Looking at the many photos online of the Oroville Spillway collpase that has been in the news, there’s one major component of concrete that should be there, but is blatantly absent:
REBAR
Rebar (short for reinforcing bar), collectively known as reinforcing steel and reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and hold the concrete in tension. Rebar’s surface is often patterned to form a better bond with the concrete. Source
If there was REBAR in the spillway concrete, you’d see a mesh lattice of it left behind in the hole, or at least a few sticking out at odd angles. here are several photos, I don’t see any REBAR, do you?
ADDED: Here is a closeup view from our local newspaper, clearly no REBAR visible:
(Upon magnification of this image it appears there is some in the debris, so the question is now, was it enough, or was the problem due to some other factor)
Source: http://media.chicoer.com/2017/02/08/photos-oroville-dam-spillway-dwr/#7 (h/t to commenter TonyL)
If REBAR was present, we likely would not see such a dramatic collapse as it would have prevented water pressure cavitation from eroding more and more concrete. Concrete is a material that is very strong in compression, but relatively weak in tension. To compensate for this imbalance in concrete’s behavior, rebar is cast into it to carry the tensile loads. This means concrete pulls apart much easier than it is crushable, but with REBAR the tensile force required to pull the concrete apart is greatly increased.
One wonders if that lack of REBAR on the spillway was by design, accident, negligence, or some cost-cutting measure like the lack of life-boats and cheap steel on the Titanic. REBAR in concrete was invented in 1849. It seems incredible to me that it seems to be missing from this very important structure.
From AP:
OROVILLE, Calif. (AP) — State engineers on Thursday discovered new damage to the Oroville Dam spillway in Northern California, the tallest in the United States.
Earlier this week, chunks of concrete went flying off the emergency spillway, creating a 200-foot-long, 30-foot-deep hole.
Department of Water Resources spokesman Doug Carlson said officials will ramp up the outflow from the damaged site Thursday so officials can drain Lake Oroville.
Meanwhile, reservoir levels continued to climb behind the critical flood-control structure. Officials said it is at 90 percent of its capacity.
They said the dam is still safe and doesn’t threaten communities downstream.
“The integrity of the dam is not jeopardized in any way because the problem is with the spillway and not the dam,” said Eric See, a spokesman for the Department of Water Resources.
As a contingency, state officials are preparing to use the emergency spillway at the dam.
Crews have been clearing trees, rocks, and other debris from the hillside near the dam where water will flow.
Lake Oroville would naturally flow over this ungated concrete crest, into a mostly unlined emergency spillway if the reservoir reaches 901 feet elevation. This would be the first time the spillway has been used in the dam’s 48-year history although the reservoir came within 1 foot of flowing over in January 1997.
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At this afternoon’s press conference, Eric from DWR was asked if rebar was used, and he said it was. I don’t see any, though.
Insufficient data. Look at the people in the upper left half of the first picture. Any rebar thinner than a thigh would not be visible at this scale.
You’ve said it all. Any commentary from here on down is pointless speculation.
Oops, below I wrote #5 rebar, but that was more for standard foundation work. For slabs, welded wire mesh of certainly less than 5/8″, maybe 1/4″ – 1/2″.
see the updated photo I added
It should be visible even in the distance shots because it would be a whole multilayered formation of thick steel which would in many places be left holding chunks of concrete of various sizes, but it does bend easily and it fatigues rapidly. If the spillway got undermined enough for cracks to start flapping it could cause the rebar to break off at the cracks.
Wouldn’t happen if they had enough layers of rebar in enough depth of concrete. With one grid layer it’s easy to imagine.
I count well over 100 rebar visible in the last image. On the fer wall, it is the vertical lines that resemble a ruler. On the large chunk of concrete sitting on top there are 6 – 8 rebar sticking out as well as 4 or 5 bent over on the spillway directly above it. And 7 additional pieces bent over across the spillway at the lower right. Though without any scale reference, I can’t say if the quantity, size, or spacing is proper.
Plenty reo there … maybe incorrectly sized to hold the concrete together.
http://www.chicoer.com/general-news/20170209/spillway-crumbling-but-flows-resume-as-dwr-balances-flood-threat
New images show the split now goes from wall to wall and even has removed wall sections
Rebar is visible in some areas – and substantial rebar at that. Curiously there appears to be none of it tying the middle part of the slab to the outside walls. One would think this would be fairly integral to its structural integrity.
