Oroville Dam Spillway collapse may be due to missing REBAR

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?

oroville-dam-damage

oroville-dam-spillway

kg_oro_spillway_damage_9974

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)

oroville-spillway-closeup-chicoer

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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246 thoughts on “Oroville Dam Spillway collapse may be due to missing REBAR

  1. 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.

      • 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″.

      • 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.

      • 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?

    • 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.

      • 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.

      • 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

    • 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

      • 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.

  2. 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.

  3. 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.”

      • 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 ??

  4. 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!

      • 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.

  5. 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.

  6. 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!

  7. 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.

  8. 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.

      • 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.

      • 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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!

    • 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..

    • 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

  14. That’ll buff out. There must be an engineering society keeping its head down right about now.

  15. 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.

    • 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!

  16. 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.

  17. 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.

    • 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.

  18. 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?

    • Tony L, pretty amazing pictures in the gallery. Pictures show the failure in progress; water got in underneath the slab and washed out the fill rather than primarily cavitation breaking up the concrete.

    • TonyL February 9, 2017 at 6:07 pm

      Good evening Tony and all.
      Thanks for the photo group. First I am not a engineer. Now to those who are look at things other then the hole. First in #10 look at the over flow entries on ether side of the barrier wall note the water flow. Of course at the failed area their is none. Now look at 11#, see the retaining wall just above the failed area at 90-70 degrees from the spillway? If the spillway was never used did the side wall run-off holes become blocked and that area erode away? If water backed up under that area did it manage to rust the supports rebar?

      Someone is going to have there hands full on this. Thankfully no one hurt and and chance for all to learn.

      Michael

      • I’m sorry, you have to have a Ph.D in geotechnical engineering to have an opinion on this. They have sophisticated computer modelling that proves the cause of it and no, you can’t see how it works. it’s proprietary and you might find something wrong with it.

      • PiperPaul February 9, 2017 at 8:12 pm
        before I retired, it this point I would simple toss someone bringing such news into a CNC chip conveyor (juicing them) now I can only pout.

        michael

  19. 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.

    “The steel used for the Titanic was far inferior to the steel typically used today, and was much more brittle and not nearly as impact resistant. However, it was certainly the best steel that could be produced at the time. Leighly concluded that flaws in the design of the ship were a much bigger factor of the sinking of the Titanic than the actual steel used in production.” – from http://www.capitalsteel.net/news/blog/steel-titanic

  20. An alternative to rebar or mesh could be the tying-in of adjoining slabs with starter bars; short lengths of rebar cast into the slabs.
    It also looks like the spillway concrete was cast on natural ground.
    If the spillway was designed only to prevent erosion, high compressive strength concrete of, say, 40Mpa should provide sufficient abrasion resistance. base failure is another matter.

    • It appears that the break coincides with the trail approaching the right side of the spillway. There appears to be water upstream of the break also along the right side of the spillway.

  21. I’m pretty sure this is precast construction… so a lot of huge prefab tiles that are just lifted into place, from the bottom up. Reobar would be in each tile section but would not tie each section together. Rebates are cast into the section edges to lock it all together. ( as can be seen along the sides ) As stated… a geothechnical problem has caused the tiles to be undermined.

    • This obvious not precast….you wouldn’t use precast for a slab on grade. The tiles are individual poured sections with expansion joints between them.

      A Geotechnical problems did not cause the problem….it is highly likely that poor maintenance on the expansion joints ( failure in the sealant) allowed water to enter beneath
      And to undermine the slabs.

      • Looks like the case. Check out TonyL’s pictures above. In the gallery there are pictures of the failure in progress.

  22. More reinforcement or not it wouldn’t have mattered. Concrete on a 25% slope, with no ground support underneath is going to fall down. And with 20,000 cfs of flow through the hole, the failed concrete it is going to be carried away. The spillway wasn’t intended to bridge anything and when the (poor) subgrade finally disappeared, through long term(?) erosion, nothing was going to stop the collapse.

    See videos of high flows across the failure … it held up surprisingly well. And where it is supported by native rock it survived completely. No structure anywhere is designed to withstand the hydraulic forces encountered after the collapse.

    Also note the last photo above (left side-middle); The water uplift broke and pushed that slab up, where it remained because of the reinforcement. Opposite that slab are a couple of irregular pieces that are hanging on by the reinforcement.

