Directly above? above the entrance? Yes the explosion can be powerfull enough to make the entrance collapse... but It is better to use conventional explosives for this purpose.
Airbursts don't have good cratering effects, so they won't destroy a tunnel network
This is what i want to explain, If a nuclear detonation happens in such a way that the long term effects are minimised they will have the same impression as of A conventional explosion just many times powerfull.
The problem while dealing with hardened military targets and as you have said...