13 ms·

The Evolution of Tunnel Boring Machines (2023)

93 points by chautumn 2y ago

dkga 2y ago
Nice text! I’m just surprised at the lack of mention of the techniques used in the Gotthard in the 19th century.
bluGill 2y ago
Despite TBMs being used all the time it is genererally much cheaper to build a tunnel by cut and cover - that is just call in excovators and dig a hole then cover it. when an excavator breaks you push it aside and get another until it is fixed. Want to go faster - just hire more excavators the overall cost is the same since you are done faster. tbms are cheaper if you must go deep, but deep is a negative for subways since people must get down which takes time (faster is always better). It is claimed that cut and cover is toa much surface disruption - but cut and cover is much faster and so the disruption to any one place can be quick enough. Better to manage disruption than eliminate it. when a tbm breaks your project is delayed while you wait for parts and then fix it in place. Tbms do go under everything else, but experience proves you can find things and go around them quick enough (sometimes there is a delay as somethingeof archeological interest is found - but evperience shows this is still cheaper than a TBM. Yes TBMs are cool and useful but the simple shoud not be over looked
- rsynnott 2y ago
  Thing is, you’re often building these under already-existing things. The Dublin metro project is facing significant planning challenges on the basis that thousands of homes and businesses passed can complain about speculative vibrations from the TBM; with cut and cover it would just be a complete nonstarter (I think one small section is planned to be cut and cover, but most of it will be either bored or surface rail).
  - bluGill 2y ago
    That is a poor excuse - places with much worse problems have don cut and cover.
- aaron695 2y ago
  > it is genererally much cheaper to build a tunnel by cut and cover Coolo, you are building tunnels in a city that doesn't exist yet. Start here - https://en.wikipedia.org/wiki/Opportunity_cost https://en.wikipedia.org/wiki/Opportunity_cost Do you have any interesting examples of modern day cut and cover that are not part of a TBM run? > TBMs are cool and useful They are what is needed to move humanity forward. You have trillion $ centers that using 3D you can add massive amounts of access to. This is not like reclaiming land from water, which is ~stealing, this is value adding through topography, it's creation.
  - lukan 2y ago
    I vouched for this comment, but you might want to check your general style of communication and then email dang about your apparent shadow ban.
  - bluGill 2y ago
    The tunnel will be around for 100 years. Not much ophortunity cost is lost. And you lose the ophortunity cost of what ever you would spend the saved money on for ever. A longer line for example.
- tobylane 2y ago
  You're often not just building under existing things, but through them. We now have a lot under the roads. The Victorians built the subsurface lines of the London Underground with cut and cover, but Oxford is currently suffering overrunning works to lower a road under the station, because of unknown brick arches and utilities. Even the TBMs are building beside existing tunnels and basements. What projects in developed countries have used cut and cover recently? In trying to find out, I see that HS2 under west London and the Canada line under Vancouver chose tunnels over cut and cover because it was cheaper.
  - lytfyre 2y ago
    > I see that [...] Canada line under Vancouver chose tunnels over cut and cover because it was cheaper. Canada Line was mostly Cut-and-Cover - only the bits below downtown and crossing below the water were bored, the bulk of the underground was done cut and cover for cost and speed to make sure it opened for the 2010 olympics. It was not a popular choice - not really announced before the project was approved, and local businesses along the route took a big hit. Vancouver's current Broadway Line Extension is being done with TBMs to avoid the impact that the cut and cover canada line segment construction had.
    - mitthrowaway2 2y ago
      It also resulted in a rail line that has to slow down significantly to round screeching curves along the path of the road above.
  - peterpost2 2y ago
    > What projects in developed countries have used cut and cover recently? I know in Sweden the Västlänken project partially used cut-and-cover at least for the part going southwards.. https://en.wikipedia.org/wiki/West_Link https://en.wikipedia.org/wiki/West_Link
  - bluGill 2y ago
    The article said out of 89 current projects 80 were TBM so it isn't surprising you don't know of the exceptions. I don't off the top of my head either.
- Haemm0r 2y ago
  More information on cut and cover: https://de.m.wikipedia.org/wiki/Neue_%C3%96sterreichische_Tunnelbaumethode https://de.m.wikipedia.org/wiki/Neue_%C3%96sterreichische_Tu... (better translate from the german version, as it has more information and examples)
  - abduhl 2y ago
