^ You don’t need to expropriate homes to go underneath.
Except, actually you do.
(You don't need to TAKE the whole house, but you most definitely need to compensate the owners because, just as we think of air rights, you own everything above and below your property,)
Best reference I could find quickly was this one, from Ottawa.
EDIT: And just for overkill, here's another one, from a Provincial regulation about temporary easements, in this instance, and by Metrolinx.