was the (one of) the very person(s) who sat and argued against these types of bases last year with me on this very forum.
Make up your mind. Are you attacking the tunnel or the entrance? Attacking the entrance isn’t going to collapse the tunnel especially with that blast door in place. (Let’s assume no special mesh overhanging the blast door entrance during war time).
It isn’t as simple as carving a cavity into the mountain. They are reinforced with special type of concrete and there is a thickness between the mountain-rock and the ceiling of the tunnel.
If you try to hit a major part of the tunnel (to collapse it) you have to first pierce thru the mountain since hitting the entrance cannot trigger such a collapse. Thus you are going thru deeper bedrock (more inside the base). If successful then you have to past thru the reinforced elements that are there to stop such a collapse. If successful going thru all of after, then explode to try to trigger an integrity collapse.
At best you would need one of the biggest/strongest bunker buster in USAF arsenal, at worst a tactical nuke. No guarantee of success.