    Maybe the rebar lap could have been greater (or tied better?), but it wasn’t being designed as span decking or for uplift forces.

    Somebody blew it originally by not removing and replacing the area the eroded away & somebody else blew it by not noticing that the material erosion was running down the hill (my guess is that the erosion started as soon as the project was complete).

    The annual inspection is more enjoyable when it is sunny. When it is raining (which is when they could have seen that they were losing material and that the east wall footing base was acting as a sub drain) inspection is less enjoyable.

    Just ignore it for now and fix it in the summer. This way they won’t have to demo as much prior to reconstruct. During reconstruct run a “beam” under the spillway every 50 feet … not for support but to intercept subflows and direct to weephole in side walls, and as deadman.

  23. Not all concrete structures need rebar. Hoover dam has miles of cooling pipes but not rebar. All compression? I am pretty sure the spillways and diversion tunnels, which have three ft of concrete lining, also have no rebar.

  24. Can’t even pour a driveway without a rebar inspection in most counties, and the rebar requirements in any state approved spillway plans would have been massive. Don’t know how such a glaring omission could have escaped notice.

  25. It looks ugly but it isn’t a safety issue. The hill on which that spillway sits is not part of the dam proper. There is no reason to put rebar in there as there is no requirement for structural strength. The concrete is just a path for water to flow on and rebar will not save the pavement once the earth underneath is eroded away as you can see in many street collapses. This looks like water got under the structure on the right side (as looking up from the bottom) and undermined it. It will leave a scar but it isn’t going to hurt anything. Rebar would simply add unnecessary cost.

    • Concrete cracks as it shrinks, Crosspatch, that’s often why rebar is used tocontrol that cracking! ;-)

  26. Like in any other field, e.g. climate science, it helps if you know what you’re talking about.
    In this case a bunch of people with no knowledge of structural engineering somehow think they know better, sounds familiar ?.

    • And there YOU are again with your vile name. “WTH” would get the job done and not be as disgustingly vile. But, then, it wouldn’t be an apt nickname for YOU, would it.

      • Janice

        Falls from high horses can be dangerous.

        WTF is a very acceptable and direct from of communication. When communicating on a marine radio it should followed by ‘over’.

        WTFO

      • I guess that’s why you just muck around in the mud at their feet. Glad you enjoy it so much. To each his or her own.

  27. Lindsay is correct – it is a geotechnical issue brought about by the failure to keep water from undermining the spillway proper. The dip and strike of the rock units point to a potential problem. This is exacerbated by the weathering profile of the various rock units. From the photographs, clay is forming above a slate. The clay is stable if kept dry but notoriously unstable if there is water ingress as appears to have happened here.

  28. Eerily similar to the erosion of the Glenn Canyon Dam spillways in 1983. Those were clearly reinforced. According to current engineering notions water should never be able get at the concrete enough to even make reinforcement relevant. Surely the “weight” stress increase is minimal during a storm.

    It must be a pothole effect, or like washboarding in a road. A pattern of cavitation once started developing enormous persistance and force.

    In the case of Glenn Canyon they could feel and later see chuncks of concrete, and later the rock laterally supporting the dam, bouncing down the spillways and ejecting.

  29. This smacks of perhaps a construction decision because of cost overruns or design incompetence. The way Northern California is getting creamed by successive intense rain systems this can’t end well if there are two or three more of these super soak-er systems and the citizens of Oroville might want re-evaluate where they are living. It doesn’t look to me like they can lower lake level fast enough of the rains don’t soon stop.

  30. There was some patching repair in 2013 just below where this large initial failure occurred. A picture of this 2013 patching depicted several pickup trucks inside of the spillway, one parked next to the the left hand wall. The failure at 35,000 cu ft/sec was during a gradual increase up to the maximum gate capacity of 100,000 cu ft/sec. The gates were closed and engineers many made some sort of analysis. There was movement of heavy equipment, along with truck loads of rip rap staged somewhere nearby, a road was being constructed into the failure site. Today the gates were reopened, to 70,000 cu ft/sec as the dam/lake was at 880 ft crest is 900 ft. None of the rip rap was untilized. There are many pictures showing the initial failure and the gradual increase in collapse. One viewpoint from DWR was a sink hole type of erosion caused the first collapse of surface concrete. The now ongoing release at 70,000 has eroded the right hand outside of spillway natural terrain creating an every growing width and depth trench. The sidewalls of the spillway are massive, my estimate of 16-20 ft tall. One picture phase of this initial failure showed one sidewall suspended for about 150 ft estimated from the DWR claim that the failure was 220 feet long. In the lower edge of the initial failure the slab concrete is on solid rock. Pictures during the engineering analysis the sub surface up slope is deeply eroded with a significant hollowed out cave like undermining. Approximately per-second 4,200,000 pounds moving down hill.