In addition, what is the brown layer of variable thickness beneath the slab? Sand? This would certainly allow a piping failure to occur. Whatever that layer is, below it is fairly friable and weak soil, which would also allow a piping failure.
“But rest assured, it’s not the dam, it’s only the spillway”
Ahem yes, but if that’s the standard of the spillway, what’s the standard of the dam?
If you live below this dam, you should be worried.
Bryan, that stuff on the far wall ain’t rebar. It originates from the bottom of the brown layer. Rebar would be poking out the middle of the slab and would be bent in the direction the previously attached concrete was washed away.
AP,
That would be the case unless this were the point of origin for the fault like a sink hole. The Concrete slab would Fall down into the sinkholeand bend the rebar down with it.
The Brown earthen loking area just below the wall is in fact a continuation the mountain side that is visible behind the wall and traveling down some 50′ beyond the spillway till it is underneath it in the hole. There is a substantial Air Gap between the spillway and both the ground below and beyond it
You have to be kidding me !
Somebody actually intended to run a river of water over that flimsy confarnation to empty an overfilled dam.
Those jokers with their 4 x trucks parked sideways on there must have all had a brain mummification done on them to drive their truck down there in the first place. That could have been what caused it to bend and crack.
Un-pre-stressed concrete has almost as much flexural strength as does ice.
None of these engineering hoodlums had ancestors who built the great Gothic Cathedrals of Europe did they ??
Please sir; I want to come back when the state gets a population of adults.
g
Bryan, presumably the concrete washed down hill and did not “fall” into a “sink-hole” in a direction normal to the angle of the spillway? Unless there is an intense gravity anomoly at the dam?
With Sony in Thalgau we had the exactly big bags for recycling of CD’s like ‘Counter Strike’ or
https://m.theregister.co.uk/2005/02/17/taketwo_gta_lawsuit/
geez
I see what looks like a wire mesh in the third picture. What I wold call chicken wire, certainly not a structural material.
#5 rebar is commonly used for this type of concrete slab, that’s 5/8″ diameter if I recall correctly.
That is a security fence on the curb of the raceway.
I believe the “wire mesh” is chain link fence supported by the steel posts bolted to the concrete.
I don’t see any evidence that there is rebar in any of the pictures.
# 4 bar is 1/2″ all numbering is base 8, ie; #8 bar is 1″ and #5 is 5/8″
IMO rebar is so basic that no project, much less on that has government funding therefor government inspected, would have this missing though obviously there is a failure of either construction practices or a design flaw.
As a structural engineer I concur! Often on ground bearing slabs, which this appears to be to me although details aren’t clear, concrete slabs designed to bear onto a compacted sub-strata/sub-base of some kind, we design them to span a nominal 3m (10ft) soft spot (assuming no specific loading is chosen in the design) & it often ends up requiring what is termed “minimum steel”, or As min, i.e the minimum area (A) required under a design code to control cracking, (which is what concrete does), the reinforcement is there to control that cracking! For example, an 300mm (1ft) slab, on a metre for metre grid, in the UK such minimum steel would be 0.13% of the gross cross section. We also often try to simplify things for the guys on site, by using a square/rectangular mesh fabric, as it can cut down the liklihood of errors in laying individual bars.
I posted this further down, but I feel it needs to be stated early in this thread…
There looks to be Re-Bar.. In the third image, click on it to make it full screen. Do Ctrl + several times (8 times gives you 300%, the max in FireFox) on your keyboard to zoom in on the image. On the left side of the image is the ‘peninsula’, you can see the checkerboard grid of the Re-Bar, especially on the right edge closest to the lower wall. It’s there.. It’s not high resolution, but it can be made out.
I agree. The patterning of an extensive rebar grid is clearly visible to those who know what to expect to be seen.
Also agree. An 8x expansion of picture 3 clearly shows rebar rods sticking out of the concrete.
I see it on the broken edge. Clearly it is there.
Magnify 400%, then look near the bottom left hand corner at the broken ledge.
It actually looks as if water has eroded the outside of the spillway first, and then begun to undermine it.
Note alsothe curious cracking pattern ofnear rectangulr shaping. If reinforcement was present it most likely wouldn’t crack like that!!!
I believe that the whole situation was caused by a Sink Hole type of erosion removing the earthen support from beneath the spillway along the most damaged side
Also, If you look at the top image, along the right hand side of the spillway, the external erosion is apparent and is evident some 30 – 40 feet above the top most point of failure. Further possible evidence of external erosion undermining the support and leading to the failure
No, not a “sink hole”. A piping failure.