    This is not cut and cover. Cut and cover is when you "cut" an excavation from the ground surface down and then "cover" it back up with dirt after constructing the structure you want below ground. You have linked to an article on NATM, which is a conventional (read: non-TBM) tunneling method.
    - bluGill 2y ago
      Cut and cover often is cover than dig - there are a lot of options
      - abduhl 2y ago
        Cut and cover is what I described: excavate down, build the structure, cover it up. I am aware that there are lots of options, you can browse my comment history and see that I probably have more experience designing and constructing underground infrastructure (and tunnels in particular) than anyone else that posts on HN.
        bluGill 2y ago
        Cut and Cover is often used in transit conversations to mean any variation where you dig from the surface and not the construction method that is cut and cover. These are two different domains talking about different things that are related. Something we both need to be more aware of in conversations.
        deleted 2y ago
        [deleted]
- jeltz 2y ago
  Cut and cover only works if your subway follows streets. Yeah, I think we should do that where it makes sense but quite often you need to go under buildings or hills.
  - bluGill 2y ago
    Most of the time your subway will follow streets though. Your city has built around the existing streets and people have set their lives up around the places they can get to by the existing streets. If there are two points that are near each other as a crow flies but difficult to reach (shore to an island where there is no nearby bridge) people have made sure they don't need to go there and so you rarely gain much by giving them some new ability. While if you build on the streets they can now go places they were already going via your new subway. Note that I said street and not highway. Some highways (limit access) are good for longer trips, but your subway would be better off using a side street parallel to the highway since while most people use the highway your subway doesn't need to get to any point on the highway while points on the side street - while of limited interest have at least some interest. City transit design is a complex subject that whole books are written about (sadly the people who are in charge don't read them)
    - Symbiote 2y ago
      That seems a very car-centric or American view, with cities built on a grid. Older cities without existing grids can have older metro lines following streets (a limitation of the time they were built, by cut and cover) but newer ones generally don't follow streets. They provide more direct routes, and new crossings over rivers or to islands. Look at Prague or especially Copenhagen for example. https://openrailwaymap.org//mobile.php?style=standard&lat=55.67858860616847&lon=12.583551406860352&zoom=15 https://openrailwaymap.org//mobile.php?style=standard&lat=55...
      - bluGill 2y ago
        Streets have existed since cities began is prehistory times. even before cars people needed to get around.
- potato3732842 2y ago
  TBMs are for going around problems. Compared to cut and cover you can ignore entire classes of people who would be, expensive, delaying obnoxious stakeholders. <gestures at the contents of an average HN comment section whenever the subject is public infrastructure>
- yongjik 2y ago
  My neighborhood in Seoul got a new subway line while I grew up, I believe they used cut-and-cover (it was almost at the outskirt, so they didn't have anything else underground) and it took several years. So, while it's doable, it's not exactly "Just dig a hole, build the tunnel and cover, done." It's a major disruption to shops along the street.
  - bluGill 2y ago
    It is a major disruption for a couple years.
- larsga 2y ago
  It's not a choice of TBM vs cut-and-cover. You also have drill-and-blast. Which method is better depends on a number of factors, including depth and the state of the soil/rock you're going through. A problem with TBMs is it can be difficult/costly to secure the tunnel sufficiently against water ingress. If you mess up that one the cost of your tunnel can easily double or more. Here in Norway we recently built a railway tunnel with TBMs (Blixtunnelen) and it's having problems with water ingress. A fairly mild problem relative to how bad these can get, but it's enough that the tunnel constantly has to be closed for repairs to the railway infrastructure due to water drips.
  - bluGill 2y ago
    There are many options with different compromises. Cut and Cover comes in many different versions (some of them you build the cover first and then dig under that). However I'm going to double down and suggest that despite the disadvantages everyone else has raised the overall much lower cost of cut and cover, combined with the advantages of a shallower tunnel, makes it the right answer for a lot more situations. Most people claiming to need something else for some local feature are wrong - they can work around that other objection and be better off. Note that I'm not saying the objection is invalid, just that it should be worked around.
    - Symbiote 2y ago
      Are you a tunneling engineer? That over 90% of projects are using TBMs strongly suggests they're usually the better option.
      - bluGill 2y ago
