It was built at an accelerated pace - obviously - and one of the issues with that is the cement is still curing. After nearly 60 years? I wouldn't have believed it, had I not spoken to the PM running a project on it.
The project? They were taking a slice out of the dam. Top-to-bottom, all 400-odd feet. The cut was roughly an inch thick. Would make room for expansion due to the curing.
Struck me as a massively bad idea to cut a hole in an active dam, but here they were doing it. I sat there for an afternoon, watching a crew of workers on scaffolding and ropes, scampering across the face of the dam. Wouldn't have believed it had I not seen it with my own eyes.
Haven't read where it ruptured, and like I said, it's been about 20 years, so I'd think that if something was going to happen, it would have by now....
The concrete in Hoover Dam is so thick it would have taken 125 years for it to cure naturally. They installed 585 miles of 1 inch pipe in the concrete to remove the heat from the exothermic curing reaction. That sped up the curing a lot.