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.
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.
Here’s a quite higher resolution photo where you can see steel reinforcing protruding from the slabs and bent pointing downstream. It certainly looks like rebar and not welded wire mesh.
http://www.trbimg.com/img-589bea24/turbine/la-me-headlines-lake-oroville-spillway-20170207
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.
Thin concrete on the spillway, and inadequate rebar.
Any surprises in the dam wall? I’d be getting that checked.
That last picture has rebar CLEARLY VISIBLE. Some of it is even bent over the top and lying on the concrete surface.
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.
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.
“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
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.
After reading through the real expertise sprinkled throughout this thread, I must call myself out for my own idiotic comments above…D’oh!
And that self-awareness is exactly what makes you an excellent moderator Charles.
And an excellent man.
“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)…..
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.
Yes Chris, a good summation.
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.
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.
Here is a picture of the construction at Folsom Dam spillway project from last year to get an idea of the scale of rebar to expect, at least by current design standards.
http://www.sacbee.com/news/state/california/water-and-drought/jiiwvx/picture56750983/ALTERNATES/FREE_640/Folsom%20Dam02
cast in checkerboard fashon to lessen total shrinkage as the concrete cures….squares not necessarily precast tiles
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
Fill is cheaper than a suspended slab, so I doubt that a contractor would do that.
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.
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.
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.
http://forums.mtbr.com/california-norcal/ot-oroville-reservoir-situation-1034073.html
http://redirect.viglink.com/?format=go&jsonp=vglnk_148671821240913&key=6b590a383d5c8ad74c577b3652ca2031&libId=iyzlf6xs010006wf000DAb88d3zfp&loc=http%3A%2F%2Fforums.mtbr.com%2Fcalifornia-norcal%2Fot-oroville-reservoir-situation-1034073.html&v=1&out=https%3A%2F%2Fcdec.water.ca.gov%2Fcgi-progs%2FqueryF%3FORO&ref=https%3A%2F%2Fwww.google.com%2F&title=OT%3A%20The%20Oroville%20Reservoir%20situation-%20Mtbr.com&txt=https%3A%2F%2Fcdec.water.ca.gov%2Fcgi-progs%2FqueryF%3FORO
Hey Steven –
v’ v’ !
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.
An expert who considers geological features and static requirements.
Look before you leap. Or type.
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.