I had to put in a cement wall about 45 feet long along my yard and a driveway next to it. The wall has to take a cement truck if ever needed. I use 1/2 inch rebar with in each foot. 8 inches thick at the top and 14 inches at the bottom. CEMENT CRACKS and there iis a few but no problems with the wall. The lot behind my land was flooding when they use their showersssssssss. NO ONE IN BUTTE COUNTY CARE AT ALL and it was #! their sewer line was CLAY, TAR and a bit of ABS but the line would plug and the clean out cap was not tight and the water would flood my yard. I dug out my land aroung my home and then put a 1 foot pipe (I.D.) down 4 feet and put into it french drains. It took me about 8 years all my hand. The county sold me the land and no one did care. I did get on the front page of the Oroville News Paper but right away a Gov. Spi Plane crash next to the NewsPaper and then I had no help from them as they move to Chico. I then got married to a woman from a diggerent country and I went to her country tooo. We cot married and she then left me with about two days when her family that are in USA came to Calif and left her parents with me for one day. Then they pack up and left me. I got was servied paper work for Court. I fill out the paper work wirth some errors so they will wave to re service me. I left my home as I move away just not the GET MAD THE THE USA SYSTEM OF LIES. It took about 10 years to find a nice acre on land and a 62 yeat old home right on the Feather River near Hwy 162 in Oroville. I have work here for 18 months on the land and the home. I had to go to different doctors for the pain my lower back, knee, elbo, and my knee. I need knee sugery, back sugery and the othes will hurt tell i find the rightt doctor then pain DRUGs. Now I am packing everything I have at my new home from the problems our syster has. I live 30 feet from the river and in the 1950s Oroville area had a FLOOd that did get 3 to 4 feet high in this home. Oroville Dam is to be a flood lake and now we have no flood control at alll. So now I can not sleep long from the Pain from MOVING picking up to much in weight, SAFE DOORS and ect…I did call the evey one about the Dam Spillway not having REBAR 1 inch thick and tighter then my wall of one foot. Our USA bridges are falling and now the spillway. I would feel better in THAILAND or Japan then in the USA for our system only LETSSSSSSSSSSSSSSSSSSSS or are BRAIN DEAD. sorry for the errors as I a, tuping in a darl room. Butte County is not to smart as look at Paradise has need a way to have sewer lines. Whey the rail road lines were taken out would been just right for the flow down Paradise waste to Chico. So with Butte County being so BUMB I know thee is a better way to live then live with their air heads as our LEADERS. So I have been to Hawaii but they have no love for teh USA Gov. TAXES and then they do not like WHITE PEOPLE but their $$$. So I went to Belize and there it was not safe but Mexico was nice. I could say more but why when out system if hurting familys that has kids that are Americans but not the Mom. So then they send the mom back to Mexico. TRUMP needs to get his ass together and out county. I hope as soon my Mom is gone I then can leave the USA to have a lot of LOVE for the land i live in. Here I have been in a Coma from a Hit and Run and other injurys from air heads and the police do ZERO or our COURTS. NASA lost alot of good people from being DUMB when they see problems but do ZERO to FIX it. No rebar in the the spillway and out lives are not safe liviing in the USA. Pack my bags amd fly to a asian country ber my dream again
errrors I so sorry
I will be looking for a lawer and hope to find other people that needs to do the same. Join together to get paid for the hell the county has been giving us. WE ARE NOT SAFE WTH OUT A FLOOD LAKE that should be at least 50 feet from the top— Bye bye to living in a county of air heads
After looking at the last window I see lots of variability that I wouldn’t expect. Along the far sidewall there is a clean break running down the spillway. If you look at the strata, you see a little bit of variable thickness, but also a distinct margin of two layers of concrete. Was the second layer added later? The thickness does not seem to be adequate given the turbulence created by the drg created between two planes. If you look you can see that the center area has concrete that is very very variable in thickness and strata. Some of it looks like the one the two layers you see above next to the wall. Some of it appears to be patches. These patches can be scene on google earth, and as I suspected, are in the affected area. It also looks like there were pockets under the concrete prior to failure you can see under the light patches.
