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Post by jetblast787 on Aug 8, 2015 13:07:22 GMT
I've worked for LU for nearly the past year in track and while on site visits, I have come across a number of curious standard across the Jubilee, Northern and Picc lines which as been bugging me and my co-workers. I surprisingly haven't taken a clear photo of what I am enquiring about, however the following image is as close as I have to a clear image. If you look closely, you can see the tunnel widens for about 10-15m (note, no access to anywhere else or the other road, just the tunnel rings suddenly widen out) then goes back to 'normal'. Anyone know why the tunnels do this? I suggested that maybe its the point where the tunnels joined up when tunneling from both sides, but it doesn't make sense to have something like this for that reason? i.imgur.com/hU3ypXh.jpgFurthermore, I was between Wood Green and Bounds green and noticed the tunnels come close enough together to cause, well I'll let the image speak for itself. I've never seen anything like this mid way between two stations (I have just after the head/tailwall, but not half way between stations). Is there an engineering reason behind it? Maybe the tunnels being close to one another causes instability (although I don't see this as being a definitive answer)? There is no access or shaft anywhere in the vicinity of where the image was taken, however there were a few cross passages before and after; why they couldn't just build a cross passage I don't know. i.imgur.com/jLR7ga1.jpgAnyone able to shed any light? |
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Chris M
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Post by Chris M on Aug 8, 2015 13:21:43 GMT
My guess regarding the second question is that it relates to the width of the right of way being followed on the surface narrowing so that there is not the required room for the standard spacing between tunnels?
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Post by jetblast787 on Aug 8, 2015 13:26:05 GMT
My guess regarding the second question is that it relates to the width of the right of way being followed on the surface narrowing so that there is not the required room for the standard spacing between tunnels? I'm pretty sure there are other tunnels on the network closer than here with no direct link between the two. And if that was the case why not just increase the ring size to accommodate both roads in this small area? |
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Rich32
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Post by Rich32 on Aug 8, 2015 13:36:14 GMT
I think that the answer to your first question may be to do with relieving air pressure in tunnels. I'm sure someone more knowledgeable will be able to confirm and if I'm correct, provide a better explanation.
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North End
Beneath Newington Causeway
Posts: 1,769
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Post by North End on Aug 8, 2015 21:36:41 GMT
I've worked for LU for nearly the past year in track and while on site visits, I have come across a number of curious standard across the Jubilee, Northern and Picc lines which as been bugging me and my co-workers. I surprisingly haven't taken a clear photo of what I am enquiring about, however the following image is as close as I have to a clear image. If you look closely, you can see the tunnel widens for about 10-15m (note, no access to anywhere else or the other road, just the tunnel rings suddenly widen out) then goes back to 'normal'. Anyone know why the tunnels do this? I suggested that maybe its the point where the tunnels joined up when tunneling from both sides, but it doesn't make sense to have something like this for that reason? i.imgur.com/hU3ypXh.jpgFurthermore, I was between Wood Green and Bounds green and noticed the tunnels come close enough together to cause, well I'll let the image speak for itself. I've never seen anything like this mid way between two stations (I have just after the head/tailwall, but not half way between stations). Is there an engineering reason behind it? Maybe the tunnels being close to one another causes instability (although I don't see this as being a definitive answer)? There is no access or shaft anywhere in the vicinity of where the image was taken, however there were a few cross passages before and after; why they couldn't just build a cross passage I don't know. i.imgur.com/jLR7ga1.jpgAnyone able to shed any light? The most common reason for a short enlargement is where the extra size was required for the erection of a tunneling shield. Quite often such enlargements are associated with a former construction shaft, even if the shaft was backfilled afterwards. If you post the exact locations of the photos I may be able to shed more light, the first appears to be on the Northern Line somewhere between Clapham South and Euston? |
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Post by jetblast787 on Aug 9, 2015 11:27:54 GMT
