urbanMSP

One concept that frequently comes up during when discussing hypotheticals in the transportation forum is the idea of "cut and cover" tunnels for LRT. I wasn't familiar with this concept until recently, though by the name I can pretty much figure out what it means.

However, since it just came up again in the Nicollet Mall discussion, I'm hoping to foster a general discussion here. There are two questions I'm hoping can be answered here:

A. What is it about a cut and cover tunnel that makes people talk about them as if they are a truly realistic option? Is it just that they are cheaper?

B. If cut and cover tunnels are truly realistic, how come it seems like there is little actual talk about them among transportation planners? Still too much money?

I don't think there's anything particularly special about cut-and-cover. It's typical of how a shallow tunnel would be built -- it just requires digging a huge hole in the ground to pull out all of the dirt, stone, and whatever else might be under there (utilities in modern cities) and then start building a tunnel casing which is eventually all covered up with dirt again. Sometimes the top of the tunnel ends up underground quite a ways, or it might only have a thin cap on top, like a bridge or the deck of a parking structure.

You could try to bore underneath, either with a machine made for the task (TBM) or using more manual methods. But it's probably a lot faster and less of a collapse risk to just dig up a whole street to build the tunnel rather than trying to inch your way underneath a busy area. But of course cut-and-cover has a more obvious disruption for residents and businesses.

I tend to think of the I-94/I-35E commons in downtown Saint Paul as a cut without the cover, since it has such vertical walls on the sides. I know the airport tunnels for Hiawatha LRT were made with a combination of cut-and-cover and TBM-bored tunnels (TBMs are also very long machines which need large "launch boxes" to be carved out of the ground, which often aren't practical in denser urban areas).

http://railsystem.net/cutandcover.htm

Breakdown of what the cut and cover construction process involves.

Just a thread for everything about tunnels and tunneling. International, national, local... rail, road, anything else...

Looks like Elon Musk is taking his mysterious tunnel tweets to a new level.

https://www.wired.com/2017/01/inside-tu ... s-angeles/

Maybe Musk will invent better tunnel boring?

He very well might, but I'm reasonably sure that the reason we don't have subways everywhere is that it would take too long to dig the tunnels. Boring speed isn't the limiting factor.

A PBS documentary on the historical push to get rail lines underground.

http://www.pbs.org/video/2365945692/

Turns out the blizzard of 1888 was the biggest trigger, dumping many feet of snow in places shutting transportation down all over.

The Daily Mail on Elon Musk's tunnel boring story.

http://www.dailymail.co.uk/sciencetech/ ... chine.html

What a boring story! Why share it??? Zzzzzzzz

*rimshot*

Like hyper loop and self driving technology, this tunneling nonsense will only look feasible if the most challenging aspects are ignored.

Tunneling isn't nonsense in Seattle right now, at least for transit rather than SR99.

Yes, but musk and his fanboys won't revolutionize tunneling.

Seems like a good time to readdress my [admittedly bonkers] deep bore I-94 plan. Hmmmm...

Angie Schmitt at Streetsblog really down on Musk's idea of tunneling to reduce highway congestion.

http://usa.streetsblog.org/2017/02/07/e ... idiculous/

With bonus call out to a streets.mn blog post about thoughtful legislation.

The assumption seems to be that Musk wants to tunnel for roads (highways), when building more subways is the far more practical and likely result of any tunneling technology improvements.

I think I agree. Seems he's using his tweets to drum up interest in general. In the way that everyone assumes discussions around reducing congestion must mean getter options for getting around in cars. There could be a fair chance this won't involve cars.

This isn't specifically about tunnels, though tunneling costs make a major point of the article. Alon Levy writes in The American Interest, "Why We Can't Have Nice Things". His thoughts on why infrastructure costs are so high.

http://www.the-american-interest.com/20 ... -things-2/

Many have looked at why US costs are so far above other western nations, in this he points attention at early 20th century reform laws that solved problems with corruption and graft. He believes that today there are better ways to conduct oversight that doesn't have to slow things down and cost as much.

Another week and more about Elon Musk's "The Boring Company" has another profile.

Musk says he hopes to build a much faster tunneling machine and use it to dig thousands of miles, eventually creating a vast underground network that includes as many as 30 levels of tunnels for cars and high-speed trains such as the Hyperloop.

https://www.bloomberg.com/news/features ... lly-boring

Well, that answers Tiller's question about why everyone assumes that Musk is talking about tunnels for cars.


And also confirms that he still is under the impression that the limiting factor on infrastructure construction is "ability to construct the infrastructure".