Posted on 01/11/2018 9:52:11 AM PST by bkopto
The principal designer of the spillway told the dam-safety team that he had just completed post-graduate work at the time he worked on the Oroville project decades ago
If he had completed his post-graduate work, he was by definition no longer a graduate student.
I think there is some confusion about the two different “spillways.”
In the report, the young engineer is speaking about the main spillway, not the emergency spillway.
The emergency spillway had never been used and it was basically an overflow with concrete topping in the upper limits. The hillside came apart as water came over it.
The main spillway was used previously and previously repaired poorly. The engineer had completed his undergraduate degree and a post graduate degree. He was not yet licensed and would need to work under a licensed engineer’s supervision for a number of years and then take a test to hold a license. But that is not uncommon, to have young degreed engineers and detailers working under the supervision of a licensed professional.
If the curve and placement of the spillway (main spillway) was designed by the main professional, detailing out the sidewalls and slab could be done by an experience draftsman with supervision by the design professional.
Where one of the main screw-ups occurred was conflict between placing the slab on rock and getting an under-drain placed below it which would have required cutting a shallow trench in the rock everywhere the under-drain would go. Someone, sadly probably this young engineer, approved a detail to thin the slab and not put the drain below the elevation of the bottom of the slab.
This thinning would have severely weakened the slab as if you scored a light thin board 20% of its thickness and tried to break it. It would break right at the score, and that is what happened to the spillway — cracking and future weakening at the location of the under-drains.
There were many other engineering supervisory failures by the Owner. Extra money was not spent to make sure the spillway was not placed on earth or rotten rock when final grading did not expose solid rock to place the spillway slab. Either the Owner didn’t want to pay for the extra cost or the engineering field team did not bring it to a proper decision.
The main spillway was used, not infrequently, and developed problems and those problems were never fully diagnosed or properly repaired by the DWR.
I should probably make clear that they have now spent 500 million to do 70% of the repairs from the last February disaster and these repairs have severe problems.
1.) First these repairs and what will follow this summer do not address (a) structural failures at the gates above the spillway, and (b) the actual earthen dam mass structure seems to have a leak — a “green spot” it is called and these two things are the giants in the room.
2.) The Owner and Engineers designed the new spillway slab and its repair with a special concrete mix and special anchorage bars into the repaired lower sub-grade and rock and these two features were not properly monitored for success by the design team and appear to already have serious cracks, like the original flawed spillway, and may fail in the future despite a half a billion already spent.
3.) There seems to be an effort by California DWR to try and bull past honesty with the Federal certification inspectors and the local media.
These three things are serious issues and have life-safety implications.
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Sounds like you’r3e a Licensed Libidenous Engineer!
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“Rotten rock” (Limestone jumble) is what the entire western slopes of the Sierra consist of.
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Shun hahahhs
Thank you I needed that.
Nope, just a lowly pipe fitter w a little field experience
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License is where you take it!
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What you find in excavating is either competent rock, which is somewhat solid (it all breaks with the right equipment) or you have concomitant rock where the rock (limestone, granite, whatever) is intermingled with other rock or shale and comes apart easily without serving as a bearing layer for your planned construction.
What they found under the spillway when it was removed was some areas of competent rock, but also other areas of weathered shale intermixed with limestone or overburden. The non-competent areas had to be dug out until a good solid base was obtained and then a leveling “mud-slab” of roller compacted concrete was placed so that the final slab would have a uniform sub-base composed of either competent rock or mud-slab place to the planned subgrade of the new spillway slab placement.
I understand your point, that uplifting mountain building tore apart earlier layers of limestone in many cases and plain shelf rock is rarely what you get. But all we are looking for is consistency uniform enough to bear upon.
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Precious little granite on the west side until you get above 6500 feet.
At our place we have a one acre soft limestone bluff above 10+ acres of crumbled crystalline limestone intermingled with crystaline blue SiO2 that is hard enough to burn out a moil point in about two minutes.
It all comes apart with a ripper on a D5 effortlessly.
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