[HUSSTECH]

I can speak somewhat for the UK, but I assume the same can be said for most of Continental Europe, Japan and China where (deep) underground tunnels for have been around for a long time.

The deeper tunnels of the London Underground are "bored", that is a full circular profile is cut for the tunnel path. This is contrasted with the "cut and cover" method, which just digs a pit, builds a support structure, and covers it back up [1]. Cut an cover is not feasible for deeper tunnels, too much structure is required to hold up the weight of earth above you. Some of the older lines on the underground were dug this way; fun fact: You'll notice in NYC or Boston for example, that the subway stations are all square in their tunnel shape profile, and you can visibly see the support structures, that's because they are mostly not very deep, and used the cut and cover method. I'd be interested to know if any US cities have deeper tunnels? (Despite not being very deep, cut and cover is a very good way to quickly build mass transport for growing cities.)

The BBC has been doing programmes on the Underground for years, so there has been a steady steam of documentaries on this topic! I apologise if you can't get to any of these links:

- A 1969 BBC documentary on the Victoria line (hopefully answers your question 1)^: http://www.bbc.co.uk/programmes/p00sc29t

- A 2014 documentary on Crossrail, London's latest new underground line^^: http://www.bbc.co.uk/programmes/b04bwkj1

^currently streaming in the UK

^^ looks like this one is no longer available, except on Amazon. The Crossrail project website has some info on the show [2], and in general the Crossrail site tires to put educational info on there for the curious [3]

[1] https://en.wikipedia.org/wiki/Tunnel#Cut-and-cover [2] http://www.crossrail.co.uk/news/crossrail-documentary-the-fi... [3] http://www.crossrail.co.uk/construction/tunnelling/meet-our-...

[Nav_Panel]

> I'd be interested to know if any US cities have deeper tunnels

Some NYC subway stations and lines were built with boring as opposed to cut and cover. 90% of the new 2nd Avenue line, for example, is planned to be bored[1]. Here[2] is an article with more details about the tunnel boring machine used -- the comments also have a lot of good discussion. Also, Los Angeles has done some boring for its new subway lines[3].

1: https://en.wikipedia.org/wiki/Second_Avenue_Subway#Construct...

2: http://secondavenuesagas.com/2010/05/14/down-the-rabbit-hole...

3: https://www.metro.net/projects/tunnel-boring-machine-tbm/

[HUSSTECH]

That 2nd Avenue line looks awesome! Also, one BIG thing the NYC subway has over on the London Underground...extensive Air Conditioning! hat-tip

[sethhochberg]

Only in the handful of most recently constructed stations (like the 2nd Ave line, or the new Hudson Yards extension of the 7 line). The overwhelming majority of the station network is 80+ years old and has no climate control.

[Ericson2314]

DC's certainly seems bored—and some are extremely deep and therefore must be. Stations might be cut and cover but are arched to match.

[niftich]

The Washington Post has a good graphic [1] on which stations were cut-and-cover and which stations were bored.

You will find that most stations were actually cut-and-cover, with only the Red Line having bored segments: one starting from after Farragut North [2] and running until shortly after the Medical Center [3], and another starting as soon as it leaves the CSX Metropolitan Sub northwest of Silver Spring and continues until the terminus at Glenmont, although that station itself was built from the surface [4].

Also highly recommend the book 'The Great Society Subway: A History of the Washington Metro' [5]

[1] https://www.washingtonpost.com/graphics/local/wmata-metro-de... [2] http://www.johnreilly.us/washington-metro-transit-design-and... [3] http://www.roadstothefuture.com/Metro_Glenmont_Route.html [4] http://www.nycsubway.org/wiki/Washington,_D.C. [5] https://books.google.com/books?id=beDoAwAAQBAJ

[Ericson2314]

That makes sense. DuPont and Rosslyn are insanely deep; the rest of the orange line, not so much. Thanks for the info!

[jcranmer]

> I'd be interested to know if any US cities have deeper tunnels?

The Forest Glen station on the Washington, DC Metro is deeper than the Hampsted tube station (196 ft versus 180 ft, respectively).

[goatforce5]

Slight tangent:

The world's first tunnel under a river was completed by Brunel in 1843 and is still in use today by Transport for London for as part of the London Overground network (ignore the confusing naming - the Overground is like the Underground, but the service operates at longer intervals).

The Wikipedia page has a lot of detail about how it was constructed:

https://en.wikipedia.org/wiki/Thames_Tunnel

[avuserow]

> I'd be interested to know if any US cities have deeper tunnels

The downtown portions of Chicago's Blue Line[1] and Red Line[2] were primarily dug using tunnel boring machines in the 1940s. Here's a better view of the tunnels being not square[3].

Edit: infographic of various tunnels under Chicago, many of which are even deeper than these bored ones[4]

1: http://www.chicago-l.org/operations/lines/dearborn_subway.ht...

2: http://www.chicago-l.org/operations/lines/state_subway.html

3: http://www.railworks.com/track-project/cta-red-line-tunnel

4: https://uploads.disquscdn.com/images/32697b82560fbd40ec95ec1...