I imagine they used the Rebar money to line their pockets with cash instead. As a retired Mine Safety Inspector the lack of Rebar and Steel Mesh was the first thing I noticed and now that they are using this breached spillway they risk Hydrodynamic Cavitation and Under Boiling thus the weakened spillway will eventually eat back into the flood gates and then it will be to late to evacuate. If I lived downstream of this ticking time bomb I’d evacuate yesterday. Ask yourself “How long can I tread Water?”. Someone at DWR needs to go to Jail and someone needs to fire all those DWR folks you see wandering about with their Hands in their pockets as now is the time for action and all those slackers are slowing down the work at hand. Those Mine Dump Truck are only hauling at half capacity, WHY? Someone at DWR is getting Rich at your expense and peril. DWR would be smart to enlist the help of some of us Retiree’s who have vast on the job experience with matters like these and not let a bunch of Text Book Jocks run the show. I’d volunteer for Free.
A lot of the breaks appear to be on construction joints, where there may be dowels but no continuous rebar (or welded wire mesh).
I do cement/rebar work in the past. It has to be laid down so it overlaps no gaps or running end to end and the overlap has to be wired together.
Quote:
This would be the first time the spillway has been used in the dam’s 48-year history although the reservoir came within 1 foot of flowing over in January 1997.
There is no rebar in the Hoover dam. I don’t know about the spillway.
wat? no rebar?
” Approximately 5 million barrels of cement and 45 million pounds of reinforcement steel had gone into what was then the tallest dam in the world, its 6.6 million tons of concrete enough to pave a road from San Francisco to New York City. Altogether, some 21,000 workers contributed to its construction.”
….well, sure–worker’s lunchboxes were noticeably heavy when their shifts were over.
Go and tour Hoover Dam and look at the construction pictures. Tons of re-bar. They poured towers away from one another so as to let the heat escape from the pour while in the curing stage. They then filled in the gaps with another tower and so on. I forgot how long it took for the entire base to cure. I think measured in years.. And to think it was completed, in what, 3 years??? Is the Bay Bridge finished yet, with all of the defects later found? 10 years plus ??
The rebar would also tie the wingwalls into the flat spillway, forming a more contiguous trough, with the walls helping to hold up the flat spillway slabs.
Hell, we even have rebar on flat stretches of concrete highway pavement, and all that does is sit on compacted soil!
Yes – reinforced concrete is used for highways. Rebar and wire mesh in the concrete supports ‘tension side’ bending loads from heavily laden trucks, improving the overall life of the concrete. The higher tensile strength steel bars and wires also act as ductile ‘fibers’ in the lower tensile strength brittle concrete matrix, creating a ‘composite’ that has better crack propagation resistance than unreinforced concrete road bed. There are many other technical benefits also.
Reinforced concrete highways are a lot more dynamic and complicated than just ‘sitting on compacted soil’.
No, not directly on soil as that would probably lead to corrosion. The rebar for flat, ground installations, is held up off the ground by “stand-off’s”, placed at regular intervals, which raise the entire mesh off of the ground allowing for concrete to be poured under and encasing the rebar.
Rebar has to be at least 2″ deep in the concrete or there’s a good chance of corrosion (rust) and eventual failure.
Yes because oxygen penetrates deep enough to cause rusting of the rebar, which swells and causes the concrete to break away from the structure and an eventual failure of the entire structure. There is a chemical test that can be performed, I can’t recall what it is, but it tests how far oxygen has penetrated and, IIRC, the indicator is a pinkish colour in the concrete.
Hy rebar is epoxy coated to prevent rust. concrete is porous to water. ” Perches” are used to keep the rebar at it’s proper place in concrete for structural reasons only.
This is the sort of thing I am talking about.
https://www.google.com.au/search?q=image+of+reinforced+concrete+posts+rust&espv=2&biw=1255&bih=621&tbm=isch&imgil=nC5qaccfxzL3aM%253A%253BkRQf4VUMwWEbmM%253Bhttp%25253A%25252F%25252Fwww.leancrew.com%25252Fall-this%25252F2014%25252F11%25252Flow-post%25252F&source=iu&pf=m&fir=nC5qaccfxzL3aM%253A%252CkRQf4VUMwWEbmM%252C_&usg=__zvXvwBqRXZFHvRk_NgZGnKQLOqw%3D&ved=0ahUKEwi4qYDOkoXSAhUCk5QKHYLIBmUQyjcIMg&ei=Yn6dWLjwNIKm0gSCkZuoBg#imgrc=nC5qaccfxzL3aM:
Before the advent of epoxy coated bars as note above.
In Mexico you can always count on the rebar being there; and in plain sight. They deliberately leave it sticking out of the roof so you can see it is still under construction.
