4 ms·

My laymen's understanding (from various documentaries & articles) is that the expensive part of tunnel construction is managing the transitions between differen

by shabble 10y ago

My laymen's understanding (from various documentaries & articles) is that the expensive part of tunnel construction is managing the transitions between different materials. Boring through hard rock might be slow, but hitting pockets of mud, loose rock and other things (especially when unexpected) can seriously mess up the works, and cause massive delays due to machine damage or reassessment and reinforcement/collapse mitigation. AIUI many (most?) big TBMs are heavily bespoke systems specifically built for their planned route, and it's not unusual to just scrap them after the job is done. So, it's not immediately clear that speeding up the 'easy' part will have a huge impact on the overall outcome, if the bulk of the time & uncertainty is in the hard bits. I wonder if there are any currently underused means of sensing some distance ahead get advanced warning of nasty transitions?

nradov 10y ago
Often the TBM is just left behind in a spur tunnel after finishing the main excavation. It would be too expensive to disassemble and remove.
- abduhl 10y ago
  This is not correct. Most TBMs are advanced into a receiving pit or shaft, disassembled, and moved. Leaving tons of steel in the ground is not cost effective unless schedule is your main driver.
  - nradov 10y ago
    Thanks for the correction. I know there have been tunnels where TBMs were left behind but apparently that's less common than retrieval. http://www.nysun.com/new-york/after-work-done-drills-likely-will-be-buried/46894/ http://www.nysun.com/new-york/after-work-done-drills-likely-... http://www.madehow.com/Volume-6/Tunnel.html http://www.madehow.com/Volume-6/Tunnel.html
tshannon 10y ago
If uncertainty is such a big problem, aren't there any technology solutions for it? Can radar be used to tell the density of materials along the whole boring route?
- taberiand 10y ago
  What about Sonar?
- shabble 10y ago
  I think radar is mostly impractical due to poor signal penetration into the sorts of material (and at the sorts of ranges) that would be useful. Sonar or other acoustic-type seismic sensing (drill holes, place microphone/transducer array, fire small explosive shot, and analyse shockwave propagation) is more practical, but still slow (needs a lot of boreholes), not amazingly high resolution, and probably disruptive to the neighbours if you're in an urban environment. Thinking aloud here (and for all I know, it already happens), something like using oilwell-drilling tech to push a narrow horizontal bore along the tunnel path, and then sending a semi-autonomous sensor robot to do these sorts of scans at regular intervals might be better than drilling the inspection bores from the surface. There's still a bunch of issues if you drill into a pressurised water or mud pocket, but hopefully less than if your 10m-dia main cutter hits same.
sunstone 10y ago
It's likely that Musk has a new technique in mind for tunnelling otherwise what's the point of going it alone? What is the new technique? Well that would be laser drilling into the face on a slight downward slant; then fill that with liquid nitrogen. Wait for a half hour or so for things to freeze up and then smack the whole thing with a huge hammer and it'll all crack right open. Am I dreaming? :)
erikpukinskis 10y ago
> big TBMs are heavily bespoke systems specifically built for their planned route, and it's not unusual to just scrap them after the job is done. Would you say, they are expensive powerful machines built for a single use to be thrown away? Where much of the expense is due to the lack of re-usability? I wonder if Elon Musk has any experience with anything like that.
- loceng 10y ago
  There's no space in Elon's exciting master plans for this boring company..
  - didgeoridoo 10y ago
    Puns aside, it's fun to speculate how this fits in to SpaceX (will need lots of deep tunnels on Mars for habitation and protection from radiation) and Tesla (ventilating tunnels is much easier if the only cars using it are exhaustless). Or, he's just completely mad.
    - loceng 10y ago
      Agreed. It's probably all of the above ... He's reached a point where he has the resources and buy-in and where he understands that the time/cost to accomplish something huge that will support a holistic ecosystem is far outweighed by the value it brings to reduction in cost once at scale. He's not just shooting for the moon or the stars, he's aiming for the edge of the universe.
- shabble 10y ago
  I'm sure there are various ways the work spaceX has done on reuse could apply, perhaps in reliability engineering the most. I recall a statement along the lines of 'we could reuse it, but if X, Y, or Z seriously fails in-situ, we'd spend at least as much as a new machine in trying to extricate and repair it. So we don't.' No doubt bits of the machines are modular and can be salvaged and reused, but especially in urban tunneling, the initial bore access can be very tight, and machines are often assembled in-situ and could never be removed in one piece. That, and the sheer punishment they receive during operation makes an easy-to-dismantle design either more expensive or less performant. Finally, my understanding is that the bulk of the cost (especially in overruns) has little to do with the TBM itself, but rather the delays incurred when the territory doesn't match the map. So the solution would be to make a boring system capable of rapid reconfiguration to handle as many expected and unexpected regions as routinely as possible, rather than going for flat-out speed or ultimate machine reuse.

