a platform extension.

[rockershovel]

Re circular tunnel rings, the traditional designs are circular for reasons related to the structural strength of the ring itself. Trains don't require circular tunnels to run in, their dynamic envelopes are more-or-less rectangular (hence the pinch points at 11 o'clock and 1 o'clock). The idea of enlarging the tunnel vertically using inserts is difficult to verify using WW1 era design techniques but DID have the great merits of minimum cost, and looking as though it would work.

 

Victorian and Edwardian engineers were BIG on "eyeball engineering", they had a great deal of practical experience and were well aware that they (mostly) worked within broad safety factors, although they couldn't quantify them. If something looked as though it would work, to an experienced eye, they would go ahead and weren't often disappointed.

 

 

This isn't to say that they COULDN'T carry out quite complex stress analysis, but it was not something they would necessarily do

[GoingUnderground]

Indeed there is a tube section at Acton Town. I'm not certain but I think it came from the Central Line.

It's cast iron and sits between the mezzanine level and the storage racking, near to the fragment of the circular escalator, IIRC.

[GoingUnderground]

In looking around for info about the former Stockwell Depot, I came across this site.

 

http://www.gracesguide.co.uk/City_and_South_London_Railway

 

As well as views of the interior of the generating station, it includes an illustration of the original general arrangement of a running tunnel.

 

I also came across this, which refers to the access ramp tunnel.

 

http://vauxhallhistory.org/stockwell-station/

[Nearholmer]

And, if you delve into the appropriate edition of Th Engineer .......

 

The article will fascinate Rocker for the tunnelling detail, as it does me for the electrical content.

 

K

[Dan Hamblin]

I helped certify a modified Rail Wagon (RW814 to be precise) that had been kitted out with plant modules for tunnel lining replacement. This was for a 200m section of the Jubilee Line between Baker Street and Bond Street where the concrete segments were failing due to poor design for the tunnel geometry and depth. The plant was designed around replacing all the segments from track level up with cast iron ones. It was developed by the project team and Harmills, who have supplied quite a bit of plant for our depots on the Underground.

 

Apart from the first and last rings plus some awkward areas, most of the work was done in cancelled Engineering Hours. A really good team of miners, civil engineers, project managers and with help from TransPlant meant that there were no overruns during the project and it won numerous awards.

 

Regards,

 

Dan

[Dan Hamblin]

The CAD expert who did a lot of work on the project planning / sequencing front has put some renders online to show how the wagon set up worked:

 

http://www.coroflot.com/PaulBrown/Tunnel-Segment-Replacement-01

 

Regards,

 

Dan

[Yooski]

What a fantastic response. thank you everyone for your input!

[Engineer_London]

Referring back to posts 25 and 26 on the topic of Great Northern and City tunnels, I recall a cab ride in the final weeks of its operation with tube trains in 1974.  I noticed [and stored the fact away in the recesses of memory] that there were sections of tunnel where the lower half was not segments but a solid structure that formed a circular section.

 

Seeing this particular series of messages has prompted me to find out a bit more.  I don't have to hand the book on the line history which I'm sure will give some background [Bruce, J. Graeme (1976). The Big Tube: A short illustrated history of London's Great Northern & City Railway. London: London Transport. ISBN 0-85329-071-7].

 

However, I've found some time in recent days to look at drawings of the line's tunnels.  An LT transverse section drawing confirms the different tunnel form of my memory.  There are conventional iron segments for the upper half, with 8' inner radius  A drawing note says segments 23" wide.  Lower half of the tunnel is a thicker section - drawing does not have a comment on the material and construction.  This lower half section is shown on the drawing at least twice as thick as the segments.  This 'wall' section seems to be arranged to support and underpin the top half section of segments, and so sits underneath them a bit like a foundation, and gives a slightly reduced tunnel diameter at the waist.  The inside curve of the thick 'wall' runs down each lower side to be exactly at the same level of the invert as the cast-iron section.  I'm reading the drawing as suggesting that the lower half-section's segments were either not installed or removed, rather than encased.

 

Another Metropolitan drawing shows where on the line this modified section was used.  Loosely, it covered both roads from Old Street but not reaching quite as far north as Drayton Park, with a few short gaps mostly at ends of inter-station sections, plus one tiny extra section just south of Old Street on the run towards Moorgate.  This particular drawing has a note referring to the affected tunnel parts as " ... brick inverted ...".  My inference is that the rest of the tunnel run on this line was the pure cast iron circular form.

[GoingUnderground]

Referring back to posts 25 and 26 on the topic of Great Northern and City tunnels, I recall a cab ride in the final weeks of its operation with tube trains in 1974. I noticed [and stored the fact away in the recesses of memory] that there were sections of tunnel where the lower half was not segments but a solid structure that formed a circular section.

 

Seeing this particular series of messages has prompted me to find out a bit more. I don't have to hand the book on the line history which I'm sure will give some background [Bruce, J. Graeme (1976). The Big Tube: A short illustrated history of London's Great Northern & City Railway. London: London Transport. ISBN 0-85329-071-7].

 

However, I've found some time in recent days to look at drawings of the line's tunnels. An LT transverse section drawing confirms the different tunnel form of my memory. There are conventional iron segments for the upper half, with 8' inner radius A drawing note says segments 23" wide. Lower half of the tunnel is a thicker section - drawing does not have a comment on the material and construction. This lower half section is shown on the drawing at least twice as thick as the segments. This 'wall' section seems to be arranged to support and underpin the top half section of segments, and so sits underneath them a bit like a foundation, and gives a slightly reduced tunnel diameter at the waist. The inside curve of the thick 'wall' runs down each lower side to be exactly at the same level of the invert as the cast-iron section. I'm reading the drawing as suggesting that the lower half-section's segments were either not installed or removed, rather than encased.

 

Another Metropolitan drawing shows where on the line this modified section was used. Loosely, it covered both roads from Old Street but not reaching quite as far north as Drayton Park, with a few short gaps mostly at ends of inter-station sections, plus one tiny extra section just south of Old Street on the run towards Moorgate. This particular drawing has a note referring to the affected tunnel parts as " ... brick inverted ...". My inference is that the rest of the tunnel run on this line was the pure cast iron circular form.

To quote page 13 from J Graeme Bruce's book on the GN&C, "A modified method of construction was employed to that used on orthodox tube lines. Cast-iron segments were used, but the lower key pieces were made of concrete and after the formations had been established these were removed and replaced by brick. It was claimed that an advantage of this method of construction was that it reduced the noise level and, being cheaper, alleviated the increased cost between 16 feet diameter and that of 12 feet used for previous and subsequent tube tunnel construction.". Edited July 11, 2017 by GoingUnderground