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.
The “skeptic” is a denier.
This crack is “normal and expected” here, and I predict it will be the best.
Can’t believe I am the first to say it … CO2 made it crack clearly.
Was thinking more along the lines of a global warming buckle.
But just think of all the jobs created by fixing all the cracks!!!
“Professor Robert Bea, a veteran analyst of structure failures, said cracking in high-strength reinforced concrete structures is never expected.”
…but since it’s in California…
If the cracks are expected and nothing to worry about then why the hell were those cracks not designed into the spillway design to begin with ??
That way they would be able to say the structure is exactly as we designed it to be.
It sounds like a repeat of the San Francisco-Oakland Bay Bridge fiasco, where the bridge had already started to self destruct before it was even open to the public for regular use.
Count me as one person who will never drive nor set foot on that disaster waiting to happen.
The Oroville Dam spillway is just asking for trouble. Why don’t they get some more heavy trucks to go out on that structure to inspect the cracks, and cause the structural failure like they did 12 or so years ago. That gaping hole is right where those trucks used to be parked. You wouldn’t get me to even walk out on that structure to inspect cracks, let alone drive a heavy truck down there.
Their so-called reinforced concrete looks like it is molded around chicken wire.
You can’t bend concrete; even with chicken wire inside it. That just ensures that when the concrete finally breaks it will stay attached to the chicken wire, instead of all falling on the ground.
If they can’t use a pre-stressed concrete design then they need to support the slab with pilings that go down to the bed rock, instead of having it float above a bed of mine tailings piled up until it rains.
G
George, look at the photos and videos in my post below, and explore the others available at CA-DWR’s Pixel account and YouTube account. You will see very clearly that the new spillway construction is a dam sight stronger than you are thinking.
i foresee a hundred thousand dollars of epoxy in oroville’s future
Rusting rebar is a big deal in parking structures located in northern climes where salt is used to de-ice the roads. As such, it is well understood.
There are many techniques to prevent rust if the structure is already completed and develops cracks. link That said, the best thing is just to build it right in the first place.
hairline cracks is too subjective a term for me.
get any slab wet and it will show you a zillion ‘hairline cracks’ on the surface
panic for its own sake doesn’t thrill me like it does the lovers of gothic doom that always squeal for attention…
While attending Cal Poly Pomona, I worked in the auto shop. My boss had a sign over his desk:
Why is there never enough time to do something right the 1st time and always enough time to do it over?
the definition of concrete is, “it’s gray and it cracks” even a Post Tension slab will develop cracks.
A slab of any substantial size will have cracks.
Maybe they should have used Roman concrete
I wonder if this was a lowest bid contract. Or a crony contractor. Or….. well, you get the idea.
Well they need to put 3% of sticky rice into the concrete to hold it together. Much stronger than modern cement.
That’s what has held the great walls of China together for eons.
G
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.
” Concrete ALWAYS cracks”
This is what I’ve always thought. My question is, “How is it possible that concrete won’t crack”?
Agree with you Wright. Concrete cracks period. It is the intensity, depth and quantity of cracks that needs to be evaluated.
garywgrubbs
Hence the development of self-healing concrete. That would seem to be the perfect material for California: Heal thyself before telling others how to heal themselves. In California there is nothing quite like a concrete idea to reinforce confidence.
Crispin in Waterloo but really in Toronto
Ouch. Dad joke alert.
🙂
Cracks that allow water to reach the rebar, immediately or over time are no acceptable
I used to work in construction a couple off decades ago and the massive foundation slaps we lowered in by crane had NO cracks of any depth, and cracked slabs were DISPOSED of if the cracks were more than a couple of inches deep (in slabs that were 8 feet depth)
Water gets in cracks, and when winter comes around, the freeze expands the cracks
So, in this case, even minor cracks will grow every year
Also concrete “hairline” cracks are not the same as bone hairline cracks, they are bigger. “hairline” is misleading
No picking at IChingbeam’s foresight, Crispin. Or his concrete czar. Keep it civil.
