CA Department of of Water Resources says: “don’t worry”, it’s “robust”.
Readers may recall that in February 2017, the spillway at Oroville dam eroded and collapsed due to the massive amount of water from El Nino weather pattern induced storms eroding concrete that had cracks in it that had not been properly maintained. The state DWR agency spent an estimated $500 million to rush a new spillway replacement into service by November 1st. Now it appears this rush job has cracks in the steel reinforced concrete, repeating the same start of the scenario that caused the collapse in the first place.
From ChicoER: Small cracks have appeared in the new concrete in the main spillway at Oroville Dam, but the state says they were expected and nothing to worry about.
An explanation of the “hairline cracks” was called for in a letter the Federal Energy Regulatory Commission wrote to the Department of Water Resources in October. KQED radio in San Francisco first reported the previously undisclosed letter Tuesday.
The Oct. 2 letter from FERC said it understood DWR was concerned when the cracks were discovered after concrete curing covers were removed from some of the slabs poured this year.
It called for a report within 30 days that mapped the cracks, identified potential causes and spelled out remedies, “if necessary.”
The state has been rebuilding the spillway after most of it eroded away in February.
KQED also reported Tuesday on the cover letter to the DWR report submitted Nov. 7 in response to the FERC letter. The actual report was not available.
In the cover letter, DWR said it had evaluated the cracks and determined they were caused by efforts to create “a robust and durable structure.”
…
“With the inclusion of these design elements, the presence of hairline cracks was anticipated and is not expected to affect the integrity of the slabs,” DWR said.
Yeah, sure. Full story here.
From KQED:
UC Berkeley civil engineering professor Robert Bea, a veteran analyst of structure failures, said cracking in high-strength reinforced concrete structures is never expected.
“Cracking in high-strength reinforced concrete structures is never ‘to be expected,’ ” Bea said in an email. Even small cracks could increase stresses in the concrete when it is under “service loading” — for instance, when large volumes of water hurtle down the structure at speeds approaching 90 mph.
The cracking “develops paths for water to reach the steel elements embedded in the concrete and accelerate corrosion,” Bea wrote in an email. “Such corrosion was responsible for the degradation and ultimate failure of the steel reinforcing in parts of the original gated spillway.”
DWR inspection and repair records going back to the 1970s documented widespread cracking of the 3,000-foot-long spillway chute — largely because of the thinness of the concrete covering the drainage system below the concrete slab. On at least two occasions, sections of the steel rebar inside the slab were found to be corroded and in need of replacement. After the spillway failed last February, some of the steel rods intended to anchor the slab to underlying rock were also found to be corroded.
more at KQED here at their website
And here is the audio report:
Documents:
https://assets.documentcloud.org/documents/4311073/FERC-DWR-Oroville-Concrete.pdf
https://www.documentcloud.org/documents/4311072-DWR-FERC-Concrete171107.html
Thsus begins the Battle of the Structural Engineers. In this corner, the state engineer attempting to
explain these “normal and expected” cracks and in the opposite corner the skeptical professor.
Stay tuned for further developments.
i foresee a hundred thousand dollars of epoxy in oroville’s future
Government work in Cali is all that it is cracked up to be i guess…
…Readers may recall that in February 2017, the spillway at Oroville dam eroded and collapsed due to the massive amount of water from El Nino weather pattern induced storms eroding concrete that had cracks in it that had not been properly maintained….
My understanding was that it had nothing to do with ‘massive’ amounts of water – though those were around at the time.
It was simply that the structure had been allowed to deteriorate so badly under the assumption that water would be a thing of the past, that the dew would have started to fall through the spillway…
I’ve been involved in the pouring of probably 150,000 CY of concrete, including the structure for one NFL stadium and the foundations and turbine pedestal for a power plant. Concrete ALWAYS cracks. It is the nature of the cracks that is important. The word “hairline” would indicate minor cracking. But I would have to read the full engineer’s report to form an opinion.
Can this same excuse be given for the much smaller cracks in the containment building at Crystal River? If not why is it okay here, where failure is the immediate death of those downstream.
Well of course the spillway is cracking, and global warming is the cause. Warming temperatures cause the Earth’s crust to expand, thus causing the cracking. When will you people ever learn?
