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Comment by tobylane | Hacker News Reader

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.

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> 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.

It also resulted in a rail line that has to slow down significantly to round screeching curves along the path of the road above.

> 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.

> 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

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.

I imagine it's also a bit difficult to separate it this cleanly, as most bigger projects will probably use a mix of technologies: cut and cover where possible (if it leads to savings), TBMs or other technologies like NATM (https://en.wikipedia.org/wiki/New_Austrian_tunneling_method) for the rest. Even if TBMs are used for the tunnels, cut and cover will probably be used for things like stations, emergency access points and intermediate TBM starting points (of course, the TBM starting points might be future stations).

Combining is an option. However a large part of the cost of TBM in the initial get it into place and then when you are done taking it out (sometimes you just leave that expensive machine down there). Thus if you must use a TBM the farther you can go in that one dig the overall cheaper the tunnel.

> I imagine it's also a bit difficult to separate it this cleanly, as most bigger projects will probably use a mix of technologies

Case in point – the Karlsruhe tram tunnel (listed in that dataset as simply "Tunnel Boring Machine") used a tunnel boring machine for the main east-west tunnel, but a combination of NATM and cut-and-cover for the north-south branch. The stations and the associated road tunnel project were all cut-and-cover, too.

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