I too was involved in a lot of concrete pours , working for a structural engineering company. Engineers wanted the mix as dry as possible (3-4 inch slump) an still be workable–the workers on the pour wanted it as wet as the truck could make it saw some that would be in the 10-12 inch slump range. The “hairline” cracking is due to shrinkage during curing, the wetter the pour, the more evident cracking will show up. Could certainly become an issue where water is intended to run over the surface–depending on the amount and width of the initial “hairline cracking”, but is not the same as structural cracks caused by poor base compaction, or soil heave potential that was not engineered for.
Exactly … keep in mind these concrete pours were also on a slope …. there were multiple lifts of reinforced concrete, of varying types. We are talking many FEET of concrete at minimum – and dozens of feet in a good chunk of the structure.
I have never seen concrete that has not developed cracks – no matter the type of pour.
3-4” slump w/ or w/out superplasticizer?
B
Yep…there’s a lot of “depending” regarding this one….would be nice to see some photos with something for comparison. What some people call a “hairline crack” goes much deeper. I’ve seen some repairs on a barely visible crack turn out to be 1/4″ deep or more – and much wider than a “hair”.
… and small cracks are self-healing. For particular values of ‘small’.
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.
Collapse of the spillway merely means that erosion of that hillside will be greater.
There is a solid rock ridge between the spillway and the dam itself.
Failure of the spillway cannot endanger the dam.
The dam is just piled up dirt; not concrete, and that includes on the downstream side where the spillway is. There is no solid rock under the spillway. Who cares what is between it and the dam; it is supported by nothing.
G
CR3’s untimely end was a pity. It came about by the local utility thinking “other plants have done Steam Generator replacements successfully using experienced contract engineering and construction firms, so we should be able to handle it by ourselves.” After they messed up their containment structure, the estimate to fix it was about what it would cost to build a new plant. Not worth it. Too bad – I had given them a new lease on life in 1990, when I figured out why they had been cracking reactor coolant pump shafts throughout the 1980s (they had 6 such events – no other B&W reactor had such issues). The RCP cracks were also self-inflicted – all due to a well-intentioned design change to their shaft seal (too long a story for the comments, but a fun one to explain under the right circumstances).
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
Precisely.
The BBC today had an article about Julius Ceasar’s invasion of Britain. I had to remind them that as this occurred during The Roman Warm Period, maybe we should start expecting some other similarly terrible events as a result of global warming.
michael hart
See!….See!!
Global warming induced migration!
Damn! The greenies were right all along!
Ahem.
machinists use the ‘red’ hair (politically correct version) as a unit of tininess which is @ 0.003 inches across
+1000
I have only ever heard the politically incorrect version, something tells me you made the “red” part up.
at uni there was one woman in the industrial technology lab course, so that was what was taught.
Is this related to King Cnute?
My father invented a unit if distance that was invoked when reading slide rules (quite a necessity when trying to get a third or occasionally fourth significant digit) called the “cunth”. An answer to a calculation might be: “6.82 and 3 cunths”. The physical distance (like 0.003″) was not applicable as it can be used for a logarithmic scale being simply an interpolation made with a well-tuned eye. Any skilled user of a slide rule will be familiar with this unit even if they did not know its actual name.
Crispin in Waterloo but really in Toronto
Is a cunth something like a ‘that’ll f”kn do?’
I believe the “cunth” unit of measure is widespread. I have heard it expressed when measuring and cutting in close tolerances as a “cunth’ heavy or a “cunth” light. As accurately marking is subject to some error, after after marking the error is reduced by cutting with the “cunth” factor.
Is anyone else vaguely disturbed by this word? I feel like, for some reason, I shouldn’t use it around kids or something…
🙂
rip
Can’t say as I’d recommend the word around vagins, either.
But it’s useful if you’re not cock sure
You must mean the RCH, indeed a small dimension.
You mean RCH, I assume.
During my Navy tour, 1960-64, in Electronic Technician school, I was taught that, “5 plus or minus 1 rch”, with the 5 being some arbitrary value.
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.
I was always a proponent of fiber reinforced concrete. Why couldn’t fiberglass (don’t need graphite) cordage be pre-stressed (stretched) during cure to cause compression in the slab similar to how rebar is used on pre-stressed concrete.