  31. crosspatch has it right. “It looks ugly but it isn’t a safety issue.” One should add ‘not at this time’, as long as the heavy rains stop.

    As to Rob Bradley’s comment, this is a great example of differentiating between a weather event and a climate event. Weather events can be catastrophic in the short term. Climate events happen over much longer periods.

  32. There is an access road on the right side (looking up-slope) that looks like water would run down that road and against the side. The washout begins there.
    Shows best in the photos of the ChicoER link.

  33. And while some of us look forward to a wonderful future of high tech, information technology, mini cameras and silica fibres supplying and controlling our every need, desire and essential service – some of us are waiting for the day humans can successfully get 2 friggin rocks to remain sitting on top of one another.

    Yet we are *so* convinced we are *so* clever

  34. This guy, likely nuts about the explosives, but the erosion could rapidly grow and work back towards the leading edge of the earthen dam and then it’s over.

    http://82.221.129.208/baasepagew2.html
    ” The Oroville dam is going to overflow and there is nothing they can do to stop it.
    Right now the inflow is 180,000 cfs and they can only get rid of at most 30,000 cfs. The conditions at the dam were greatly worsened by increased rains. I still believe the spillway was destroyed with explosives to prevent a controlled release. If the spillway was not damaged, it would handle the current inflow without incident. However, now they are going to have to let the water flow over the mountain that forms part of the dam, and that has never been done before. If the mountain cannot take the beating, it is going to be GAME OVER.
    At the current inflow rates, once the dam overtops the mountain will have to take, at this time, the full fury of the entire Niagra falls, TIMES TWO, and worse, Niagra falls only has a drop of a little more than 200 feet. This water will do a drop of 900 feet. It is going to be epic, even if it does not end up being an epic disaster.

    There is nothing they can do to stop this, because with the spillway as damaged as it is, there will be little difference between letting the dam overflow and trying to use the spillway which is effectively destroyed.

    The silence of the government is deafening. They are still telling the public not to worry. I believe that is negligent to the point of criminal. At the current rate of rising water, the dam will overtop tomorrow. If you live downstream it would be a very good idea to pack the car and take a week end vacation.”

  35. DC, won’t be a safety issue even if the entire hill washes away, will cost more to repair, though.

  36. If you guys question the Oroville Dam engineering, you ought to see the job CALTRANS did on the replacement Bay Bridge between Oakland and San Francisco.

  37. The rebar is clearly visible in picture #4 sticking out of the chunk of concrete sitting on top of the main collapsed spillway, as well as from the collapsed spillway and bent over the surface from the force of the water (right next to that block sitting on top of it). I think the bigger question is whether there’s an issue with the spacing of the rebar. It’s difficult to gauge size based on a photo with no references; it’s possible that with an increased spacing the tensile strength was compromised, much like spacing wall studs at 22″ or 24″ on center will not be sufficient for snow loads compared to that of studs centered on 16″.

    We’ll learn more in days to come, but clearly there’s rebar present, and at only 125% resolution.

    • I initially thought that the rebar was bent by upstream portions of collapsed slab sliding over top of still-intact portions. Doubt if water pressure would be enough to bend the rebar.

  38. Thin concrete on the spillway, and inadequate rebar.
    Any surprises in the dam wall? I’d be getting that checked.

  39. That last picture has rebar CLEARLY VISIBLE. Some of it is even bent over the top and lying on the concrete surface.

  40. what this article has to do with global warming/climate change?
    =======================
    Rain will be a thing of the past in California. Little children will grow up wondering what rain looks like.

    Wasn’t global warming supposed to bring drought to California? Apparently the weather didn’t get the memo. Because, after all, weather isn’t climate. So while the weather makes it wetter, the climate makes it drier, all at the same time and place. The more it rains, the drier it gets.