/sarc
machinists use the ‘red’ hair (politically correct version) as a unit of tininess which is @ur momisugly 0.003 inches across
Concrete always cracks. It’s a question of whether it cracks where you want it to crack (through proper design), or where it wants to crack due to expansion. That said, the proper incorporation of well designed expansion joints will prevent the appearance of “cracks”. The key there is that properly designed expansion joints can be sealed to prevent water intrusion -in most cases.
The question of rusting rebar is interesting. Rebar expands approximately eight times it’s original volume when it (completely) rusts, thus, inflicts an irresistible force on the surrounding concrete. The Romans used concrete without rebar, and much of it still stands as placed (simply making a point about the expansion of rusting rebar). I’ve also heard recent discussions of using bamboo as a replacement, since it doesn’t rust.
One thing is for certain here. Bureaucrats are masters in the art of CYA! Never underestimate their ability to sweep problems under the rug, and later make excuses for their earlier failure.
The Founders forgot to set aside one day, per year, where bureaucrats are fair game to the rest of the citizenry. Its the only way one can keep their numbers in check.
I’ll be very surprised if this is a serious problem, given the excavation to competent bedrock, the incredibly meticulous preparation of the surface to receive the concrete, the massive amount of concrete, the massive number and deep placement of anchoring rods, the massive amount of re-bar, and the very high strength structural concrete. Some of the re-bar is coated with some sort of plastic to prevent corrosion.
Typical re-bar mats: https://pixel-ca-dwr.photoshelter.com/galleries/C0000OxvlgXg3yfg/G00003YCcmDTx48Y/I0000NDqJyTwBa1s/DK-oroville-recovery-2402-06-14-2017-jpg
https://pixel-ca-dwr.photoshelter.com/galleries/C0000OxvlgXg3yfg/G00003YCcmDTx48Y/I0000iKvj0sUTZLg/KG-oroville-11113-06-16-2017-jpg
Typical corrosion resistant coating on rebar and anchor bolt placement:
https://pixel-ca-dwr.photoshelter.com/galleries/C0000OxvlgXg3yfg/G00003YCcmDTx48Y/I0000U24WnsHyDv0/KG-oroville-5418-08-02-2017-jpg
Surface prep:
https://pixel-ca-dwr.photoshelter.com/galleries/C0000OxvlgXg3yfg/G00003YCcmDTx48Y/I0000U24WnsHyDv0/KG-oroville-5418-08-02-2017-jpg
https://pixel-ca-dwr.photoshelter.com/galleries/C0000OxvlgXg3yfg/G00003YCcmDTx48Y/I0000Q335yit19A4/DK-oroville-spillway-recovery-3237-07-10-2017-jpg
https://pixel-ca-dwr.photoshelter.com/galleries/C0000OxvlgXg3yfg/G00003YCcmDTx48Y/I0000MUnbRY8b2tM/DK-oroville-spillway-recovery-2866-06-26-2017-jpg
Yes, those are men on their hands and knees with Home Depot buckets and shop vacs preparing the surface.
I’ve been following this whole Oroville dam and spillway story since its inception. I got the coverage from Juan Browne via his blancolirio channel on YouTube. His reporting has been top notch, thorough and down to earth, unlike the MSM. The new spillway is light years ahead of the old one in terms of engineering. I highly doubt “hairline cracks” would be something that was overlooked or a surprise. The concrete slabs are highly-reinforced and bolted to bedrock. There’s also many drainage areas to deal with any seepage.
It’s been an absolutely monumental task. They just recently finished with Phase One and have a full spillway again. Due to the RCC (roller-compacted concrete) section it can only handle [100K CFS (cubic feet per second)] right now, but unless the area gets another massive deluge during flood season its unlikely the spillway will even be used. The next phase is to replace the RCC section with reinforced concrete. They’ve also been working on re-engineering the emergency spillway. There’s a giant secant cutoff wall a distance away to prevent undercutting back up to the dam. Between the emergency spillway and the cutoff wall there will be an RCC pad.
California does seem to have problems doing anything correctly on the state level.
