Posted on 02/12/2017 4:26:47 PM PST by janetjanet998
Edited on 02/12/2017 9:33:58 PM PST by Admin Moderator. [history]
The Oroville Dam is the highest in the nation.
Yes. That coupled with the non-uniform sub-base and lack of adequate joint repair tell the story. Failure of this type was certain to occur.
>>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).
If I had to guess, that detail was a last minute accommodation to allow slab placement to happen directly on the rock in certain cases.
Let me opine this: A 15” slab is considerably robust. Interstate paving that I’ve had experience with is but 13”, IIRC. With no reinforcing, save the dowel bars. That particular pavement has been in service for over 30 years, and has held up well.
But let the subgrade deteriorate from water infiltration at the joints, it doesn’t hold up at all.
I have to believe a subgrade failure/washout was the beginning of this event. All the other conditions - cracks, hydraulic jacking, cavitation just exacerbated the failure.
Good stuff.
How do you figure out what needs to be done with the spillway facing south and getting hammered by the sun during the day and the cold nights in that area.
What impact does tons of cold water barely over freezing have on those stress areas when it flows over them?
With highways, joint maintenance is vital. Concrete expands about 2/3” per 100’ with a 100 degree temperature change. Highway blowups (we’ve all seen them) are caused by rocks and dirt infiltrating the joints and preventing expansion.
What I’ve seen the highway crews do is remove the old sealant, clean out the joint with compressed air, then reseal.
With temperature changes, concrete IS GOING TO MOVE. The laws of physics cannot be repealed here. You have to design for that eventuality, and make sure your design is kept up to spec.
The spillway is sited on two very different types of rock, one much softer than the other. Perhaps their thermal properties differed and produced stresses on the spillway.
Here's some "Opine" that echoes strongly:
https://www.linkedin.com/pulse/oroville-dam-our-fathers-legacy-scott-cahill
= = excerpt:
"I become concerned when engineers "watch". Engineers are extremely good at watching. They bring in engineers of every discipline, they put on orange or bright yellow vests, they congregate and they watch. They watch the erosion of the primary spillway. They watch the erosion of the emergency spillway. They put up lights so they can see at night. They monitor the inflows, they monitor the outflows, they pontificate the weather patterns. They are so very thorough when the dam is near failure, what filled their days when it was dry? Were they not walking the spillway, sounding for voids, testing the integrity of the elements, grouting, removing the trees from the spillway?"
"They say things, too. They say that the dam is in no danger, the levies will hold. They say do not listen to those other people who tell you to be concerned. There is no chance of failure. They say that nothing failed. That things are working as they should work. Even that they are unaware of the good men who tried to make them take the steps that would have stopped this evolution of failure (which is not happening, before our eyes). They say the emergency spillway will not be needed, then that it is stable, then that it is about to fail. They say, as they refuse further questions, that they must now go and "protect the people". It seems that the time for action is in the past. It seems that they had their opportunity to protect, a job that they were charged to do, and instead they watched. Now, again they are watching. We all are watching, old people sleeping in shelters, children, mothers and fathers sisters and brothers - watching."
= = end excerpt
KEY Line: "It seems that the time for action is in the past. It seems that they had their opportunity to protect, a job that they were charged to do, and instead they watched." - Scott Cahill
== Another clip from a prior SC article:
"As I write the Oroville dam in California is eroding back toward a breach of the reservoir. I am a dam contractor. If you ever heard someone say "that dam contractor.." they may have been talking about me."
"I have repaired hundreds of dams including ones like Oroville, which were in the process of failure. I know a lot about dams."
"The spillway failure is a common type of failure, where phreatic, or surface water entered the spillway, migrating beneath the slabs. (A static element on a dynamic element, A hard element on a live element). The dam is hydrated and dehydrated as water levels rise and fall, moving, as soils swell from pressures and water mass. In times of high rain the phreatic surface (hydrated soils line) moves toward the surface, venting into the void so produced."
= = end clip
When Minutia overlooks the Macro.... Where is the hard accountability?
In the theme of Atlas Shrugs:
http://www.freerepublic.com/focus/f-news/3524221/posts?page=1918#1918
per sacbee- they hope to have the power plant up and running by mid day tomorrow
at 14,000 cfs when fully operational, that’s about 1/2 needed to handle the snowmelt this spring
“Well it hasn’t failed after all of these times (50kcfs spills)” vs “these may be significant warning signs & potential design issues”.
They weren’t even that rational.
The 2013 repair should simply have been tested at the max flow expected.
Records show it was immediately tested at 7,000 cfs, and then never saw flow over 13,000 cfs in the years up to it’s blowout.
I can see that it would have been very annoying to create a large flow for the spillway during those drought years- but the alternative could only be an unknown risk of failure.
There are some areas I was hearing about this morning that have had about 45 feet of snow that is now 17 feet of snow pack with an estimate 6 feet of water content. When it all gets melting it is going to fill anything it runs into a time or two.
Incredible amount of snow....
pics from today
http://www.kcra.com/article/20-photos-depict-massive-repair-site-at-lake-oroville/9085710
The crane on the left...
I think another item to add is the slope of this large profile pavement. When this thing has a big temp swing at the very steep slope, the forces are much more than experienced by an interstate highway joint. The moving 15” slab with its thermal expansion at the slope that it is at is probably going to really squeeze the joint material.
… discussion:
Looks like inspectors may be doing soundings to get readings on under-slab conditions. Percussion detonations would leave a residue. Seismic recordings from percussions could give useful information (sub voids, acoustic resonance(s), reflection times…). This would be good intel to have in this area as these slabs are closest to the last set that eroded away. The slab on the lower left corner has the most overhang of the undercut erosion. It could be coincidence, but the seams of this slab indicate they have wider gaps. I would suspect there is quite a bit of stress on this slab given its overhang at the end. This slab is also the edge slab where there was concern of hillside erosion threatening the footing of the nearest high tension electrical tower.
Blue lines (just beneath) note angled cracks in the slabs. Seems there are a similar "herringbone" pattern set of cracks here too (angled and in a pattern series).
Another note about the substructure: Close up DWR helo views of the substructure rock under the broken upper spillway edges does not show "bluish" hard bedrock. Pretty consistent of the orange/brown material that downstream erosion (near the blowout area) shows as more erodible. This substructure orange/brown rock is also very deep. I would understand concerns from lower spillway flows & undercutting further. The higher spillway flows had an inertial jump away from the back substructure area. (btw- some of the coloring could be from backsplash of the soil… however, the central area in the middle of the spillway substructure maintains this color pattern of rock. Would find it less probable that a uniform type of soil coating is covering the whole eroded face).
I was able to find a historic color picture of the Quad Cat D9 with dual rock "rippers" attached. They actually were "ripping" rock with these.
See Post 2,120 link here: SUPER QUAD CATS - OROVILLE DAM DIGGING UP HISTORY..
Article noted these "rippers" were used on the main spillway - spoke of replacing rippers due to the heavy rock work.
Uber of Lyft ride for workers.... :-)
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