    • Alarmists (such as Bill Nye) just said last year that California was now in permanent drought.

      I’d say this qualifies as topical.

      The drought of 1975-77 was worse than the past few years and the precipitation of 2010/11 was also greater (so far) than this season. This is actually just part of normal California.

  41. There is abundant rebar in the last photograph, and given the scale of the photo it would have to be at least 5/8″ to 1″ in diameter in order to be visible at all. Look carefully and you will see it throughout the debris. In many places it is still holding slabs of concrete more-or-less together. In others, stubs up to several feet long are protruding from slab edges, often folded back over the slab from being torn free during the collapse.

  42. “some cost-cutting measure like the lack of life-boats and cheap steel on the Titanic”

    Well… just a little bit of correction added here (check these facts if you like).

    The designers/engineers/builders of the Titanic followed the “current building codes” that government/industry bureaucrats decided where “adequate” when allocating lifeboats to the ship.

    As I understand it, the calculations of “number of lifeboats required” was based on “Ship Displacement” rather than “Number of Souls On Board”. So the ships designers followed the “expert” knowledge and followed what the ‘consensus” knowledge indicated was the appropriate (at that time) Precautionary Principle.

    The designers and builders of the Titanic did not (In my opinion) try to save money by scrimping on lifeboats. They believed they where following the consensus science and never envisioned the loss of the ship so quickly that no other vessel could arrive and assist in the safe evacuation of passengers.

    It sailed will all the “currently understood” safety features that “scientists” determined where necessary,

    Regarding “cheep steel”, I suspect that very few followers of WUWT have ever even attempted to make steel (a very messy and uncomfortable process). Very convenient of folks with a century of hard earned knowledge about making steel behind them (learned by folks that actually did it) to state that others over a century ago used “cheap steel”…..

    For f…s sake, give the designers of the Titanic a break, but for a very unfortunate sequence of events that ship could have sailed back and forth across the Atlantic Ocean for decades without any problems.

    All of the other ships sailing back and forth across the Atlantic “way back then” where equipped more poorly than the Titanic. If any of the other ships in the North Atlantic that night hit an iceberg without a wireless radio they would have simply “disappeared” without any trace and it would have been an “Act of God”.

    If the Gubermint of Ca can’t specify, build and certify a simple concrete dam it is most certainly not a time to denigrate the designers/builder/operators of the Titanic, or the poor souls that perished.

    Cheers, KevinK

  43. Time will tell on the rebar but take it from someone who lives about an hour south in the Sierra foothills, the rain has been relentless since early Jan.

    To my untrained eyes, the failure may be due to massive rainwater runoff on the SIDE of the spillway structure undermining the earth that the spillway rests on, causing collapse.

    On the news tonight one of the experts said that the erosion on that area would slow way down as it was now almost down to bedrock.
    They also said the inflow from the tributaries at the rear of the lake were over four times the outflow of the functioning spillway today.

    The videos since Tuesday have been spectacular. Hope no one gets hurt by this.

  44. “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”

    Interesting question to the army corpse of engineers!

    • I would not call the rebar visible sufficient-it lacks the continuity needed ie no mesh or long rods. The erosion from under one side may,or may not, have exposed a scam. It is California after all. Ask any Texan and they’ll tell you (this from my old West Texan Skipper Bob O’Farrell, though Cali’s have a different slant)…..

  45. Portland cement slabs on grade can be designed either with or without rebar. It is a matter of base conditions and load. The base is part of the design of the slab. The sidewalls would have had rebar, and one is spanning the opening as a beam. Rebar is not the issue.

    The failure is due to water getting under the slab and eroding the base. The question is how the water got there. It could be through an expansion joint (as Jamie suggested) or from along the sidewalls. It will take investigation.

    The structure is over 50 years old, that’s a significant portion of the expected life of such a structure, so construction or design quality is not likely to be an issue. These things do occasionally need repair.

    Since the area is underlain with rock, total failure is not likely, though it’s going to look ugly.

    • I have to add that buoyancy is also a possibility. The ground is saturated as shown by the copious amount of water coming from the weepholes in the sides. This would produce a buoyant (lifting) force on the bottom of the slab. A portion of the slab would lift, allow flowing water underneath, and the failure would progress from there.