When the rebar disappears they start taxing you on the property improvements, so you always leave the rebar showing.
G
There should have been an inspection for the rebar before the concrete was poured.
Legally, they must inspect it. I suspect bribery here.
There are lots of sleezebag contractors and they are endlessly creative. They won’t pay a bribe if they can just pull the wool over the inspector’s eyes.
If steel rebar and wire was contractually required and paid for by the state, who ended up with the money alloted for the rebar/wire? Inquiring minds need to know…
Leaving out the rebar is sadly a not uncommon way for an unscrupulous operator to raise his profit margins, especially done when that operator has gotten the work by submitting a ridiculously low bid.
I know of a large building on a well known public university where every stairwell had to be ripped out and rebuilt at huge expense because some scumbag pulled this trick. The guy who did it? He had already declared bankruptcy and disappeared the day it came to light. His company? Whoops, it no longer existed and no one knew anything about it!!! Imagine that.
Sigh. I’ll wager one and all $100 there is rebar in this spillway. Try to imagine that something this gargantuan could have been built under both California and Corp Of Engineers oversight without anyone noticing no rebar was being used. Uh … no.
The question isn’t whether rebar was used, but how it was used. Having seen a number of demolition jobs in which rebar was used, I don’t see the normal pattern of concrete blocks hanging together like that typically seen.
I suspect insufficient or poorly-placed rebar due to cost-cutting or shoddy workmanship.
Any body who has ever worked with the Corp of Engineers as I have on multiple occasions, would know that every step of the construction process is supervised by multiple inspectors whose only job is to make sure the contractor follows plans and specifications to the letter.
Now if it was a city project in NY, NJ or Chicago them perhaps. Not on a Federal job. No way, no how.
I wonder if the contractors and/or engineers who built or designed the spillway are still around. it would have recently be seriously negligent not to use continuous rebar in California, given earthquake risk, but I do not know when codes were changed.
I don’t see any rebar… but the photo resolution does not support magnification necessary for visual certainty. Looks like the water undercutting the right sidewall will create one whale of an erosion ‘gully’ on that side, should significant flow down the compromised spillway occur.
As others have said after expanding the picture and looking at the piece of concrete left about halfway down the big piece there is a chunk between the big piece and the wall that clearly shows rebar but it is hard to tell how large the pattern of the r-bar is it could be 4’x4′ that would be criminal. Almost non existent!
Rebar: you have to TIE IT TOGETHER. That is, single strands are no good. Cross tying it is time consuming I have done this more than once, I build houses.
Note how California no longer has a drought. They aren’t being roasted by ‘global warming’ which seems mostly confined to a few places like California in the recent past. Right now in NY it is 4 degrees F. Four! At 8 pm. In mid February. Wow, roasting to death here.
That is interesting… the drought ended along with the El Niño. I thought it was supposed to be the other way around, in California: El Niño = more water, La Niña = less. No?
There were some major storm systems carrying water inland during the last El Niño, but a persistent shift in the jet stream carried them North of California. What I’m not clear on is whether the strong El Niño had anything to do with driving the jet stream shift.
They’ll blame the rain on global warming now. LOL.
Correctly, at that.
GW means DRAMA. Dramatic droughts. Dramatic rainfalls. Guess what just happened one right after the other?
What’s fascinating about this is that it may have been a critical piece of what caused these failures… the clays and grouts under the dam would have been dried out and dessicated after the drought conditions… if the water came back up too fast (which it did) it could penetrate some of these seals with legit pressures that could cause piping before they were able to swell back into shape by being rehydrated.
Some of the inspectors are looking at this as a particular fail mode right now.
Actually, the Titantic was scheduled to have twice as many lifeboats installed as soon as it returned from its maiden voyage to New York. I also don’t believe people still question the steel, but they have questioned the strength of the rivets. They also could have saved quite a few more passengers if the lifeboats had been filled, and if they could have launched lifeboats on the side highest due to the list – the Titantic was designated to be one of His Royal Majesty’s troop carriers in time of war and was built very tall, not the best design for a ship trying to launch lifeboats.
Titanic was originally designed to carry sufficient lifeboats, even though at the time there was no law requiring to fit them. The number of boats and bulkhead changes were made to fit the boat with more luxury, the grand stairwell for instance. With regards to the steel used, it was of poor quality, with lots of impurities, and became brittle at very cold temperatures. The rivets, originally specified, were replaced with cheaper, lower grade, items as the company was running out of money before going in to building and under extreme pressure to complete the ship on time and under budget.