        They are the political option. They disrupt the surface the least and so there are less political objections even though they cost more around the world. Tunneling engineers do what the customer says. They will tell you what the options are and what they cost then let the customer choose the evpensive option if they want. Their job isn't to choose between options it is to eliminate the impossible (unsafe) ones and let the customer choose the pros andecons of the rest.
- pjc50 2y ago
  Cut and cover is basically unusable in cities because you'd have to "cut" down all the buildings you'd otherwise tunnel under. There isn't some industry saying "yes we could cut and cover here, but we prefer the slower more expensive option of a TBM"! (I see NATM mentioned; there have been safety issues https://www.hse.gov.uk/pubns/natm.htm https://www.hse.gov.uk/pubns/natm.htm ) The HS2 cut and cover tunnels were all in greenfield: https://www.hs2.org.uk/building-hs2/tunnels/green-tunnels/ https://www.hs2.org.uk/building-hs2/tunnels/green-tunnels/ ; much of the cost there goes on planning and documentation, an under-appreciated cost. It's also questionable as to whether they were needed at all; a plain cutting with embankment open to the air would have been fine from a civil engineering point of view, or even in many places just flat track, but the tunnels were planned because people objected to a railway running through fields.
  - lytfyre 2y ago
    >There isn't some industry saying "yes we could cut and cover here, but we prefer the slower more expensive option of a TBM"! At least for Vancouver, there was absolutely an industry arguing for the slower-more-expensive TBM option on a route that followed exactly a road (the Broadway line extension) - local businesses along the route. The previous line which was mostly done by Cut-and-Cover (the Canada Line) had a very major impact on businesses along the route for years. There are plenty of people who will acknowledge that something is cheaper _overall_ but the impact on a small group being higher can make them extremely vocal, and that has to be managed in public projects.
rsynnott 2y ago
So it doesn’t seem to be mentioned here, but has there been some major recent change in the economics of the _scale_ of the tunnels? Dublin’s beleaguered metro project recently put out its new design; there are a bunch of changes from the previous early-noughties design, but one of the more eyebrow-raising ones is that the bored sections will now be a single _9.5 meter diameter_ tunnel; it is claimed that this is less disruptive and cheaper than the two-narrow-tunnel approach used in conventional bored metros. Recent metro lines is Barcelona and Madrid have also used the single-giant-tunnel approach. Anyone know what’s going on here? Intuitively you’d expect two small tunnels to be cheaper; you’re moving a lot less material.
- timschmidt 2y ago
  I suspect the cost is not in volume of material removed, but in operation and maintenance of the machine and it's crew. One tunnel instead of two is half as much machine and crew time.
  - freeopinion 2y ago
    Please explain how you reasoned this out. If one 9.5m tunnel requires 70 m³ of removal for every meter of forward progress, and two 5m tunnels requires 40 m³ of removal for every meter of forward progress, won't it take nearly twice as long to dig the single larger tunnel? Won't that require twice the machine hours and twice the crew hours? How does the volume of material removed not directly impact machine and crew costs?
    - jcgrillo 2y ago
      Two dump trucks can't pass eachother in a 5m tunnel. That'll put a restrictive upper bound on material removal rate which isn't present in the larger tunnel.
      - Symbiote 2y ago
        Note they use railway trucks to remove spoil (and transport everything else) from a TBM. A narrow gauge temporary track behind the TBM as it advances.
baumschubser 2y ago
I want to mention a recent extension to Berlin‘s subway system right in the middle of the city, in swampy ground and below a canal. They injected „freeze lances“ into the ground, turned 43,000 m^3 of mud into an ice block and then carved their way through it. Absolutely amazing engineering, I think planned and executed by a Swiss company.
- Haemm0r 2y ago
  Got a link for this? I am interested :-)
  - getwiththeprog 2y ago
    I can find https://www.berlin.de/en/news/8097068-5559700-stabilization-work-u2-tunnel-alex-friday.en.html https://www.berlin.de/en/news/8097068-5559700-stabilization-... Which states that due to sandy soil concrete was injected with lances. It was done by a French company. Might be the same tunnel?
- pwarner 2y ago
  Big Dig also used ground freezing. https://babelniche.com/2024/01/17/innovations-of-the-big-dig-2-slurry-jacking-freezing/ https://babelniche.com/2024/01/17/innovations-of-the-big-dig... And the Erie Canal dig the sections through swampy ground in the winter. That was partially to avoid Malaria. Circa 1825
- padenot 2y ago
  This is also a technique that was used more than 100 years ago for the line 4 of the Paris métro: https://www.ratp.fr/en/discover/out-and-about/culture/history-metro-line-4 https://www.ratp.fr/en/discover/out-and-about/culture/histor...
