Testing during World War II showed that reinforced concrete is impervious to high explosives. Submarine pens shrugged it off. British Grand Slam bombs acted by deep ground penetration, with the “seimic” waves cracking and undermining foundations.
You are correct, though. The site would be an amusing demonstration of the GBU-57, Massive Ordnance Penetrator (MOP).
“It blowed up real good.”
That is the point of testing on a test site.
If one thing does not work—you try something else.
Lol.