A recent documentary I saw showed correspondence which alluded to a lesser grade of steel being used, to save costs…
In a Materials course we were taught the Ductile-Brittle Transion Temperate was not well understood until investigated after early WWII Liberty Ships kept splitting in half while transversing the North Atlantic.
“Griff February 10, 2017 at 4:51 am”
No the steel plates were “top of the line” at the time. What “crippled” that quality was the rivets, which IIFC, were wrought iron, not steel. Basically “unzipped” when the hull struck the iceberg.
There is also a new theory, There may have been a slow burning coal fire in one of the holds that weakened the steel and so was more easily torn by the iceberg. I am still waiting for many more “Theories”
Another theory is that if the captain simply reversed the engines and rammed the iceberg, causing damage at the bow similar to a sister ship, only one or two compartments would have flooded and would not have sunk.
Patrick, that’s not just a theory.
What doomed the Titanic was water flooding into the first 5 compartments. This pulled the bow down enough so that water was able to flow over the top of the containment wall on the 5th compartment, into the 6th, which pulled the bow down ever further, which allowed even more water to overflow and so on.
A frontal collision would have caused water to enter the first compartment, and structural damage may have allowed that water to leak into the second compartment.
Two compartments flooded, the Titanic stays afloat.
PS, it’s likely that the leakage into the second compartment would have been slow enough that the pumps could have kept it under control.
As to life boats, at the time, life boats were not designed to hold all of the passengers. Rather they were intended to ferry passengers from the sinking ship to a rescue vessel.
Had the California not shut it’s radio down, it’s possible that it could have arrived in time to rescue most of the passengers.
Had they not lost the binoculars used by the lookouts, it’s possible they would have spotted the iceberg in time to avoid it.
I once asked a specialist in marine safety what he thought about the Titanic. His answer was:
“Here you have a ship that is driven at more than 20 knots through a known iceberg area. When an iceberg is sighted it is steered in a way that maximizes the damage from the collision. Even after that it stays afloat and on an even keel for five hours and power remains on throughout, giving ample time to radio for help and to evacuate passengers and crew. I call that a safe ship.”
The collision happened during the night shift; the captain was in his quarters.
When the berg was spotted, a full reverse on the engines was called and the crew at the wheel made a hard turn to starboard. A nautical equivalent of both braking and swerving a car in response to an imminent head-on collision. Doing both together was a panic-induced mistake; turn sensitivity increases at higher speeds and decreases at lower speeds, whether at land or sea. A hard turn at speed would likely have cleared the berg. Alternatively, reversing engines and maintaining course would have hit the berg head on, breaching less of the hull. Instead, they did the worst of both worlds, crippling the ship’s maneuverability and exposing the most possible hull area to a breach.
As an aside, only the main propeller on the ship was designed to reverse gear. The auxiliary propellers on each side would have continued to turn in their original directions from momentum, slowing down the slowing down, so to speak.
“MarkW February 10, 2017 at 6:34 am”
Yes I know. The 6th(+) bulkhead(s) was(were) lowered for “luxury fittings” such as the stairwell. The top of the 6th bulkhead was only about 2m above the water line.
“drednicolson February 11, 2017 at 2:05 pm”
Yes, anyone who has driven on snow/ice will know. You add some interesting points.
Popular Mechanics (Yes, of all places) had an excellent article years ago that took actual pieces of the steel from the Titanic and found it was very brittle. Apparently, the steel was relatively new in composition but they didn’t test it thoroughly. Oops.
You would assume the engineers followed standard design practices, but the spillway did fail, didn’t it?
I think that they have used rebar. Have a look at the LHS of the hole, where the break is internal to the concrete panels. There are extremely jagged edges. Elswhere, entire panels have been washed out, so we have no idea what the internal structure of them was.
Two words: Cypress Structure.
There was rebar in the Cypress Street freeway, just not enough and in the wrong configuration.
Looking at the bottom photo, if there had been rebar and/or mesh used, the Queensland shaped piece would have numerous chunks of concrete hanging off, tied into the remaining piece. By the look of the damage, it is just poured concrete, and there is nothing to tie it together.
The technical term for this special type of profit-making “reo” is “slip-mesh” : laid for ‘inspection’, then slipped out for later re-use, and re-use, and re-use. Many faulty masonry fences and pathways testify to its popularity.