Absolutely no corrosion there.
RS,
Actually, glass does corrode. Look at old glass in museums. It typically has a surface patina of many colors caused by light interference between the de-vitrified surface and the interior. Since it tends to happen at the surface, it will proceed more rapidly with a large surface area, such as with glass fibers. It is also accelerated by the presence of water. I imagine that a chemical reaction will take place between the proposed glass fiber and the cement in the presence of water, elevated temperatures, and high pH.
The photographs of the new replacement slab rebars are colored light green, which means that they are coated with epoxy and will resist rusting. Yes, unprotected rebar will rust and expand and will degrade the concrete.
Do you agree that hairline cracks in concrete self-heal in the sense that concrete continues to absorb CO2 for a long time after it is cast? Concrete continues to harden for at least a century. Doesn’t this tend to fill small gaps by increasing the volume of the material?
Crispin, you are correct. I’ve seen that effect under the microscope where very fine cracks have been infilled with CaCO3. In general carbonation results in a decrease in porosity and an increase in strength with time. This does not necessarily happen with coarser cracks though as optimum moisture conditions are required – not too wet, not too dry.
The Roman engineers never put concrete in tensile loading. They couldn’t. Concrete in compression is of course very strong, it is when it is put in tension that a reinforcing bar/matrix that has tensile strength is mandatory.
Romans thus became expert at building arches as a result where all the loading is compression. The Roman structures that we see still standing today are those that have survived the natural selection of being properly constructed with the materials of that era.
On Roroville:
The steep slope of the Oroville spillway means there is always going to be a strong tendency to downhill sub-base slippage, which then pulls downward on the concrete spillway. So if I were looking at the Oroville spillway plans, I’d be looking at what was under the spillway structure and how to stop subbase slippage. No amount of rebar and spillway slab thickening will work if the sub-base is slipping downslope.
Deep driven Pilings? Cassions? to bedrock or Epoxy injection to the fill sub-base?
The Oroville spillway was cleaned out to stable bedrock and then concrete was extensively anchored to the bedrock.
It appeared to me that the original was not, and that was #1 on the failure reason list.
Given your observation, there should be no problems with the spillway … cracks or no (did you see the work?).
Gerry Parker
I tried to remove half a dozen brick from a buried Victorian well I found in my garden, to allow a soil pipe to run properly.
Those half a dozen bricks broke 2 Kango hammers. Not concrete, I admit, but somehow, despite all our technology, cement and concrete don’t seem to be as good as they used to be.
My grandfather poured his shop/garage slab himself (about 30′ x 36′). No expansion/contraction joints, poured on dirt, with reinforcement of leftover chainsaw chains. That was more than 80 years ago (I didn’t see it go in) and there are no visible cracks anywhere.
Saw a 100 year old single car garage slab (10′ x 20′) removed. Thickness varied from 5″ to 10″; reinforcement was tin cans, chains & whatever metal they had laying around. Again, no visible cracks. It wanted to come out in one piece … had to work to break it so excavator could pick it up.
The best response I get when asking why is “probably very low slump”. Learn how to work it and pour it dry.
Basalt rebar is coming in wider use, as is basalt fibers. With the use of steel rebar, however, keeping water out is a real solution. Particle-packed mixes using engineered gradations of pozzolans and mineral additives such as granite dust, fly ash, metakaolin, silica fume, make for concretes virtually impervious to water intrusion. Add micro or nano-fibers and crystalline waterproofers and even cracks up to 4/10 mm are self-healed, preventing the development of larger cracks.
Don Perry,
Thank you for the information about basalt rebar. I didn’t know that such material existed. Very interesting!
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.
How many years did it take for the first one to fail, my guess is most of the politician will be living off their ridiculous pensions when this one fails.
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.
Excellent sources! Thanks for posting. The “some sort of plastic” is an epoxy coating used to resist corrosion. In my professional engineering opinion, all slab rebar for this project should be epoxy coated.
David J. Bufalo
Forgive my ignorance, but if it’s such a critical component, in a vital infrastructure, why not use stainless steel reinforcement?
I would opine that stainless steel would be too expensive.
