When I saw detail “A” in post 2132 I said to myself I would shoot one of my civil staff for detailing something like that. It goes right back to that faulty slab on solid rock issue I have whined about in previous posts.
Detail “A” facilitates a weakening of that slab right along that drain pipe by thinning the slab. If the slab had sub-base rock below it, the sub-drain should be put in a french drain channel below the layer of sub-base rock. Having it run slightly diagonal down hill is a sensible feature that they made in the field but having no uniform sub-base with this drain below the sub-base is substandard in my thinking even for the 60s.
Here is the drawing that detail was from.
https://www.usbr.gov/tsc/techreferences/hydraulics_lab/pubs/HYD/HYD-510.pdf
pg 172 of 193
dwg A-389-4
>>When I saw detail “A” in post 2132 I said to myself I would shoot one of my civil staff for detailing something like that....
Yes that seems odd to weaken the design.
-— note: discussion only:
This begs the question(s): With all of this mounting evidence and information (many posts & discussions in this thread..), what did the Maintenance, Inspectors, and Engineers in charge of the dam think of all of this?
With the detail “A” information, the herringbone type pattern of cracks being patched, the volume of water jetting out of the drains, and the non-operating two drains, this should trigger the same type of reaction you mildly proffered.
Complacency? This was about the 10th time the spillway was operated at/near 50,000 cfs (before this 10th operation & “blowout”). It could be that that there were big concerns and requests were made for major repairs? I can see both sides of the discussion. This is a classic case of engineering “judgement” where one side could say “Well it hasn’t failed after all of these times (50kcfs spills)” vs “these may be significant warning signs & potential design issues”.
The same circumstances of “sides” of an engineering debate led to the Tacoma Narrows Bridge collapse. One side said that prior other suspension bridges, of that architecture hadn’t failed, while the other side said that the Tacoma bridge is not conservative enough. (came down to “beauty of the thin design” vs the “uglyness of gaudy conservative over design”). Turns out, the other suspension bridges that were referenced HAD the same airflow oscillatory defect. It was just that these other long suspension bridges had NOT experienced the persistent transverse windflow that exposed this defect (in the Tacoma Narrows Bridge).