Out of curiosity I tried some of these suggestions. My current game I’m playing mostly underground in a network of subways, and it would be nice to put a water well in a couple of places.
Testing on rock floors and concrete floors underground, I wasn’t able to dig a pit using some of these suggestions. It was not possible to lay carpet down, or install much of anything as far as walls / fences except a stone wall. But you can certainly get a pit destroying certain kinds of wall if you have them available (for example in a lab). I tried doing something similar in the surface minus one level of a subway station, but it doesn’t work there.
There are still basements with dirt floor sections you can find though. And a mole rat can transform floor to dirt when destroying stuff, you might be able to use that creatively. 8)