Here’s the authority for CA dams – Division of Safety of Dams (DSOD):
http://www.water.ca.gov/damsafety/
Relicensing here, with environmental issues:
http://www.water.ca.gov/orovillerelicensing/
Its all OK! And safe! If the spillway washes out enough the dam cannot possibly fail! Right!! The Titanic can’t sink and the Hindenburg cannot burn!
I have experience with rebar versus no-rebar. It makes all the difference and never lay concrete without rebar. Just don’t.
Poured a 6″ concrete drive way, 80 feet long, 20 ft. wide. I used a friend who is a Commercial Concrete contractor here in California, and he said that concrete with rebar always cracks, due to difference in modulus elasticity (What I believe he said). Expansion joints are necessary to alleviate the cracks, but they do not always prevent cracks. .. Vertical structures are perfect for re-bar, with large horizontal structures having the most problems. (Their own weight starts the failure). So, he suggested 6″ of highway base, heavily compacted ,(By the 10 yard concrete truck that was doing the “hardrock, 3/4″ gravel pour, not a 1/4 ” pump pour) , and he used Fibermesh concrete. A fiberglass type material is blended into the concrete at the plant. Granted, this is not a “structural ” slab, per se, but in 5 years of 110 degree summers and 23 degree winters, droughts and deluges and being used by our local garbage trucks (the big ones), we have only 3 spider cracks, all from the sides of sharp sidewalk entries, where no expansion joints were used. Different strokes, I guess..
At the time the Cypress Structure was built by the gubment, rebar was not required by whatever building codes applied to gubment projects. If the Oroville damn was built under the same codes, we may have a teensy bit of a problem.
https://en.wikipedia.org/wiki/Cypress_Street_Viaduct
However, you can see lots of rebar squirting out of the support columns on the Cypress Viaduct.
The Cypress Structure was also built of a sequence of identical modules; for economies of mass construction. So each freeway section between uprights had the same frequency of oscillation.
And the Cypress Structure just happened to point almost directly towards Loma Prieta where the epi center was so the longitudinal earthquake surface wave was just a head on drive of a nice resonant structure. If the sections had been made a range of different length between uprights they would have all fought against each other instead of being in unison.
It was a collapse waiting to happen.
And it happened as soon as it could happen.
G
That’ll buff out. There must be an engineering society keeping its head down right about now.
You must have a reason for saying that, Mike. May I ask what it is?
There is a ancient Roman recipe for concrete which doesn’t use rebar, the modern version is used today.
The difference is how the concrete is applied. The concrete is applied very dry, and pounded into position – in Roman times slaves with hammers, nowadays with industrial vibrating impactors.
The hammering removes voids, making the concrete far stronger than normal.
Obviously if you mess up the application process, you end up with mush.
https://en.wikipedia.org/wiki/Roman_concrete
Thanks Eric, that is interesting , gee maybe I should have listened to my dad!. As an aside I used
“Fibrecrete” in some projects, a mixture of concrete and glass fibre. very useful when having curves and nonlinear structures I used landscaping.
There are still many old ‘caverns’ under Rome, where the hardened volcanic ash was extracted to make concrete… occasionally buildings collapse into them.
If you go to the tomb of Caecilia Metella along the Appian Way, you can see remnants of one such excavation..
The great wall of China used 3% sticky rice in the mortar between the bricks. It’s a lot stronger than ordinary cement.
G
Does man-made CO2 weaken concrete…?
All of our concrete is going to die!
Yes, and cement plants are huge CO2 emitters! Planet-destroying emitters, in fact!
Do cement plants absorb CO2 like other kinds of plants?
I would like to conduct a study to see how “carbon” dissolves rebar in concrete structures. I’ll have to use federal grant money, of course. I think I’ll start with $8 million and go from there.
“Do cement plants absorb CO2 like other kinds of plants?”
OMG! I never realized this obvious thingie! The cement plant emits CO2 but then absorbs it back again, so it’s net-neutral! #Science!
There looks to be Re-Bar.. In the third image, click on it to make it full screen. Do Ctrl + several times on your keyboard to zoom in on the image. On the left side of the image is the ‘peninsula’, you can see the checkerboard grid of the Re-Bar, especially on the right edge closest to the lower wall. It’s there.. It’s not high resolution, but it can be made out.
I was about to recommend sending for the men in white coats when I clearly saw the checkerboard, right by the jog on the downhill end of the exposed slab. That’s not wiremesh. There’s nobody / nothing nearby to give the scale, but it looks just like you say, rebar. Well spotted, Mike.
