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
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.
> 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.
> What projects in developed countries have used cut and cover recently?
Not really a new project, but parts of the subway in Stockholm are cut and cover. One of those tunnels (from the 1930s) has been leaking in water for some years and is up for a total overhaul, so basically digging up everyting and doing a new cover.
The section is 8 m wide and 925 m long, projected timeline is 6-7 years starting this fall. It will be a massive project, as one of the busiest streets in Stockholm is directly on top of it.
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.
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.
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.
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.
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.
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)
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).
The HS2 cut and cover tunnels were all in greenfield: 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.
>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.
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.
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>
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.
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.
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.
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.
Two of everything, ventilation, electrical, water,
telecoms,you name a system, and then name it again.
Chances are that set backs required for engineering and existing infrastructure will be
challenging, with two parallel sytems.
edit: there is an assumption that the space required undergroud is free and infinite, when in fact two tunnels with set backs and spacing will require more total space than one larger tunnel
and will then limit the availible area for deep building foundations and anything else.
Then we get to interchandes, and emergency access.
And there is a ready market for any material removed from the dig, which will be a very routine operation.
And while the volume of fill removed will be greater, the internal volume per cubic foot of tunnel wall will also be greater, allowing for more generous alotment of space for future systems and untilities, bigger wider lanes, etc.
Somewhere I came across a journal, just for tunnel makers, and there equipment.
And recent reports have tunnels bieng completed
ahead of schedule and on budget, so they are infact, taking care of business.
Oh, yep, I’ve no doubt that if they can ever actually get planning through for the damn thing, they’ll be able to build it. In Ireland it’s generally the planning that’s the problem.
What I’m curious about, though, is what, if anything, changed to make this single-bore approach suddenly popular. A lot of new metro lines seem to be built that way, but old (and not, like, 19th century, even most 20th century stuff) always seem to be double-bore.
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.
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?
Is there any reason to think they will be able to? They are just going the same thing as everyone else but started later. Another player might lower costs slightly but not much.
I don’t believe they have advanced the field in any way. They didn’t really have any solid ideas, just the idea that it would be really cool if tunnelling could be made cheaper. Surprise surprise, it’s actually a highly advanced, mature field and there wasn’t actually any low-hanging fruit for inexperienced startup guys to disrupt…
The only thing they’ve done with their Vegas tunnel is to make it cheaper by making it too small to have proper emergency egress, but they can get away with it since with just their chauffeured Teslas going through it only fitting a few people each (making the system extremely low-capacity), they can’t really fit many people in at once, and it’s short enough so combined that makes it not that much of an issue.
In the newest section of the Vegas tunnel they have now only built a one-way tunnel instead of a tunnel for each way, making it cheaper again but low-capacity to a basically comedic level.
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
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.
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.
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.
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.
Readit News
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
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.
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.
Not really a new project, but parts of the subway in Stockholm are cut and cover. One of those tunnels (from the 1930s) has been leaking in water for some years and is up for a total overhaul, so basically digging up everyting and doing a new cover.
The section is 8 m wide and 925 m long, projected timeline is 6-7 years starting this fall. It will be a massive project, as one of the busiest streets in Stockholm is directly on top of it.
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
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.
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.
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)
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 )
The HS2 cut and cover tunnels were all in greenfield: 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.
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.
(better translate from the german version, as it has more information and examples)
<gestures at the contents of an average HN comment section whenever the subject is public infrastructure>
Coolo, you are building tunnels in a city that doesn't exist yet.
Start here - 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.
And the Erie Canal dig the sections through swampy ground in the winter. That was partially to avoid Malaria. Circa 1825
Which states that due to sandy soil concrete was injected with lances. It was done by a French company.
Might be the same tunnel?
Anyone know what’s going on here? Intuitively you’d expect two small tunnels to be cheaper; you’re moving a lot less material.
What I’m curious about, though, is what, if anything, changed to make this single-bore approach suddenly popular. A lot of new metro lines seem to be built that way, but old (and not, like, 19th century, even most 20th century stuff) always seem to be double-bore.
How does the volume of material removed not directly impact machine and crew costs?
Some more discussion then: https://news.ycombinator.com/item?id=37836889
The only thing they’ve done with their Vegas tunnel is to make it cheaper by making it too small to have proper emergency egress, but they can get away with it since with just their chauffeured Teslas going through it only fitting a few people each (making the system extremely low-capacity), they can’t really fit many people in at once, and it’s short enough so combined that makes it not that much of an issue.
In the newest section of the Vegas tunnel they have now only built a one-way tunnel instead of a tunnel for each way, making it cheaper again but low-capacity to a basically comedic level.
Dead Comment
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.
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
Then digging through unstable rock with water intrusion and danger of flooding the costs have to go way way up.
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.
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.