TFA's picture of the failed spillway is hilarious. That concrete can't be more than 4 inches thick! That would work for a driveway, barely. It seems really out of place on a giant dam. As soon as there was a crack, the underlying gravel and earth would start eroding, and a complete failure like that pictured was inevitable.
6-8 inches is terribly wasteful and a bit of a nightmare for anyone following who wants to fix a pipe. Obviously a thick path is needed sometimes, but 8 inches will take a 10 ton truck just fine.
Because they are arguing from being smart in a different field and experience with things that are several orders of magnitude off the scale of what they're dealing with.
Things that work on a laptop with the dev server don't work at scale, and you won't even understand the problems till you've had some theory/experience with the problems that scale adds.
At a guess because they have no experience or knowledge on dimensioning something made out of concrete.
You can land an A380 on a runway 17" thick...
This was definitely strong enough, just not ready to withstand cavitation and given that bronze ship screws suffer from it it is hard to see what kind of liner would have solved this problem entirely.
Solving it completely may ask for a totally different design, likely not a different material or thicker concrete.
I'm not sure you saw the scale of that spillway. It is _massive_. Something like 300ft wide and 3000 feet long. An entire football field wide. It's quite obviously not 4 inches thick, but admittedly at the scale of it, 15" doesn't seem like a lot.
The scale is deceptive. Take a look at the report on this
https://www.youtube.com/watch?v=5xa_Q1R7mGs&t=132s and you will see a thick concrete spillway with 1.5" rebar. All that was ripped off by the force of the water!
The scale is very deceptive. The estimates are a million cubic yards of erosion and repair bill of about $250 megabucks. Of course, the smart move isn't to fix it exactly back to how it was exactly but to engineer the most value/$ TCO fix with the least cost and effort.
There's probably 20 Hoffman-crew-sized rented vehicles, and subcontracted employees and value-add diesel fuel ain't cheap either. It's going to take probably 9 months, at a minimum.
