ER333: you always have interesting, well researched, and thought-provoking posts. Again, many thanks.
Regarding the concrete chunk you reference, Bill Crowle from DWR did say that the spillway slab was 6 foot thick in sections, and that chunk does appear to be from one of those extra thick sections.
On one hand, I’ve worked enough construction to know that no contractor will lay down 6 feet of concrete if they can get away with a 1 foot slab on top of whatever type of (erodible) base material they were using. The contractor pays for every truck load of concrete, and that comes out of their profit margin, which they’re generally rather concerned about. This would be an argument for there being a 1 foot base slab, with the rest mud jacked in years later, as you suggest.
On the other hand, from the picture, the entire chunk of concrete appears monolithic with the same mix design, and I couldn’t see two lifts of concrete placed a couple decades apart tumbling 1000 feet downstream as a monolith. I think we’d need a closer examination of that chunk of concrete to make the call.
If they did mudjack the slabs, it seems plausible this could plug up some of the diagonal under-slab drains. However, I couldn’t see this plugging up the longitudinal side collector drains. This would be too easy to check for, even in the pre-borehole camera era. You just pour water down the upstream vent tube, and if it doesn’t come out the downstream sidewall port at the same rate, then you know you have a clog between the two. DWR may not be the sharpest crayon in the coloring box, but you’d have to be a total idiot to let a spillway contractor walk away from the job with a paycheck without checking for a clogged drain.
If a tree root was a contributing factor to the drain clog which precipitated the spillway failure, and we know the drains were under high pressure, then it seems plausible that the pressurized water could escape along the root pathway through the fill to the side of the spillway. This would provide a high-volume escape route for the water, taking more more base material with it. Some pictures appear to indicate the side of the spillway was blown out before the major slab failure.
If the pressurized water had no escape, it would push the slab up, “hydraulically jacking” it. If the water had an escape route, it would go longer be pressurized and spurting out the sidewall, but eroding underneath it, and the slab would fail downward. Up or down, the slab failed one way or the other.
A contributing factor to both the spillway failure and FCO structure problems which hasn’t been examined in this thread (to the best of my knowledge) is concrete shrinkage. Some old mix designs would shrink quite a bit. With the extra large slabs they were using on the spillway, the expansion joints could pull apart, letting more water under the slabs than could be caulked out. This could also contribute to why FCO is now 5 1/2 inches shy of the fixed foundation at the abutment, and cracking at the seams.
To build a R/C structure and that needs to function reliably for a 100 years or so, I’d go with an expansive mix design, using a type K cement. This has Ettringite (calcium aluminum sulfate) added. There are type K slabs which are approaching 50 years old, the same age as Oroville, that are still in almost perfect shape with no cracks or joint issues.
A plausible hypothesis as to why a tree root may have grown adjacent and then into the drain at the blowout failure location is that there was a natural “Water Percolation Seam” at this location. The native geology of the area appears to contain a great deal of fractured and erodible rock with many fissures that water could percolate through. It is also plausible that such a seasonal “Water Percolation Seam” could be injecting moisture into the side of the dam, creating the (apparently) seasonal “Green Spot”.
If you want a high level technical discussion - rise to the level of the body of research and thorough evidence in totality and fully recognize the body of what has been researched and presented. Otherwise I would rather not engage.
Given this, let's just take one issue at a time.
Let's leave out "crayons", and "idiot contractors" getting paid while assuming they were supposed to do something...euphemisms.
Did you read post 3705? Where the DSOD Inspector stated they found voids in the spillway by "soundings" (drummy patches)? Did you read the following statement by the DSOD inspector "No treatment is proposed until they are damaged by a heavy flow"?
(1) The cavity size to create a "drummy" echo sounding on the spillway concrete has to be of enough significant "void" volume to provide the dB acoustic response back through concrete to be heard. Do you agree or disagree? (yes/no)
(2) The DSOD Inspector found more than one area (acoustic drummy patches) that generated the significant enough dB acoustic response back through the concrete to be heard and noted. Do you agree or disagree? (yes/no)
(3) The DSOD Inspector identified that an action ("treatment" and/or remedy) was only going to be acted upon "until they (acoustic drummy patches) are damaged by a heavy flow". Do you agree or disagree? (yes/no)
(4) If DSOD - the Inspectors, who should be identifying the corrective actions that should be taken to the dam owner/operators (DWR) - are being told that "nothing will be done until these areas are damaged", does this in any way identify to you that something is severely wrong with the curtailing the authority of the Inspectors? Do you agree or disagree? (yes/no)
Thus, would this give you any indication as to the pattern of operations and decisions that identify how serious problems develop and are not effectively investigated by DWR/DSOD - agree or disagree?
You say jpal: "Bill Crowle [sic] did say that the spillway slab was 6 foot thick in sections,..."
Yet you provide no proof to 6 feet in Bill Croyle's statement. In fact, the only information is a 4 foot to 5 foot value from "coring" of the Upper Main Spillway. (see information from metabunk where Dan B. contacted DWR to get further details): (https://www.metabunk.org/oroville-spillway-investigation-and-repair.t8640/page-3)
- - metabunk clip: I asked DWR the week before last to expand on the claim about the thicker concrete. Here's part of an email exchange with the person who's been put in charge of responding to most spillway questions:
Q. Director Croyle mentioned that drilling on the upper spillway has revealed areas with 4 or 5 feet of concrete. How extensive are those areas? Earlier reports from Board of Consultants and others stated the slab was 9 to 15 inches thick (depending on placement of sub-slab herringbone drains). Were those reports essentially accurate?
A. A number of holes have been drilled in the upper portion of the gated flood control spillway and more will be drilled in order to assess geological conditions. Some bore holes show concrete that is four to five feet thick, some do not.
And that's all the department's communications apparatus chooses to say on that subject. I don't know if you could be less informative if you tried, but I'm guessing that's precisely the department's intention. It would be easier if they'd just say "take our word for it."
= = end clip @ metabunk
Given this, you claim: "..and that chunk does appear to be from one of those extra thick sections".
So how did the Upper main spillway suddenly break off a chunk and hurl itself down to the end of the bottom of the Main spillway without anyone noticing? AND while it was on the way down, this chunk, after being "cored", grew to 7.5 feet in thickness?
You see... I can disassemble your reasoning & statements swiftly.
Bill Croyle's 4ft to 5ft statement was a PR response to pressure from the thin design issues & proven thin areas of the near 5 linear miles of cracked drains. Did it ever enter into your thinking that the thickness of the slabs, when recently cored, may have been affected by all of the "void" filling that has been going on for years in the pressurized erosion washing conditions under the spillway? OR was it possible that the 4ft to 5ft coring thickness statement was from testing the Upper Main Spillway sidewall footings? (a highly deceptive answer in a PR sensitive distrust of DWR).? I could continue to disassemble the rest of your reasoning & statements in the post. But I will wait to see how you answer on all of these post items.