^it's no problem at all for a competent builder to dig under an existing structure. Though many others have collapsed buildings by attempting to do it the wrong way, or too fast.
There are only a couple builders in Hamilton experienced enough to reject the commonly accepted notion that it's impossible to excavate below a single storey in Hamilton because of water below the surface.
Outside of deserts, what city doesn't have water just a few feet under the surface?
Toronto's Union Station recently received this treatment while Canada's busiest train station
continued to operate above.
Illustration of the column replacement process for the Union Station dig down project, image supplied by NORR Architects to http://urbantoronto.ca
Why aren't these workers in SCUBA gear, I wonder?