I followed the repair project closely, and echo what others have said about the excellent coverage from Juan Brown.
CA-DWR published at least a couple of videos per week to YouTube showing the progress of the work. These are beautifully done. The composition, editing, music, are all just outstanding. If there were an Oscar category for construction videos, these would win in a clean sweep.
They’re available here:
This one, in particular, is a work of art, IMHO.
David J. Bufalo
“I would opine that stainless steel would be too expensive.”
That was my first thought, but then on such a politically sensitive project one might think the extra cost would be inconsequential, especially considering the final cost.
@David J;
Stainless steels have lower yield stress limits than standard steels. Also, absent a plastic coating, they are more subject to chloride stress cracks than standard steels. Rebar can be 60-80 kip/in² while 304/316 stainless is 25-30 kip/in².
D.J. Thank you so very much for that information. I appreciate it.
“excavation to competent bedrock,”
Yes, serpentine rock is very strong as long as it does not come into contact with oxygen, in which case it weathers very quickly, It was this that caused the extreme erosion of the emergency spillway and made it necessary to use the damaged main spillway. I do hope that they have carefully sealed off that competent bedrock, because otherwse it won’t stay competent for long.
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.
Make that 100K CFS, not 100. Really need to be able to edit posts.
Try “proof reading” before hitting post comment. It really works.
I did and do. It’s easy to overlook a simple missing letter vs a bigger mistake. The fact that we still can’t edit posts even when the capability is available is ridiculous.
Preview would be better.
deebodk
You issued a correction following your mis post.
Isn’t that more conversant with scientific and engineering conventions than editing?
You might guess, I’m neither a scientist nor an engineer.
I needed a secretary. I noticed a note in the liquor shop, ‘free alcohol’. No damn it was ‘alcohol free’ after all.
Editing of comments is coming soon
Yay!
deebodk: Thank you for noting this. I also have been following this from the beginning with Juan Browne and was about to post it. His commentary and presentations are top notch, informative, and without the bias seen elsewhere. The engineering on that project was well done with very careful quality control evidenced by the production facility at the site. It appears that the engineering is addressing some of the basic flaws in the original design including RCC fill down to bedrock in the plunge pools created by the failure. Phase 1 was intended to get the spillway operational to some level with phase 2 providing full upgrade. I, like many here, am skeptical of the political “tradeoffs” California made leading up to the failure. It would appear that this project is working to do the rebuild correctly this time. I would recommend those skeptical (like me) take a look at what Juan Browne has to say. Here is a link to the complete set of videos on the failure and its reconstruction,
I have aslo been following, from the UK, Juan Browne’s excellent coverage of the ongoing Oroville saga, ever since I read about the problems with the spillway reported by WUWT, back in February.
It was a salutary lesson to witness the sheer power of Nature as it destroyed man’s best efforts at taming it.
Juan, and his ‘Mighty Luscombe’, have shown just how effective one person can be reporting on, and explaining in easily understandable terms, this major engineering project.
Juan sets an example with his personal integrity and enthusiasm that many others in the media would do well to emulate.
I’ve been following Juan Browne’s blancolirio channel as well. Agree his reporting is top notch.
Thanks for putting up this comment. I’ve followed Juan Browne’s videos and I think the work looks good. I’m looking forward to his response to this news.
California does seem to have problems doing anything correctly on the state level.
You have to understand that within the California State Government, Jerry Brown is the only adult in the room. Explains it all.
Even ‘Uncle Jerry’ needs adult supervision. Good luck with that.
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.
Also, because of the elevated temperatures (because CO2), the concrete cures too quickly.
And many commercial concrete mixes have catalysts added to accelerate curing.
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.
The grooves are more for allowing thermal expansion, I think.
There are different reasons.
One is that if you cut a nice line then you see a nice line (not the crack underneath). Crack it on purpose every 10 feet or so…. Also acts as contraction joint.
Expansion joints are another thing altogether.
They are called control joints i.e. to control where the cracks occur. Not always successfully.
Mixes can also be engineered to counteract the tendency of Portland mixes to shrink by adding a quantity of cement that is expansive when it cures. The biggest problem is in convincing those in charge that there are new methods that are superior to “the way it’s always been done”.
