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>>Massive Concrete Chunk: Forensic Main Spillway "Blowout" Failure Evidence?

A Large Chunk of Concrete at the bottom of the Main Spillway may yield clues to the main spillway failure. This sizable chunk of concrete is most likely a "Backfill Concrete" chunk. See blueprint construction drawings (Backfill Concrete) at:

http://www.freerepublic.com/focus/f-news/3524221/posts?page=1830#1830

Why this chunk is so valuable in forensic information is that it reveals critical construction insight. The most important issue this piece reveals is that faulty drainage issues may have been created in their "Backfill" process AND an unforeseen assimilation of gravel in the "top" slab pour.

How? (Here are the important "clues" - indicators): Note: This information is "early forensic data"…

1. This chunk has a flat surface (likely was vertical). The presence of the load transfer "dowel pins" indicate that it adjoined with a sidewall section.

2. This chunk reveals that the top main slab spillway concrete pour was directly on the top surface of this large "backfill concrete block".

3. The irregular bottom of the chunk reveals that it likely was upon a rock surface (thus the need to fill a void to get to the main spillway "grade level").

4. This chunk reveals that there is no observable "drainage" layer or seam (gravel layer) to allow underflow water to be collected into the drain pipes. (i.e. this chunk is solid - layer of concrete on block of concrete).

5. The "flat surface" of this block (item [1]) indicates that the sidewalls were poured first. Thus the the other part of the "void" "backfill" in the flat area of the main spillway formed the flat surface for this later pour (2nd void fill pour in the MS followed by MS top surface pour).

IF 1-5 are correct, there are forensic questions that arise: (A) A vertical "seam" was created that would allow water to penetrate between the two halves of the "backfill". The drainage system design would not be able to capture this water. Water under pressure could go down this seam and below into the lower base rock. (B) If the lower base rock has fractures, the water would continue to penetrate, including laterally deep within the foundation rock. (B) The lack of a "drainage" layer [4] could exacerbate (A). ( C ) Hydraulic expansion and contraction from great spillway forces via the water penetration could further weaken the rock below (penetration into small cracks in the rock). (D) Voids could have formed from gradual crunching of the effects of (A to C). Thus stress would have increased in the main spillway slab, leading to potential or eventual shifting of the surface (heave or slump).

KEY speculation: The fact that the large chunk has the intact remains of the main spillway slab + the concrete backfill is a strong indication of the bonding forces between these two. The evidence of the "seam" + the strong bonding forces indicates that the intended thin gravel drainage layer was assimilated in the top slab pour. This would be critical, as this construction "process" would have messed up the drainage design for the parts of the main spillway. How? Instead of an easy path to drain, high pressure water would have been forced into deeper sidewall seams & the underlying rock. Hydraulic expansion & contraction forces would be problematic.

KEY Point: The "blowout" failure region was noted prior to having "missing" waterflow in the sidewall drains. This "Large Chunk" highly indicates that drainage would not have been optimal (to say the least) in a collecting drain pipe & gravel seam system.

Check out # 2,061 .

For further information, Please read # 2,015 - I meant to ping it earlier...

Here's the link:

http://www.freerepublic.com/focus/news/3524221/posts?page=2015#2015

Thanks, EarthResearcher333.

I guess my comments from a couple of days ago about slab sub-grades not being uniform were correct but even I didn’t expect to see sub-base eliminated by lean concrete slop fill. The hydraulic build up below the slab portions without drainage produced what I speculated was a primary cause of the large failure. Cavitation bubble may have damaged poor joint repair, but they didn’t do this damage.

A concrete forensic detective, our EarthResearcher. It looked like a massive chunk of concrete to me. Earth explains what it all means. Highly recommended reading.

Thanks ER. With the worker-ants in the foreground, you get another perspective about how surprisingly giant this whole thing is.

>>Years of Warnings at Blowout Area? Missing drain water/slabs being repeatedly repaired at leakage..

Where's the water? Apparently there were years of pre-warning signs [2] of an anomaly at the area where the main spillway failed. It is missing water. The main spillway has drain pipes under the concrete slabs that collect any penetrating sub-slab water and route it up into drain outlets in the concrete sidewalls.

btw- Scott Cahill, a dam expert, notes that a well designed/sealed/maintained spillway would have very little drain water during spillway operation [3] (should not be "jets of water" - these "jets" reveal how much volume and pressure the water may "scour" underneath the spillway slabs and substructure rock).

You can see water from these drains from 2013 and in 2017 (just prior to the "blowout failure"). Critically, the "blowout area" has missing water from the drain outlets. This is a critical indicator as a non-presence of waterflow indicates that water is not being collected (possible drain pipe failure) OR the water is not entering the drain either by an improper gravel layer emplacement OR the water has found a deeper flow path (or combinations of all three). Water has been observed to well up from under the main spillway slabs at the area of the blowout failure. The 2013 image reveals this. The 2017 image also shows a "defect" chip in a seam in the main spillway slab (at/near the blowout failure area). This 2017 picture was taken in the last week of Jan 2017, just before the Feb flooding & main spillway failure. Having this defect present would have likely initiated very damaging cavitation erosion from spillway flow (jackhammer effect on the concrete). Likely a precursor to the "missing water" substructure penetration = (i.e. potential sub-structure erosion deep under the slabs or undermining the "backfill concrete" chunks [1]).

= = reference notes:

1. Stagnation Pressure' as described by the Bureau of Reclamation: "Stagnation pressure refers to two conditions that can result in damage and/or failure of the spillway: (1) High velocity, high pressure flows enter cracks or open joints in the spillway flow surface (such as a chute), which results in uplift pressure that lifts (displaces) portions of the spillway conveyance feature; and (2) High velocity, high pressure flows enter the foundation through cracks or open joints in the spillway flow surface, which results in internal erosion of the foundation and loss of support of portions of the spillway conveyance feature [26]."

2. Alarms Raised Years Ago About Risks of Oroville Dam's Spillways:

..excerpt: "The cratering of the main spillway — which spiraled into the current crisis in Butte County — occurred in a spot where cracks and other defects had been found repeatedly since 2009, said Robert Bea, a professor emeritus and engineering expert at UC Berkeley." “My God, we had evidence that there was trouble going back to 2008, 2009,” said Bea, who at The Chronicle’s request reviewed 14 dam inspections from 2008 to 2016 conducted by the Division of Safety of Dams, which is part of the Department of Water Resources.

“Yes, they had detected the defects (in the main spillway) and yes, they had put into gear remedial measures,” Bea said. “Were those repairs sufficient? No. The result was a breach.”

.. end excerpt

http://www.govtech.com/em/disaster/Alarms-raised-years-ago-about-risks-of-Oroville-Dams-spillways.html

3. One highly respect dam design expert, Scott Cahill, had some very enlightening information regarding Oroville's main spillway & issues linked to his extensive knowledge on dam failures. Three of the key issues he noted in detail was (1) thorough & expert level maintenance (2) the Oroville main spillway had too high of an underflow of water beneath the concrete [as he noted by the amount, volume, and velocity of the "jetting" underdrains - this is a significant issue to address to prevent erosion scouring and sub-spillway pressurized leakage] - [i.e. this was an "early warning" that should have been taken action upon] (3) the original construction MUST be thorough on its bedrock/concrete and anchoring stability.

Workers in 2013 at pre-failure blowout area - notice the missing drain flow (red circle) and the notable upwelling of water in the main spillway.

Same missing waterflow in drain near pre-failure blowout area. notice the defect in the concrete slab seam at/near the pre-failure blowout area.