Make no mistake, American excavations have archaeologists monitoring operations to make sure relics don't get destroyed. Bak in the late '70s, when my mom was an anthropology student, she took part in digs at sites found when MARTA was coming through. Mostly trash piles -- you can learn a lot about people by what they threw away.
There was also an ancient find that temporarily halted construction of a high-rise condo a few years back -- I don't remember the details.