I've worked for LU for nearly the past year in track and while on site visits, I have come across a number of curious standard across the Jubilee, Northern and Picc lines which as been bugging me and my co-workers. I surprisingly haven't taken a clear photo of what I am enquiring about, however the following image is as close as I have to a clear image. If you look closely, you can see the tunnel widens for about 10-15m (note, no access to anywhere else or the other road, just the tunnel rings suddenly widen out) then goes back to 'normal'. Anyone know why the tunnels do this? I suggested that maybe its the point where the tunnels joined up when tunneling from both sides, but it doesn't make sense to have something like this for that reason? i.imgur.com/hU3ypXh.jpgFurthermore, I was between Wood Green and Bounds green and noticed the tunnels come close enough together to cause, well I'll let the image speak for itself. I've never seen anything like this mid way between two stations (I have just after the head/tailwall, but not half way between stations). Is there an engineering reason behind it? Maybe the tunnels being close to one another causes instability (although I don't see this as being a definitive answer)? There is no access or shaft anywhere in the vicinity of where the image was taken, however there were a few cross passages before and after; why they couldn't just build a cross passage I don't know. i.imgur.com/jLR7ga1.jpgAnyone able to shed any light? The most common reason for a short enlargement is where the extra size was required for the erection of a tunneling shield. Quite often such enlargements are associated with a former construction shaft, even if the shaft was backfilled afterwards. If you post the exact locations of the photos I may be able to shed more light, the first appears to be on the Northern Line somewhere between Clapham South and Euston? What made you guess that location; does the tunnel reveal anything? Its actually somewhere between Moorgate and Angel (I think its between Angel and Old street on the SB). I have however seen dozens of this formation across JNP in random locations. What they all have in common is they don't show any evidence of a backfilled shaft at all, I'll try and look harder next time but 100% sure this is true. Is there somewhere which lists backfilled shafts? (I could use these shafts now with the project I'm working on!) |
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North End
Beneath Newington Causeway
Posts: 1,769
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Post by North End on Aug 9, 2015 16:02:42 GMT
The most common reason for a short enlargement is where the extra size was required for the erection of a tunneling shield. Quite often such enlargements are associated with a former construction shaft, even if the shaft was backfilled afterwards. If you post the exact locations of the photos I may be able to shed more light, the first appears to be on the Northern Line somewhere between Clapham South and Euston? What made you guess that location; does the tunnel reveal anything? Its actually somewhere between Moorgate and Angel (I think its between Angel and Old street on the SB). I have however seen dozens of this formation across JNP in random locations. What they all have in common is they don't show any evidence of a backfilled shaft at all, I'll try and look harder next time but 100% sure this is true. Is there somewhere which lists backfilled shafts? (I could use these shafts now with the project I'm working on!) The reason for knowing it was somewhere on that section is, looking at the section of tunnel beyond the enlargment, one can see the four additional segments in each ring, installed when the tunnel was enlarged in the 1920s. In fact, it's 5 'new' segments, as the key piece is a slightly different profile to the original. This tunnel formation is unique to that section of the Northern. Regarding the location in question, it's noticeable that the section beyond the enlargment has the 'enlarged' profile, but the section in the foreground doesn't. This would suggest this is the transition between a section of enlarged original tunnel, and a section which has been completely rebuilt using all-new segments. I'm not totally sure I recognise the location, but could it be approaching Moorgate crossover, on the southbound? This would add up, as the crossover was installed at the same time the tunnels were rebuilt. There are plans on the intranet showing the location of shafts, but they can be inconsistent. Some are obvious (eg on the Northern around Euston), but others are difficult or impossible to detect even if you know exactly where to look (eg Green Park on Jubilee, or the two temporary shafts at Kennington). |
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pitdiver
No longer gainfully employed
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Post by pitdiver on Aug 9, 2015 20:25:30 GMT
If it's between Bounds Green and Wood Green could it be connected with a ventilation shaft as there's one between the two stations.
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