This might help:
http://www.icwdm.org/handbook/carnivor/ca_c1.pdfI know you asked about trapping, but the other thing that has been tossed about before is throwing in a loud firecracker, the louder/bigger the better, and wait for the critter to come boiling out of that hole. And a shotgun in hand should render that badger harmless when it comes to the surface.