If they had, the neighbors might not have noticed. We blew three 41 lb shaped charges in a VC tunnel and it only sounded like the cap & det cord blew.
Not much evidence on the surface, other than a puff of dirt from an air vent hole. Of course, they were about 75 yards back in from the entrance. But they did blow a nice 8-10 foot hole in the ceiling of the tunnel! :-)
Another question: Does the City of Austin Building Code cover tunnel digging? Do you need electrical outlets every 6 feet? GFCI? Green sheetrock, or will regular 1/2" do?
Zoning codes are some of the most UnAmerican law that exists.
At least on of the “model” codes that is widely copied around the country states in the opening paragraph that anything that is not allowed by the code is illegal, thus setting the standard American philosophy of “anything that is not prohibited is allowed” on its head.