  - llsf 2y ago
    Funny that they had to freeze the ground to dig it, as it is one of the hottest line in Paris (at least 20 years ago).
ReptileMan 2y ago
How is The Boring Company doing lately? There will be huge induced demand for tunnels if they manage to deliver even close to their goals.
- grecy 2y ago
  Slow and steady progress. They’re just about to go big in Vegas, with tunnels the length of the strip.
  - youngtaff 2y ago
    The strip is 4 miles long… when Musk company can bore longer, wider tunnels avoiding other infrastructure e.g. London tube lines, sewers etc then they might have something to shout about
    - ggm 2y ago
      I believe he is deliberately targeting low process burden, low soil resistance targets. He isn't aggressively chasing contracts for complex, deep, large tunnels working around existing infra, or rail, he's chasing places which want disruptive change in transport. Nobody has explained to me what the boring company has actually done innovating TBM, the machines themselveds distinct from a cash injection and some energy from Musk as lead investor. TBM are flow process. It's a pipeline of inputs and outputs. It's scheduling. The LV tunnel isn't a complete success either. It's not operating completely as promised yet is it?
- DonHopkins 2y ago
  [flagged]
  - h3rsko 2y ago
    Its a special "kind of fraud and failure" that launched 90% of mass to LEO in 2024.
    - 2y ago
deleted 2y ago
[deleted]
ChrisArchitect 2y ago
(2023) Some more discussion then: https://news.ycombinator.com/item?id=37836889 https://news.ycombinator.com/item?id=37836889
kitd 2y ago
Interesting article. This bit was not what I was expecting: Today, rock tunneling machines have achieved tunneling rates of over 700 meters per week, and soil tunneling machines have achieved rates of over 200 meters per week, though this is dependent on the size of the TBM Ie, that rock tunneling can be > 3x quicker than soil tunneling.
- ewhanley 2y ago
  Rock often has sufficient structural integrity to get by with some bolting vs adding structure (steel, shotcrete, etc) to the soil tunnel as they go
  - Gibbon1 2y ago
    It never seems to get stated directly by tunneling through stable rock has to be really easy. Like if you can drill and blast your way through you just need a small crew of workers and a dump truck. There is a half mile long tunnel in the California desert that an addled miner made with hand tools and dynamite over 38 years. Self funded and part time. https://en.wikipedia.org/wiki/Burro_Schmidt_Tunnel https://en.wikipedia.org/wiki/Burro_Schmidt_Tunnel Then digging through unstable rock with water intrusion and danger of flooding the costs have to go way way up.
bilsbie 2y ago
I wonder how far off we are from vaporizing the material and venting it out of the tunnel. Probably way more expensive but you could go faster and don’t need to deal with hauling the material out. It might glassify the surrounding soil and make its own support structure too.
- gosub100 2y ago
  This topic has been mentioned in regards to digging super deep bore holes for geothermal energy. The high temps a couple miles down started to soften metal drill bits but some companies are working on lasers that are capable of melting rock to allow further digging.
  - lightedman 2y ago
    An 80W CO2 LASER is plenty of power. I regularly engrave the living shit out of stone with mine, and that goes a few millimeters deep. Get a couple kW in the same wavelength (10640nm) with a proper adjustable focus (movable diopter) and a galvo and a vacuum assist and you can just start raster-scanning your way through the rock.
bilsbie 2y ago
Has anyone studied how roots tunnel underground so effectively? Maybe we can copy aspects of that.
- staplung 2y ago
  Yes, they have been. The growing tip of a root is called the root apical meristem[1] but the short story is that they work effectively by being tiny and taking years or decades to develop, so not all that helpful in terms of making things easier or cheaper. They also can't really go through rock, though they can often split them, particularly if they have fractures already. [1]: https://en.wikipedia.org/wiki/Meristem#Root_apical_meristem https://en.wikipedia.org/wiki/Meristem#Root_apical_meristem
yongjik 2y ago
While we're talking about cool boring technologies... I once heard that Seoul's Bus Terminal Station, line 9, was a particularly difficult case. Line 9 had to go beneath existing line 3, but it couldn't go too deep because it (obviously) needed to connect to the rest of the line. In the end they thrust a group of horizontal steel pipes to stabilize the soil and dug beneath it - and those pipes were 15 cm(!) below existing line 3.
- abduhl 2y ago
  This ground support method is called spiling, for those interested.
extraduder_ire 2y ago
Has anyone attempted to use water jets with aggregate, like you would on a CNC waterjet cutter, for boring through rock? Had this thought the other day and wondered if there would be any advantages over metal cutting teeth. From the article, I gather that replacing cutting teeth isn't that much of a problem nowadays so that mitigates one advantage it might have.

