Remember the "Mother of all Battles?". That is typical bluster and hyperbole.
The strength of the concrete just guarantees a stronger, more permanent tomb. The achiles heels of any facility is the access, the entrances. destroy those and everything else is irrelevant.
If the facility itself can't be penetrated by large bombs, the interface with the original terrain is not. Ever try to open a door with 100 tons of dirt stacked up against it?
There is no protection that the mind of sandmaggots can devise that the minds of normal free people can't circumvent.
"Fortifications are monuments to the stupidity of Mankind." General George S. Patton