6 ms·

You don't necessarily even have to tunnel, like one would do with a borer. I think that would be cost-prohibitive. Trench and cover, probably with streets. Bu

You don't necessarily even have to tunnel, like one would do with a borer. I think that would be cost-prohibitive. Trench and cover, probably with streets. But it would create a lot of extra void to maintain that would need its own drainage, maintenance to keep it free of debris and pests, inspections to make sure they don't collapse, and security to keep people out. Feasibility is probably commensurate with urban density.

bobthepanda 5y ago
There's also the issue of where you would put all the spoils from tunneling. Historically that was in the ocean and rivers to make more land, but this is frowned upon for a variety of reasons now, the least being that not all types of soil work well as landfill.