93 points by chautumn 2y ago

dkga 2y ago

Nice text! I’m just surprised at the lack of mention of the techniques used in the Gotthard in the 19th century.

Despite TBMs being used all the time it is genererally much cheaper to build a tunnel by cut and cover - that is just call in excovators and dig a hole then cover it. when an excavator breaks you push it aside and get another until it is fixed. Want to go faster - just hire more excavators the overall cost is the same since you are done faster. tbms are cheaper if you must go deep, but deep is a negative for subways since people must get down which takes time (faster is always better). It is claimed that cut and cover is toa much surface disruption - but cut and cover is much faster and so the disruption to any one place can be quick enough. Better to manage disruption than eliminate it. when a tbm breaks your project is delayed while you wait for parts and then fix it in place. Tbms do go under everything else, but experience proves you can find things and go around them quick enough (sometimes there is a delay as somethingeof archeological interest is found - but evperience shows this is still cheaper than a TBM. Yes TBMs are cool and useful but the simple shoud not be over looked

rsynnott 2y ago
Thing is, you’re often building these under already-existing things. The Dublin metro project is facing significant planning challenges on the basis that thousands of homes and businesses passed can complain about speculative vibrations from the TBM; with cut and cover it would just be a complete nonstarter (I think one small section is planned to be cut and cover, but most of it will be either bored or surface rail).
- bluGill 2y ago
  That is a poor excuse - places with much worse problems have don cut and cover.
aaron695 2y ago
> it is genererally much cheaper to build a tunnel by cut and cover Coolo, you are building tunnels in a city that doesn't exist yet. Start here - https://en.wikipedia.org/wiki/Opportunity_cost https://en.wikipedia.org/wiki/Opportunity_cost Do you have any interesting examples of modern day cut and cover that are not part of a TBM run? > TBMs are cool and useful They are what is needed to move humanity forward. You have trillion $ centers that using 3D you can add massive amounts of access to. This is not like reclaiming land from water, which is ~stealing, this is value adding through topography, it's creation.
- lukan 2y ago
  I vouched for this comment, but you might want to check your general style of communication and then email dang about your apparent shadow ban.
- bluGill 2y ago
  The tunnel will be around for 100 years. Not much ophortunity cost is lost. And you lose the ophortunity cost of what ever you would spend the saved money on for ever. A longer line for example.
tobylane 2y ago
You're often not just building under existing things, but through them. We now have a lot under the roads. The Victorians built the subsurface lines of the London Underground with cut and cover, but Oxford is currently suffering overrunning works to lower a road under the station, because of unknown brick arches and utilities. Even the TBMs are building beside existing tunnels and basements. What projects in developed countries have used cut and cover recently? In trying to find out, I see that HS2 under west London and the Canada line under Vancouver chose tunnels over cut and cover because it was cheaper.
- lytfyre 2y ago
  > I see that [...] Canada line under Vancouver chose tunnels over cut and cover because it was cheaper. Canada Line was mostly Cut-and-Cover - only the bits below downtown and crossing below the water were bored, the bulk of the underground was done cut and cover for cost and speed to make sure it opened for the 2010 olympics. It was not a popular choice - not really announced before the project was approved, and local businesses along the route took a big hit. Vancouver's current Broadway Line Extension is being done with TBMs to avoid the impact that the cut and cover canada line segment construction had.
  - mitthrowaway2 2y ago
    It also resulted in a rail line that has to slow down significantly to round screeching curves along the path of the road above.
- peterpost2 2y ago
  > What projects in developed countries have used cut and cover recently? I know in Sweden the Västlänken project partially used cut-and-cover at least for the part going southwards.. https://en.wikipedia.org/wiki/West_Link https://en.wikipedia.org/wiki/West_Link
- bluGill 2y ago
  The article said out of 89 current projects 80 were TBM so it isn't surprising you don't know of the exceptions. I don't off the top of my head either.
Haemm0r 2y ago
More information on cut and cover: https://de.m.wikipedia.org/wiki/Neue_%C3%96sterreichische_Tunnelbaumethode https://de.m.wikipedia.org/wiki/Neue_%C3%96sterreichische_Tu... (better translate from the german version, as it has more information and examples)
- abduhl 2y ago
  This is not cut and cover. Cut and cover is when you "cut" an excavation from the ground surface down and then "cover" it back up with dirt after constructing the structure you want below ground. You have linked to an article on NATM, which is a conventional (read: non-TBM) tunneling method.
  - bluGill 2y ago
    Cut and cover often is cover than dig - there are a lot of options
    - abduhl 2y ago
      Cut and cover is what I described: excavate down, build the structure, cover it up. I am aware that there are lots of options, you can browse my comment history and see that I probably have more experience designing and constructing underground infrastructure (and tunnels in particular) than anyone else that posts on HN.
      - bluGill 2y ago
        Cut and Cover is often used in transit conversations to mean any variation where you dig from the surface and not the construction method that is cut and cover. These are two different domains talking about different things that are related. Something we both need to be more aware of in conversations.
        deleted 2y ago
        [deleted]
jeltz 2y ago
Cut and cover only works if your subway follows streets. Yeah, I think we should do that where it makes sense but quite often you need to go under buildings or hills.