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.
You mean Calizuela.
Here is everything you need to know about concrete…
Concrete is a profoundly horrible structural material. It’s ugly, rather inconsistent and unpredictable, it has no tensile strength, it shrinks, creeps, cracks and more.
It has one redeeming quality: it’s really, really, cheap!
One more concrete characteristic: Pour a large slab right up next to your house and it’s almost guaranteed to eventually tip toward the house creating a serious drainage issue in many cases. But, as you said, it’s cheap.
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.
Organic concrete is hard to find, especially the non-GMO variety.
good one RG
Could it be federal taxpayer money?
And how much would they have to spend to rebuild every city down stream of the dam? (Including Sacratomato)
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.
It’s more that we have been trained by experience to expect incompetence whenever the government is involved.
For the government of California, that goes double.
Indeed, Juan’s coverage of the whole Oroville Dam situation has been by far the best. If you want no-nonsense, no hype info on what’s happening at Oroville, check out his “blancolirio” channel on YouTube.
Duct Tape.
🙂
Shoe Goo™
J B Weld
Chewing gum
Water-expanding gorilla glue. Lots of it.
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.
He is a professor at the University of California, Berkeley.
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.
According to yesterday;s news report, the High Speed Train to Nowhere is now projected to be grossly over budget and grossly behind schedule. But that’s OK – it’ll be way cool when it is finished.
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.
When I moved to California, I noticed that they just add a layer of black paint (and white stripes) to asphalt parking lots instead of repaving them. It covers up the ugly dirt that accumulates for lack of rain and those ‘minor’ cracks. Some places seem to need a dose every year.
Maybe the magic paint comes in white for concrete?
Professor Bea may be out of his Emeritus, but the State of California denied for decades that there was a problem. They deserve the skepticism that they are receiving.
Cure cracks, The more water used the bigger they are.
As a structural engineer, I find the professor’s comments very odd. Concrete has to crack in order for the reinforcing bars to provide resistance. (no strain, no force) Ideally, these cracks are very fine and not noticeable. In a large slab, cracks will occur due to the concrete shrinking during curing. This volume change effect is very difficult to eliminate (there are special additives and post-tension techniques, but these are not cure-alls), so we provide joints to provide strain relief. Essentially, joints are straight cracks that we caulk.
The reinforcing in the pictures is epoxy-coated – the same technique is used in concrete bridges. There can be issues with the coating chipping – but if installed properly, the rebar will last for a very long time. In the spillway condition, I would expect the bars to essentially last forever – because in order to corrode you need water and an electrolyte. In bridges, the electrolyte is the deicing salt. I would not imagine they would deice the spillway very often. Concrete has corrosion inhibition properties until the electrolyte (typically chloride ion) loading reaches a critical point.
One issue with cracks in concrete is water infiltration that freezes – freeze-thaw. As ice expands, it can spall the surface of the concrete over many cycles. Modern mix designs incorporate air entertainment of closed cell bubbles that allow a bit of “spring” inside the concrete – this allows the concrete to accept the strain from the ice without as much damage. Combined with higher strength mix designs, these concretes are very durable. I do not have the specifics on the concrete mix they are using but this standard practice for exposed concrete.
Yes, you can provide a coating to waterproof the surface. But you will have to maintain it; most coatings need replacement in under 10 years due to UV degradation. However, by using epoxy rebar, modern concrete mix designs for durability and minimizing cracks, that should not be necessary for long term durability.
[Although less well known than entrainment, air entertainment is much springier… -mod]
UC Berkely Professor Robert Brea earned his Ph.D. is from the Center for Oil & Gas Engineering at the University of Western Australia. The UC Berkely website states his 48 years of expertise is in “engineering and management of design, construction, maintenance, operation, and decommissioning marine systems including offshore platforms, pipelines, and floating facilities.”
This guy is not an expert on concrete structures…
Did you mean Bea instead of Brea or is there a Brea at Berkely?
You are correct…
Maybe they could’ve had Mark Jacobson put in ten times more turbines.
“Unbelievable”
No, it’s not. It’s the Dem stronghold of Caliphornia.