      That would have been fought in design with more weep holes or more weight of the slab, make the slab thicker. Another not rebar.

  46. One wonders if that lack of REBAR on the spillway was by design, accident, negligence, or some cost-cutting measure

    One also wonders if the designers of the spillway called for any rebar in it.

  47. cast in checkerboard fashon to lessen total shrinkage as the concrete cures….squares not necessarily precast tiles

  48. Hi Chris 4692 – note that only about a third of the slab is founded on rock – the remainder appears to have been on a clay lens.

    Is that the remains of wooden shuttering under the edge of the slab? Was there a hollow in the ground level and the contractor chose to build a suspended slab over it rather than import and compact fill?

    If so then the placement of the rebar in the slab becomes an issue. I see varying depths of placement.

    With the slipway running near to capacity the suspended slab could very well begin to vibrate – eventually lifting enough for the water to peel one section loose and exposing the clay below to erosion.

    What I can’t quite figure out is what removed a section of the fencing on top of the one side wall. Too localised.

    cheers edi

    • Was there a hollow in the ground level and the contractor chose to build a suspended slab over it rather than import and compact fill?

      Fill is cheaper than a suspended slab, so I doubt that a contractor would do that.

  49. If you enlarge the added photo the rebar is clearly visible.

    See the section in the centre that points like an isthmus up the slipway, you can clearly see rebar folded back flat in the opposite direction, the direction of flow.

  50. The water speed in this spillway is tearing on concrete. If air is added in the layer between concrete and water the wear will be reduced.

  51. If someone gives a spillway in order then he does not take the cheapest offer but pais an expert who assesses the supplier’s blueprints and assesses the finished structure. If the customer saves the expert’s costs, the customer is to blame. The customer got what he paid for.

    • And the newspapers could have brought the photos anytime since there were interesting photos to take.

      They did not during Obama legislation but in times of Trump legislation.

      Everybody may draw his own conclusions.

  52. The whole thing is grossly dangerous – think of children playing! It should have been renovated long ago!
    Is there any access lock at all. If so, what is their state.

  53. After reviewing the photos in the following link
    http://media.chicoer.com/2017/02/08/photos-oroville-dam-spillway-dwr/#3

    here’s a possible failure scenario (without having visited the site, this is pretty much conjecture on my part).

    It appears that the ditch lining failed adjacent to the spillway, probably due to heavy storm water runoff from adjacent terrain (photos 2, 3 and 4 of 13).

    Given how steep the spillway and adjacent ditch are (about 530′ drop in 3080′ or about 17 per cent – rough measurement using Google Earth), the water velocity in the ditch was very high and if the rainfall run-off from the adjacent terrain was high enough, the ditch capacity could have been exceeded, with water overflowing the lined ditch and washing out soil adjacent to the ditch, leading to the ditch lining itself being undermined and failing.

    Once the ditch lining failed, the backfill under the spillway was washed out and the spillway was undermined leaving a large void under the spillway,

    The spillway appears to be 175′ wide on Google Earth. The spillway was designed as a slab on grade (requiring a lot less reinforcing steel) and was not designed to act as a bridge when not supported by embankment.

    The spillway sidewall (vertical wall of spillway) appears to be acting as a beam, bridging the washout (photos 6, 7 and 11 of 13). This is probably the next point of failure, as the span over the washout increases.

    The spillway is probably ok about 100′ above failure point where you start to see the ditch lining failure and exposed embankment (photo 3 of 11). The spillway still needs to be cored its entire length (probably every 50 to 100 feet longitudinally and with cores at the center and 70′ each side) to check for voids under the spillway.

    The areas of primary concern (photo 12 of 13) are on the right side where the soil is exposed (light brown) below the failure and the protective ditch lining has washed away.

    Hard to tell from the photos, but it looks like there are two layers of concrete. The lower level was probably a layer of unreinforced concrete or soil cement (soil mixed with cement) called a seal slab to provide a working surface for the structural (reinforced) concrete of the spillway floor.

  54. Absolutely off topic re “Global Warming” – but I did not start the discussion:

    In some concrete reciepes, rebar is replaced by stainless steel fibres, typically 50 mm long and 1 mm diameter. Moderately popular for parking lots etc.