- bluGill 2y ago
  Most of the time your subway will follow streets though. Your city has built around the existing streets and people have set their lives up around the places they can get to by the existing streets. If there are two points that are near each other as a crow flies but difficult to reach (shore to an island where there is no nearby bridge) people have made sure they don't need to go there and so you rarely gain much by giving them some new ability. While if you build on the streets they can now go places they were already going via your new subway. Note that I said street and not highway. Some highways (limit access) are good for longer trips, but your subway would be better off using a side street parallel to the highway since while most people use the highway your subway doesn't need to get to any point on the highway while points on the side street - while of limited interest have at least some interest. City transit design is a complex subject that whole books are written about (sadly the people who are in charge don't read them)
  - Symbiote 2y ago
    That seems a very car-centric or American view, with cities built on a grid. Older cities without existing grids can have older metro lines following streets (a limitation of the time they were built, by cut and cover) but newer ones generally don't follow streets. They provide more direct routes, and new crossings over rivers or to islands. Look at Prague or especially Copenhagen for example. https://openrailwaymap.org//mobile.php?style=standard&lat=55.67858860616847&lon=12.583551406860352&zoom=15 https://openrailwaymap.org//mobile.php?style=standard&lat=55...
    - bluGill 2y ago
      Streets have existed since cities began is prehistory times. even before cars people needed to get around.
potato3732842 2y ago
TBMs are for going around problems. Compared to cut and cover you can ignore entire classes of people who would be, expensive, delaying obnoxious stakeholders. <gestures at the contents of an average HN comment section whenever the subject is public infrastructure>
yongjik 2y ago
My neighborhood in Seoul got a new subway line while I grew up, I believe they used cut-and-cover (it was almost at the outskirt, so they didn't have anything else underground) and it took several years. So, while it's doable, it's not exactly "Just dig a hole, build the tunnel and cover, done." It's a major disruption to shops along the street.
- bluGill 2y ago
  It is a major disruption for a couple years.
larsga 2y ago
It's not a choice of TBM vs cut-and-cover. You also have drill-and-blast. Which method is better depends on a number of factors, including depth and the state of the soil/rock you're going through. A problem with TBMs is it can be difficult/costly to secure the tunnel sufficiently against water ingress. If you mess up that one the cost of your tunnel can easily double or more. Here in Norway we recently built a railway tunnel with TBMs (Blixtunnelen) and it's having problems with water ingress. A fairly mild problem relative to how bad these can get, but it's enough that the tunnel constantly has to be closed for repairs to the railway infrastructure due to water drips.
- bluGill 2y ago
  There are many options with different compromises. Cut and Cover comes in many different versions (some of them you build the cover first and then dig under that). However I'm going to double down and suggest that despite the disadvantages everyone else has raised the overall much lower cost of cut and cover, combined with the advantages of a shallower tunnel, makes it the right answer for a lot more situations. Most people claiming to need something else for some local feature are wrong - they can work around that other objection and be better off. Note that I'm not saying the objection is invalid, just that it should be worked around.
  - Symbiote 2y ago
    Are you a tunneling engineer? That over 90% of projects are using TBMs strongly suggests they're usually the better option.
    - bluGill 2y ago
      They are the political option. They disrupt the surface the least and so there are less political objections even though they cost more around the world. Tunneling engineers do what the customer says. They will tell you what the options are and what they cost then let the customer choose the evpensive option if they want. Their job isn't to choose between options it is to eliminate the impossible (unsafe) ones and let the customer choose the pros andecons of the rest.
pjc50 2y ago
Cut and cover is basically unusable in cities because you'd have to "cut" down all the buildings you'd otherwise tunnel under. There isn't some industry saying "yes we could cut and cover here, but we prefer the slower more expensive option of a TBM"! (I see NATM mentioned; there have been safety issues https://www.hse.gov.uk/pubns/natm.htm https://www.hse.gov.uk/pubns/natm.htm ) The HS2 cut and cover tunnels were all in greenfield: https://www.hs2.org.uk/building-hs2/tunnels/green-tunnels/ https://www.hs2.org.uk/building-hs2/tunnels/green-tunnels/ ; much of the cost there goes on planning and documentation, an under-appreciated cost. It's also questionable as to whether they were needed at all; a plain cutting with embankment open to the air would have been fine from a civil engineering point of view, or even in many places just flat track, but the tunnels were planned because people objected to a railway running through fields.
- lytfyre 2y ago
  >There isn't some industry saying "yes we could cut and cover here, but we prefer the slower more expensive option of a TBM"! At least for Vancouver, there was absolutely an industry arguing for the slower-more-expensive TBM option on a route that followed exactly a road (the Broadway line extension) - local businesses along the route. The previous line which was mostly done by Cut-and-Cover (the Canada Line) had a very major impact on businesses along the route for years. There are plenty of people who will acknowledge that something is cheaper _overall_ but the impact on a small group being higher can make them extremely vocal, and that has to be managed in public projects.

