Well, Imagine That? A Countermeasure.

We develop a 30,000 pound Massive Ordnance Penetrator (MOP) GBU-57A/B, and the Iranians develop a super tough concrete that should neutralize the threat:

A DUAL-USE technology is one that has both civilian and military applications. Enriching uranium is a good example. A country may legitimately do so to fuel power stations. Or it may do so illegitimately to arm undeclared nuclear weapons. Few, however, would think of concrete as a dual-use technology. But it can be. And one country—as it happens, one that is very interested in enriching uranium—is also good at making what is known as “ultra-high performance concrete” (UHPC).

Iran is an earthquake zone, so its engineers have developed some of the toughest building materials in the world. Such materials could also be used to protect hidden nuclear installations from the artificial equivalent of small earthquakes, namely bunker-busting bombs.

It appears that, among other things, it is quartz powder rather than sand that is mixed in, and polyethylene fibers are added, which further improve impact resistance.

It appears that this would reduce the penetrating capability of the MOP from 40+ meters to less than 8 meters.

We're going to see a lot more of this going on from potential opponents, because our military has become increasingly dependent on high tech gizmos, as opposed to people, which limits the tactics that can be employed. This means that avoiding any countermeasures that a determined and intelligent enemy are likely to develop, and they are all likely to be both, and so the the countermeasures are both easier to devise, and more likely be a effective.

Overspecialization, the Devil's volleyball.