In my nuclear power career, I advocated the Frog’s Fur Standard, “fine as frog’s fur.” You do know how fine frogs fur is? So fine that it can’t be seen.
I am sure cracks are caused by elevated CO2 levels, not by utter incompetence. Concrete needs CO2 to cure properly, and if there’s too much of it, it cures fast and cracks. Just another fact of a miserable life, nothing more.
Mission accomplished, be afraid.
My understanding, as a layman, is that concrete always cracks because it shrinks as it cures. That’s why you saw pre-planned grooves in a garage floor, for example, i.e., so the cracks aren’t just randomly located.
But then there’s pre-stressed concrete which I know nothing about. Maybe that doesn’t crack and isn’t supposed to ever crack? Is that what the Berkeley expert is talking about, and is that what’s used in the new spillway? I find it hard to believe he’s just flat out wrong, given his credentials.
It was not so long ago that the advocacy cause was against all things concrete. Maybe they put too much straw in the mix or used adobe. It is California after all.
How in the heck did they manage to spend $500,000,000 on a spillway??? I know it’s California, but it seems like an outrageous amount of money.
What I find “Unbelievable” is that maybe too much acceptance is being paid to the validity of the media’s and a professor’s comments, on a site that is very skeptical of journalist and academic opinions.
I would tend to think that experienced engineers would have a better view of the realities than those other two groups.
I also have followed Juan Browne’s great coverage of the progress in the phase 1 construction of the repairs, and have been impressed with the massive scope of the project. There is still a lot of work to do.
I don’t know if these cracks are a major problem or not but I would think that a crack in a well designed structure is not as big a problem as a crack in a poorly designed structure, which I believe was the situation in the original version of the spill way. Time will tell.
Duct Tape.
🙂
Well, they probably had to pay for a new environmental impact study, climate impact study, high speed rail impact study, water district impact study, Paris Agreement impact study, gender and racial impact study, condor study, and downstream communities study. There were probably a number of theater arts productions and community meetings and surveys also. BTW this means the total cost for the CA high speed rail project is more money than the plant has in total circulation and assets.
Hmm… So it seems we have many people commenting here who have professionally poured concrete for a living who disagree with a talk-to-the-media-about-doom University Professor who says concrete never cracks. I have no skill in the matter, but I’ve seen this before somewhere.
Yeah, but just wait only Moonbeam’s bullet train is finished, it will be perfect. As with all things Californian, it will be built on time and under budget. Besides, who cares about the Oroville Dam. It won’t affect the coastal elite and the Silicon Valley mega rich.
Epoxy coating a couple of years down the road after complete curing of concrete. After application it will be too ‘slick’ to ever walk on again (unless ‘suction cup’ shoes are worn). Coating may need to be reapplied periodically every decade or so unless they build a roof over the chute to shade it.
In practical economic reality, since the spillway is seldom used, no need to worry. Just thinset grout hairline cracks and then epoxy over repairs annually as required. It’ll last a lifetime.
Hell, the human species will be extinct within 100 years according to some reports! Trying to make it last maintenance free longer than that would be like buying a 200 year contract for free hair cuts and manicures!
Sorry, but today’s concrete structures are engineered so extensively I have to laugh at the notion of hairline cracks being alarming. .
The type of concrete, steel, thickness, sizing, pattern etc as well as the anchoring to the base rock is vastly superior to what it replaced by multiples of strength and durability.
The idea of “water hurling down the spillway at 90 miles an hour” representing a serious loading is also a wildly melodramatic exaggeration.
These hairline cracks are not a weakening or paths exposing concrete to accelerated corrosion.
And this spillway will sit there unused most of the time, seldom see any flow and grow stronger with age.
The professor is actually using the language of climate alarmism.
,,,”small cracks could increase stresses when it is under “service loading”
Could? Under assumptions he doesn’t clarify.
Instead he adds elementary theoretical notions to fallaciously equate these hairline cracks to the cracks which he also suggests were responsible for the ultimate failure of the original gated spillway.
So I call BS on any worry whatsoever over these hairline cracks.
This new spillway, built with the extreme standards of 2017 is as permanent as permanent can be.
The dam itself will fail long before the new spillway does.