    Steel quality in shipbuilding: the introduction of arc welding necessiated new steel composition – riveted ships could accept entirely different steels. More Liberty ships sunk due to metallurgical failures than number sunk by German warfare.

  55. For an actual case of a government project where some rebar was missing, look up the Montreal Olympic stadium which had some large chunks fall to the ground. It was built for the 1976 summer games. Quebec contractors are still well known for corruption and organized crime connections. Back then the politicians were indistinguishable from the crime bosses.

  56. I would guess that no amount of REBAR would have prevented this, because AFAIK the problem here appears to be that water got underneath the concrete and washed out the soil between the concrete and the bedrock. I’d guess this was a process going on over a longer time.

  57. What did the Bid Request say? Did it specify rebar and at what standard?

    When we lived in Minnesota there was a big highway project to replace a ton of bridges. The problem was that the bid request did not specify salt resistant concrete in a snowbound state. The bridges were all built with standard concrete and just a few years later that all had to be rebuilt. More than double the money.

  58. Living in FL, we frequently see shots of sink holes! This looks like a typical sink hole caused by water flow UNDER the spillway. Possibly an undetected underground spring that has increased volume due to all the rain CA has gotten this year. Or it might be caused by a leak in the dam below the spillway entrance! If this is the cause, rebar wouldn’t have stopped this collapse.

  59. The sidewalls and the narrow inner skirt may be connected by rebar, as they are still intact, but because they are still intact, one cannot prove this. However, the sidewall/inner skirt combination does not seem to have interconnecting rebar to the “driveway” part of the spillway. Note the dark brown vertical lines going into the soil next to the edge of the skirt – very regular, man-made. No re-bar extending outward from the edge of the inner skirt into the failed “driveway” part of the spillway. Seems odd to me.

  60. Oops.

    “[Un]suitable for the general assembly of the public”

    60 Million (US) high school stadium in Tejas exhibits serious cracking in concrete structure

    THIS was in 2014 !!

    • Thank you, blank Jim! That was a treat to watch. Good to see one of California’s good governors there at the end, too. :)

      Engineers are the BEST!

      #(:))

  61. Mosher above – Great links to nice photos.

    It looks like cracks may have been visible in 2013.

    Also interesting is that there appear to be PGE transmission towers crossing the emergency spillway.

    • re: “Also interesting is that there appear to be PGE transmission towers crossing the emergency spillway.”

      Cold this somehow in any way (even remotely!) be connected with the power generating station located at the Oroville dam?

  62. 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.

    *****************************************
    so theres an emergency spillway.
    and its not maintained in a manner that allows its emergency use.
    small wonder the main spillway failed…

    • The “emergency spillway” aka “the doomsday dam” is not an actual spillway. Its the designed hardened low spot in the dam where (in extremis) the water is supposed to overflow to prevent damage to the main part of this earth filled dam.

    • The spillway of Canyon Lake TX was also designed this way so during the 500 year flood 2002 eroded the spillway which blocked the river preventing operation of the floodgates. The erosion made an interesting feature about two miles long which is now a protected park.

  63. Seems pretty clear that the substrate supporting the spillway was removed.
    Next questions might be when, and more importantly how.
    Lots of engineers sweating right about now.

  64. Lack of control joints caused concrete to crack. Reinforcement corroded. Saturated soil under cracks and venturi effect sucked fines up through cracks when the spillway was flowing. Foundation was undermined and caused surface failure.

  65. It looks like Mosher is looking to bone up on some other fields than Climate services…;>)

    Next up – Nick!

    T-Man

  66. There is some rebar visible in the fifth picture in the piece of concrete lying on the big one. But the concrete is mucht too thin for this kind of construction. Also the points of breakage look strange. Like the concrete was poorly mixed, not enough of cement, not enough compaction, too dry, too cold, whatever.

  67. Also, there’s the problem of ‘Durchstanzen’ (punching shear?).
    If a supporting pillar is too thin or not enough rebar installed, the concrete and the rebar may shear off. Then probably no rebar would be visible. This happened to a parking lot in Switzerland a few years ago. They built the lot, put about a metre of soil on top for a playground/park. All went well, until a car burnt out in the parking lot and the rebar melted.