rsynnott 2y ago

So it doesn’t seem to be mentioned here, but has there been some major recent change in the economics of the _scale_ of the tunnels? Dublin’s beleaguered metro project recently put out its new design; there are a bunch of changes from the previous early-noughties design, but one of the more eyebrow-raising ones is that the bored sections will now be a single _9.5 meter diameter_ tunnel; it is claimed that this is less disruptive and cheaper than the two-narrow-tunnel approach used in conventional bored metros. Recent metro lines is Barcelona and Madrid have also used the single-giant-tunnel approach. Anyone know what’s going on here? Intuitively you’d expect two small tunnels to be cheaper; you’re moving a lot less material.

timschmidt 2y ago
I suspect the cost is not in volume of material removed, but in operation and maintenance of the machine and it's crew. One tunnel instead of two is half as much machine and crew time.
- freeopinion 2y ago
  Please explain how you reasoned this out. If one 9.5m tunnel requires 70 m³ of removal for every meter of forward progress, and two 5m tunnels requires 40 m³ of removal for every meter of forward progress, won't it take nearly twice as long to dig the single larger tunnel? Won't that require twice the machine hours and twice the crew hours? How does the volume of material removed not directly impact machine and crew costs?
  - jcgrillo 2y ago
    Two dump trucks can't pass eachother in a 5m tunnel. That'll put a restrictive upper bound on material removal rate which isn't present in the larger tunnel.
    - Symbiote 2y ago
      Note they use railway trucks to remove spoil (and transport everything else) from a TBM. A narrow gauge temporary track behind the TBM as it advances.

baumschubser 2y ago

I want to mention a recent extension to Berlin‘s subway system right in the middle of the city, in swampy ground and below a canal. They injected „freeze lances“ into the ground, turned 43,000 m^3 of mud into an ice block and then carved their way through it. Absolutely amazing engineering, I think planned and executed by a Swiss company.

Haemm0r 2y ago
Got a link for this? I am interested :-)
- getwiththeprog 2y ago
  I can find https://www.berlin.de/en/news/8097068-5559700-stabilization-work-u2-tunnel-alex-friday.en.html https://www.berlin.de/en/news/8097068-5559700-stabilization-... Which states that due to sandy soil concrete was injected with lances. It was done by a French company. Might be the same tunnel?
pwarner 2y ago
Big Dig also used ground freezing. https://babelniche.com/2024/01/17/innovations-of-the-big-dig-2-slurry-jacking-freezing/ https://babelniche.com/2024/01/17/innovations-of-the-big-dig... And the Erie Canal dig the sections through swampy ground in the winter. That was partially to avoid Malaria. Circa 1825
padenot 2y ago
This is also a technique that was used more than 100 years ago for the line 4 of the Paris métro: https://www.ratp.fr/en/discover/out-and-about/culture/history-metro-line-4 https://www.ratp.fr/en/discover/out-and-about/culture/histor...
- llsf 2y ago
  Funny that they had to freeze the ground to dig it, as it is one of the hottest line in Paris (at least 20 years ago).