You must be one of those few people who can see the gunman on the grassy knoll too 😉
Looks more like a geotechnical failure. Earth and rock fill dams of this scale require all aquifers in the vicinity of the dam wall and spillway structures to be grouted to block the movement of water under or adjacent to them. If you fail in this, subsoil erosion will occur and create what are sometimes called sink holes. The dam operators would normally have installed inspection wells along with seismographic equipment to monitor soil moisture and earth movement and therefore should have detected this failure before it caused the damage it did. Such failures may take some time to occur (about 50 years in this case) but they are inevitable if you haven’t done your homework. If I was a Californian I would now be worried about the dam wall itself. What else was missed in the geotechnical analysis that was carried out prior to construction? The issue of reinforcing bars is misleading. The quantity of steel added would have been adequate for control of cracking and minor expansion or contraction movement, but the design would have been developed on the basis the structure was fully supported on its subgrade. Take away the subgrade and it won’t last very long.
Good points.
Lindsay – Yup – probably an erosion problem – to be safe, better look for more…
Regards, Allan M. Eng. (Geotech.)
I’d keep an eye out for the Fly Ash Liberation as well.
Fly Ash Liberation Army that is, the dread FLA.
Right now the Tennessee Valley Authority is repairing Boone Dam because the earthen portion of the structure, built on karst, has been undermined by seepage from the reservoir. The re-grouting process is in its second year with as much as five more years to go. Boone Dam was built in the early 1950’s. What type of bedrock was Oroville built on?
We recently had these issues addressed in Lake Lewisville, which is upstream to Dallas, Texas.
Over the years inspection wells and inspection ‘walks’ have regularly been performed in order to keep abreast of any changes in the structure and surrounding soil. We had record rains in 2014 which pushed water levels in all our reservoirs up emphasizing the need for repairs when deficiency were noted.
“The Army Corps of Engineers will need millions of dollars to repair the Lewisville Lake Dam, one of the nation’s most dangerous. A breach could put 431,000 people in harm’s way.”
http://interactives.dallasnews.com/2015/lewisville-dam/
“High-risk Lewisville Lake dam gets Congressional funding for important safety improvements”
http://www.dallasnews.com/news/news/2016/04/06/high-risk-lewisville-lake-dam-gets-congressional-funding-for-safety-improvements
I would be very worried if I lived down stream. One article said, and I paraphrase, “don’t worry the dam has not actually failed”. Clearly the photograph shows the classic Mohr Circle slip failure that occurs in fully saturated soils with low cohesion, ie clay soils. This is a failure in materials selection and compaction during construction. The fact the dam has not yet been breached is misleading. It clearly will. It just needs a bit more time and rain. The dam has already failed. The safest repair is straight forward in that a coffer dam needs to be constructed to isolate the failure, dewater, remove and rebuild the entire dam wall section giving careful attention to materials selection and compaction. The real danger of a breach in an earth and rock fill dam is that once a breach occurs it rapidly enlarges and results in catastrophic colapse of the dam wall. Murphy’s Law says this will be in the middle of night when it is bucketing down making evacuation problematic. When you assess the risks, the main costs will be in loss of life followed by loss of water supply, infrastructure and housing. The cost of properly repairing the dam structure is minor by comparison given the potential scale of these losses. I am truly surprised at how these articles pretty well brushed over the potential for catastrophic loss. You are however fortunate that the failure has been identified in time.
Nah, it’s just as safe as the Mullholand dam.
+1
My old boss was the engineer who designed this dam. I’m sure he designed this properly. He was a very good structural engineer. This would have a state project and inspections would be required by the engineering firm. Theses are slabs on grade and there are obvious expansion joints in the concrete. You can see where the slabs have failed along these joints. Although it is true that reinforcing is required for tensile stresses in the concrete, for unloaded slabs on grade there would be negligible steel required for bending stresses. The reinforcing used would only be for temperature and shrinkage stresses. Very light so they probably used welded wire fabric. On some of the slabs not broken at the expansion joints there is no reinforcing visible. However when slab break off like this using WWF the reinforcing will also break at the Crack. With a photo at this scale I doubt it would be visible.
The reinforcing is not continuous through the expansion joint. Doing this would defeat the purpose of an expansion joint.
The failure in the slave is obvious due to the undermining of the slab. This was most likely due to poor maintenance.
Interesting post.
How are inspections performed for on the slap to check for undermining – could this be checked by a visual inspection during a simple walk, or would a scuba diver be needed?