  68. iRill, in the fifth image you see the chain link fence in front. If you zoom in, you can clearly see some wirelike bent things coming out of the concrete. If the concrete is 10 inch thick, then those rebar wires would be maybe 1/4 inch, which is much too thin for this load.

  69. No one has mentioned the most probable cause. This spillway was poured using concrete. This was done in sections or slabs. This means that between each section or slab , there would be expansion joints (as you would have on a freeway or patio) In this case, these gaps would be filled with a caulking compound which is able to stretch and compress with the expansion and contraction of the concrete floor. If honest inspections are done,I am certain they will find that there was a gap in the slabs which allowed water to rush underneath and undermine the soil supporting the underside of this chute. Once a cavity was washed away; the concrete was required to do what it was not designed to do ( with or without rebar) It had to span a large distance without support underneath and with tons of water to hold up.
    I suspect the experts know this and will remain silent about it as it would indicate a lack of simple maintenance. The before images show area’s of patching, etc , but this could have been avoided. I.M.O.

  70. Look at the water spraying out of the side walls in some of the photos. It appears that there is water pressure (several feet of head) UNDER to slab due to the fact that the earth on the side graded to go away from the wall. It looks like the original failure was erosion from water underneath the slab. The water that is high enough on the sides to come out of those high weep holes would erode the supporting earth under the slab and lead to failures. The fact that the walls stayed up for some time longer than the slab indicates that there is much more steel in the walls and the first few feet of slab adjacent to the walls but very little or no steel in the slab. Once the soil is eroded from under the slab the slab fails. The “Repair” will have to be replacement of the whole slab or a new layer of reinforced concretes on top of the slab.

  71. CORRECTION: Look at the water spraying out of the side walls in some of the photos. It appears that there is water pressure (several feet of head) UNDER to slab due to the fact that the earth on the side IS NOT graded to drain water away from the wall. It looks like the original failure was erosion from water underneath the slab. The water that is high enough on the sides to come out of those high weep holes would also erode the supporting earth under the slab and lead to failures. The fact that the walls stayed up for some time longer than the slab indicates that there is much more steel in the walls and the first few feet of slab adjacent to the walls but very little or no steel in the slab. Once the soil is eroded from under the slab the slab fails. The “Repair” will have to be replacement of the whole slab or a new layer of reinforced concrete on top of the slab.

  72. In my opinion the spillway would be better if is was cleaned out down to the bedrock, rebar installed and tied on top of elevation blocks to to elevate it from the bed rock and a minimum of 3′ of concrete for the water bed surface. It is hard to believe that the engineers built this spillway without reinforcing steel bars with such a shallow pour of concrete. The smallest crack would start undermining the surface with the force created by the water as it cascades down the spillway. Ballast should also be placed about half way up the side rails and about up to 8′ outboard to support and stabilize the structure.

    • my driveway has steel mesh in it and seems to about as thick as the spillway the amount of money they spend on this stuff is jaw dropping they could have built a one time use state of the art steel plant on site just so they could have lined the spill way with stainless steel and still been under budget on has to ask were does the money go its not in labor or the supplies not much of that was used maybe it all went downstream with the water funny but on top of tax dollars being spent to build these things they also collect from what people pay to have running water

  73. As a civil engineer that was my first observation “where is the reinforcing steel? It should be sticking out of the remaining concrete. It dies not appear to be there….

  74. What a terribly misinformed garbage article by a sensationalist. All this does is attract droves of armchair structural engineers and construction experts, none of whom actually have been on the site in question, let alone had their hands on the contract documents and drawings.

    There is reinforcement in the primary spillway in question, noticeably visible in a number of photographs. Whether it was enough to mitigate some of the damage that resulted, or was even intended for such a precautionary purpose in the first place, the author clearly doesn’t know. But he forges ahead in spite of this ignorance. It’s just irresponsible.

    And, no, I’m not at all defending those who were involved in the design of the Oroville Dam and its related components. Clearly, some things have occurred that were either poorly predicted or unsatisfactorily addressed prior to February 2017.

    I guess I’m just calling out the author for his clear attempt to stir the pot in the first place, his success in doing so (evidenced by roughly 150 subsequent replies, mine included) notwithstanding.