by shabble 10y ago

nradov 10y ago

Often the TBM is just left behind in a spur tunnel after finishing the main excavation. It would be too expensive to disassemble and remove.

abduhl 10y ago
This is not correct. Most TBMs are advanced into a receiving pit or shaft, disassembled, and moved. Leaving tons of steel in the ground is not cost effective unless schedule is your main driver.
- nradov 10y ago
  Thanks for the correction. I know there have been tunnels where TBMs were left behind but apparently that's less common than retrieval. http://www.nysun.com/new-york/after-work-done-drills-likely-will-be-buried/46894/ http://www.nysun.com/new-york/after-work-done-drills-likely-... http://www.madehow.com/Volume-6/Tunnel.html http://www.madehow.com/Volume-6/Tunnel.html

tshannon 10y ago

If uncertainty is such a big problem, aren't there any technology solutions for it? Can radar be used to tell the density of materials along the whole boring route?

taberiand 10y ago
What about Sonar?
shabble 10y ago
I think radar is mostly impractical due to poor signal penetration into the sorts of material (and at the sorts of ranges) that would be useful. Sonar or other acoustic-type seismic sensing (drill holes, place microphone/transducer array, fire small explosive shot, and analyse shockwave propagation) is more practical, but still slow (needs a lot of boreholes), not amazingly high resolution, and probably disruptive to the neighbours if you're in an urban environment. Thinking aloud here (and for all I know, it already happens), something like using oilwell-drilling tech to push a narrow horizontal bore along the tunnel path, and then sending a semi-autonomous sensor robot to do these sorts of scans at regular intervals might be better than drilling the inspection bores from the surface. There's still a bunch of issues if you drill into a pressurised water or mud pocket, but hopefully less than if your 10m-dia main cutter hits same.

sunstone 10y ago

It's likely that Musk has a new technique in mind for tunnelling otherwise what's the point of going it alone? What is the new technique? Well that would be laser drilling into the face on a slight downward slant; then fill that with liquid nitrogen. Wait for a half hour or so for things to freeze up and then smack the whole thing with a huge hammer and it'll all crack right open. Am I dreaming? :)

erikpukinskis 10y ago

> big TBMs are heavily bespoke systems specifically built for their planned route, and it's not unusual to just scrap them after the job is done. Would you say, they are expensive powerful machines built for a single use to be thrown away? Where much of the expense is due to the lack of re-usability? I wonder if Elon Musk has any experience with anything like that.

loceng 10y ago
There's no space in Elon's exciting master plans for this boring company..
- didgeoridoo 10y ago
  Puns aside, it's fun to speculate how this fits in to SpaceX (will need lots of deep tunnels on Mars for habitation and protection from radiation) and Tesla (ventilating tunnels is much easier if the only cars using it are exhaustless). Or, he's just completely mad.
  - loceng 10y ago
    Agreed. It's probably all of the above ... He's reached a point where he has the resources and buy-in and where he understands that the time/cost to accomplish something huge that will support a holistic ecosystem is far outweighed by the value it brings to reduction in cost once at scale. He's not just shooting for the moon or the stars, he's aiming for the edge of the universe.
shabble 10y ago
I'm sure there are various ways the work spaceX has done on reuse could apply, perhaps in reliability engineering the most. I recall a statement along the lines of 'we could reuse it, but if X, Y, or Z seriously fails in-situ, we'd spend at least as much as a new machine in trying to extricate and repair it. So we don't.' No doubt bits of the machines are modular and can be salvaged and reused, but especially in urban tunneling, the initial bore access can be very tight, and machines are often assembled in-situ and could never be removed in one piece. That, and the sheer punishment they receive during operation makes an easy-to-dismantle design either more expensive or less performant. Finally, my understanding is that the bulk of the cost (especially in overruns) has little to do with the TBM itself, but rather the delays incurred when the territory doesn't match the map. So the solution would be to make a boring system capable of rapid reconfiguration to handle as many expected and unexpected regions as routinely as possible, rather than going for flat-out speed or ultimate machine reuse.