It seems that “robust” is a very popular word these days.
As an principal engineer I can tell you small cracks on high strength concrete is not uncommon – many standards even allow for it! That professor probably hasnt ever worked in the real world. Hair line cracks typically self heal and are not an issue. Concrete shrinks as it cures so small cracks can form especially when working on a exposed site during hot fine weather. However its hard to comment in detail not being familiar with the concrete used specifically. For a spillway you would expect something very durable due to flow velocity and abrasion i.e. super plasticised wire reinforced at a.strength greater than 70mpa. A bigger issue is a tomo forming underneath causing the slab to span a void it wasnt designed to span as happened on the last one!
Despite extolling the design and construction of the repairs, I have to say the slagging of Dr. Bea is unwarranted. He is a very serious guy with very serious credentials. His particular specialty is failure analysis, and he’s one of the top guys in the US in that area, and has been hired to analyze many engineering disaster events. He runs a program at U.C. Berkeley on this topic. His reports on the Oroville Dam are thorough and well-reasoned and well-documented. He might be wrong about some things, but one thing he is not is incompetent.
Second, the issue of the cracks wasn’t raised by a bunch of cranks or trolls. It was the Federal Energy Regulatory Commission, also very serious people.
This structure was cast in hundreds of pours..for the cast portion. Thousands of lifts for roller compacted concrete. Yes, there WILL be curing cracks as I didn’t see any post tension process where steel reinforcement is tensioned after initial cure to put the concrete into compressed state. Post tension is the only way to prevent cure cracking in a structure of this size.
Now, will cure cracks doom this spillway? Not in the areas replaced to bedrock. In other areas ? Aerators and turbulators can be added if cracks will experience cavitation in areas without prep to bedrock.
The original spillway survived many prior uses of equal magnitude. It was lack of PM which led to failure. Most likely, plugged drains which allowed water pressure to lift slabs after reinforcement failure from corrosion.
we know concrete cracks, but as long as they are not builders cracks I think they will be fine.
Like others, I’ve watched this saga closely on a daily basis since the original spillway collapsed. Before people light their hair on fire, let’s wait for the final report. If the cracks are merely due to shrinkage, it’s very different than if the cracks were caused by settling. I will be very surprised if the cracks turn out to be problematic. The structural concrete is laid on a very well-prepared layer of leveling concrete, which is laid on prepared rock. The structural layer is thick and has extensive rebar. This is very different from the original concrete, which was thin, had insufficient rebar and was laid on badly weathered rock.
Correct me if wrong, but I thought the original spillway was undermined.
$500 million for a 900 m spillway ? seriously? 1/2 f***ing million per meter ? for a thing that should be used once per century, or so ?
paqyfelyc
The alternative is loss of the dam during any subsequent period of high snowfall and rains, and complete loss of every town and city down river from the dam between the mountains and the north San Francisco Bay and estuary region. Tens of billions of dollars in damages and tens of thousands of lives. Worse, the loss one year could be repeated each subsequent year. Loss of power, loss of the irrigation and drinking water storage. Loss of the farmland.
The Original spillway was poorly constructed and failed. The high water and high snowfall that over-flowed the spillway, causing the first small cracks and erosion damage that caused the catastrophic/unstoppable damage last spring threaten the dam integrity and utility itself.
Permit me to doubt that 1/2 billion dollar are required for this job done. And, BTW, a perfectly flat surface is just plainly stupid if you want to stand a huge water flow. 1000 m3/s falling 10 m are mgh/s = 98 10^6 W, that’s why water can destroy piers and cliffs. It should be irregular and cascading, to use air and vortex to slow water, turn higher energy water into mist, and introduce bubbles, so as prevent energy to build up in the flow into destructive waves. Piers are done of irregular blocks for a reason. Actually two reasons. 1) it is cheap, much more so than a wall. And 2) the very same reason natural rapids are so irregular: because a flat surface is destroyed and broken apart, where an irregular stands.
As Bob Kelly once told me, “There are two kinds of concrete. Concrete that is cracked and concrete that is gonna crack.”
For the best reporter on Oroville:
Juan Brown —