    REPLY to PHIL LANTON: Mr. Lanton, our local news media was asking the same questions that I was. The question was legitimate, and via this thread and added photographs, we answered the question, as did our local news media. If you don’t like it, that’s fine. You are entitled to your opinion. I’m also entitled to my opinin, and my opinion is that your accusation of “stirring the pot” is way off base.

    I put this thread together only AFTER I had contacted my local newspaper and local TV station news editors (I know both) and vetted the issue with them. I asked readers what they saw, I asked readers for help in identifying the issue, and I passed that info on to our local TV station and newspaper, where they were satisfied, as I was.

    You call me a “sensationalist”, without knowing one thing about why this story was in place. I call you some some armchair quarterback from North Carolina with nothing more than a long distance opinion, who’s never been on the dam as I have, never interacted with the news media, and only knew about it because some other news outlet “sensationalized” it enough for it to reach you. – Anthony Watts

    • Another armchair observation. One presumes that piping under the spillway was analyzed and dealt with in the design. Is it possible that this flow under the spillway did take place and the pressure from this piping manesfted itself at the point under the spillway where the concrete blew out? There was an earthquake in the location after the filling of the reservoir which could have created fisures in the underlying rock, through which the piping could have occurred unbeknownst to anyone and defying detection by inspections.

  75. Most likely, we will hear from a team of engineers that investigate this spillway failure. I suspect that severe undermining of the spillway foundation material had been occurring for many years resulting in a void(s) that enlarged to such an extent that the rebar could not support that span once it became loaded by the full engagement of the spillway.

    The rebar is intended to keep the slabs from cracking and is also used to pin the slabs together and to the vertical side walls. Any cracks that may have developed due to undermining would lead to an acceleration of the undermining due to the high velocity jets of water scouring out the foundation materials. As the compromised slab(s) deflect and move, projecting edges occur which are then impacted by the extremely high velocity discharges. It all results in a cascading failure.

    Unlike a prestressed concrete beam, the slab steel is not intended to support the loaded concrete slab over large voids.

    Design of dams has changed over the years. This dam was constructed in 1968. It appears from the clos-up photos that the side walls were independently constructed with a heel and a toe, much like a retaining wall. It’s hard to tell without being there on the ground, but it appears that the slabs were then dowelled into the toe of the side walls, as there is a uniform construction joint along that section of the failure.

    The spillway was reportedly in need of maintenance, repair or rehabilitation per previous accounts. A FOIA request of the State’s Dam Safety Inspections would provide that information. I spent 15 years with a state dam safety program and 18 years in the private sector analyzing, designing and repairing new and existing dams. The forensics team will be thorough and may take some time to determine the cause of the chute failure.

    However, we may see an accelerated design and repair project due to the critical nature of the dam and the reservoir for both flood prevention; and more importantly, for its water supply.

    Extremely interesting project failure. I wish I was on the forensics/design team.

  76. I found some video that will prove to be very instrumental in determining the cause of the failure. Note at the very start of the video where the gates have been closed on the principal spillway (concrete spillway); there is an enormous amount of water exiting the weep holes from the side walls.

    Weep holes should not be gushing water like a fire hydrant. Those weep holes are located above (upstream) of the failed slab section. That tells me that there was undermining from massive seepage flows. I would suspect that a very large section of the remaining slab has been undermined to various degrees and may need to be replaced.

    Typically the weep holes are the outlets for a drainage system behind the side walls. Normally, one would also design an underdrain that collects and discharges any seepage that may occur under the slabs.

    I noted this very early on in the video presentations of the event; however, no mention has been made of whether this high flow seepage condition from the weep holes had been observed in previous inspections of the dam when the lake level was high.

    Understanding that the lake had been low for several years (at about 40% capacity); the recent rains and snow melt has resulted in a maximum reservoir level that may not have occurred in a long while or perhaps ever in the life of the dam. There may not have been any recent observations of this seepage condition.

    It also occurs to me that discharges over the ogee-crest emergency spillway may have directed flows to one side wall. However, the video shows extremely high weep hole flows from both sides of the principal spillway

    Damn, I would sure love to see previous state dam safety reports. They would be fairly enlightening. If you do FOIA them, be sure to ask for earlier inspections when the lake level was high. You can check historical lake levels and tailor your request for those dates or just after.

  77. GTA – grand theft auto.

    All that’s left from the ‘american dream’.

    chocking all over my spill board.

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