ReptileMan 2y ago

How is The Boring Company doing lately? There will be huge induced demand for tunnels if they manage to deliver even close to their goals.

grecy 2y ago
Slow and steady progress. They’re just about to go big in Vegas, with tunnels the length of the strip.
- youngtaff 2y ago
  The strip is 4 miles long… when Musk company can bore longer, wider tunnels avoiding other infrastructure e.g. London tube lines, sewers etc then they might have something to shout about
  - ggm 2y ago
    I believe he is deliberately targeting low process burden, low soil resistance targets. He isn't aggressively chasing contracts for complex, deep, large tunnels working around existing infra, or rail, he's chasing places which want disruptive change in transport. Nobody has explained to me what the boring company has actually done innovating TBM, the machines themselveds distinct from a cash injection and some energy from Musk as lead investor. TBM are flow process. It's a pipeline of inputs and outputs. It's scheduling. The LV tunnel isn't a complete success either. It's not operating completely as promised yet is it?
DonHopkins 2y ago
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- h3rsko 2y ago
  Its a special "kind of fraud and failure" that launched 90% of mass to LEO in 2024.
  - 2y ago

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ChrisArchitect 2y ago

(2023) Some more discussion then: https://news.ycombinator.com/item?id=37836889 https://news.ycombinator.com/item?id=37836889

kitd 2y ago

Interesting article. This bit was not what I was expecting: Today, rock tunneling machines have achieved tunneling rates of over 700 meters per week, and soil tunneling machines have achieved rates of over 200 meters per week, though this is dependent on the size of the TBM Ie, that rock tunneling can be > 3x quicker than soil tunneling.

ewhanley 2y ago
Rock often has sufficient structural integrity to get by with some bolting vs adding structure (steel, shotcrete, etc) to the soil tunnel as they go
- Gibbon1 2y ago
  It never seems to get stated directly by tunneling through stable rock has to be really easy. Like if you can drill and blast your way through you just need a small crew of workers and a dump truck. There is a half mile long tunnel in the California desert that an addled miner made with hand tools and dynamite over 38 years. Self funded and part time. https://en.wikipedia.org/wiki/Burro_Schmidt_Tunnel https://en.wikipedia.org/wiki/Burro_Schmidt_Tunnel Then digging through unstable rock with water intrusion and danger of flooding the costs have to go way way up.

bilsbie 2y ago

I wonder how far off we are from vaporizing the material and venting it out of the tunnel. Probably way more expensive but you could go faster and don’t need to deal with hauling the material out. It might glassify the surrounding soil and make its own support structure too.

gosub100 2y ago
This topic has been mentioned in regards to digging super deep bore holes for geothermal energy. The high temps a couple miles down started to soften metal drill bits but some companies are working on lasers that are capable of melting rock to allow further digging.
- lightedman 2y ago
  An 80W CO2 LASER is plenty of power. I regularly engrave the living shit out of stone with mine, and that goes a few millimeters deep. Get a couple kW in the same wavelength (10640nm) with a proper adjustable focus (movable diopter) and a galvo and a vacuum assist and you can just start raster-scanning your way through the rock.

bilsbie 2y ago

Has anyone studied how roots tunnel underground so effectively? Maybe we can copy aspects of that.

staplung 2y ago
Yes, they have been. The growing tip of a root is called the root apical meristem[1] but the short story is that they work effectively by being tiny and taking years or decades to develop, so not all that helpful in terms of making things easier or cheaper. They also can't really go through rock, though they can often split them, particularly if they have fractures already. [1]: https://en.wikipedia.org/wiki/Meristem#Root_apical_meristem https://en.wikipedia.org/wiki/Meristem#Root_apical_meristem

yongjik 2y ago

While we're talking about cool boring technologies... I once heard that Seoul's Bus Terminal Station, line 9, was a particularly difficult case. Line 9 had to go beneath existing line 3, but it couldn't go too deep because it (obviously) needed to connect to the rest of the line. In the end they thrust a group of horizontal steel pipes to stabilize the soil and dug beneath it - and those pipes were 15 cm(!) below existing line 3.

abduhl 2y ago
This ground support method is called spiling, for those interested.

extraduder_ire 2y ago

Has anyone attempted to use water jets with aggregate, like you would on a CNC waterjet cutter, for boring through rock? Had this thought the other day and wondered if there would be any advantages over metal cutting teeth. From the article, I gather that replacing cutting teeth isn't that much of a problem nowadays so that mitigates one advantage it might have.