[hinkley]

For instance, the first subway systems in London were installed via cut and cover. Dig a trench, build a roof. Usually those trenches were in the street, or a former canal, not under a building.

Using modern tunnel boring equipment, Seattle's attempt to move the downtown section of 99 into a tunnel ended up stalled for a year because the ground shifted and pinched the boring machine in place. Oopsie.

And of course if you're worried about gasses, puncturing a solid piece of concrete is just going to make that problem worse.