21 k tons of conventional explosive.
Probably killed the worms in the ground a half mile round.
Might have collapsed shallow tunnels.
Might have collapsed the entrances of deep tunnels.
Might even have sent a fatal shock wave rolling down the length of otherwise undamaged tunnels .
Shouldn't be long before we know.
If the killing effect was effective as it might have been, there will not be much defense of these tunnels.