Oroville Dam Spillway Failure

[sweepleader]

I thought 'rip rap' meant like dumping gravel then concreting like they did on the emergency spillway. maybe someone could write the company and ask them how they filled the voids.

The BOC refers to this concrete over rock as cyclopean backfill on page three of their memo:

"cyclopean backfill placed downstream of the approximately 1,000-ft-long monolithic ogee weir section."

https://www.metabunk.org/oroville-dam-spillway-failure.t8381/page-38#post-203671

Which does not really jive with the definition from Wiki that describes Cyclopean as "Cyclopean masonry is a type of stonework found in Mycenaean architecture, built with massive limestone boulders, roughly fitted together with minimal clearance between adjacent stones and no use of mortar."

https://en.wikipedia.org/wiki/Cyclopean_masonry

So I assume the term is used in dam construction circles and all those guys know what they mean. Rip rap is pretty commonly used as above in Aaron Z's post.

 

[EricL]

I thought 'rip rap' meant like dumping gravel then concreting like they did on the emergency spillway. maybe someone could write the company and ask them how they filled the voids.

Since this was posted as a reply to my comment about carrying capacity of concrete trucks, I assume it's a comment about that topic, which was the filling of voids beneath the slab (my apologies if I'm missing something here as I look at the various associated posts). I made the assumption that "void repair" would be performed without actually removing the slab, because only with the slab in place is the area to be filled called a "void". That's why I naturally assumed the specified 83 cubic yards for previous repair work referred to the use of concrete, or more likely, "grout", but that's just a special form of concrete having no coarse aggregate in the mix. Such material can be pumped under pressure to fill gaps beneath a slab. I apologize that I didn't even give thought to the idea that to someone outside of this branch of the construction industry might not automatically think along those same lines.

Here's one contractor's description of how this is done, but note that if "jacking" to raise a slab is not necessary (as seems to have been the case for former spillways repairs), the same process works for filling existing voids.

http://www.raise-rite.com/residential/concrete-raising/frequently-asked-questions/

Solid slabs of concrete can be raise and stabilized. Gravel areas or blacktop are unable to be repaired, and need to be replaced or re-installed to remedy settling issues. Slabs of concrete that are badly cracked may also be too damaged to lift.

If you are not sure if your concrete can be raised, call us for a Free Estimate. Raising settled concrete can be half the cost of replacing it with less damage to your landscaping and downtime. Our expert estimators will be able to assess and provide you with an accurate, FREE estimate for your project.

What is the difference between Mudjacking and Polyurethane Concrete Raising?
Both methods of concrete lifting will achieve the same results. Mudjacking concrete leveling and polyurethane concrete raising will raise and support sunken or unstable concrete slabs by drilling holes and pumping material under the slab.

Material
Settled concrete is commonly a result of poor soil conditions beneath a slab.

Polyurethane has become a popular repair method because the material is so lightweight compared to traditional mudjacking material, it will not further burden the already weak soil.

Mudjacking uses a sand based material that is infused with Portland cement. This slurry is hydraulically pumped under the slab to fill voids and raise the concrete. Mudjacking material weighs on average 100 lbs per cubic foot.

(Ignore the attached photo file of rip-rap. I can't figure out how to remove it in edit mode)

 

[Anna Reynolds]

A new DWR video breifly showing the spillway now that it is off.

Source: https://youtu.be/7fssz96ggCc


Screenshot from about the 0:45 mark

And approximately 0:55 mark

Compare to this screenshot from yesterday's video

Source: https://m.youtube.com/watch?feature=youtu.be&v=ixTg5Tgzeus


Also for comparison, this DWR photo from March 3, 2017

https://pixel-ca-dwr.photoshelter.c...00OPgqfQg5YIM/FL-Oroville-6921-03-03-2017-jpg

 

[jpal]

DWR's latest video indicates that they still cannot fully close down the spillway gates, just like last time. It appears that one or more gate seatings have developed some significant leaks.

They are getting significant flow with minimal head on the gates right now. As the lake level rises again, so will the head, and flow rate through any gaps.

It will be difficult to do any temporary, and nearly impossible to do any permanent spillway fixes with all that water flowing by. They may not be able to run the spillway dry until they can use the 13k cfs powerhouse alone to draw down the lake level below the spillway inlet, which may not be until sometime this summer. That could significantly effect the construction schedule.

 

[Peter Doe]

Here's a photo showing the rock anchors after 10 days of spillway use. Cavitation doesn't seem to be a problem.

 

[AlmostaCE]

Below is one of DWR's latest pictures of that section of the spillway. It's really not possible to tell if the flow of eroded material is coming from under the spillway (possibly through a hole in or under the shotcrete) but it seems odd that there is so much material in that one place.
View attachment 26059

As an afterthought, I suppose that if this was material coming from under the spillway rather than the bank in front of it, it might have been seen before the point at which the flow was reduced such that it was falling on that bank rather than shooting over it. On that basis the explanation quoted above is probably more likely to be right than this being evidence of water getting through the spillway deck despite all the recent caulking of it and flushing out material from underneath.

Based on the post closure pictures - this prominent plume of brown appears to be originating at the downstream edge of the shotcrete application along the left edge. You can see in the post shutdown photo that the area has been undercut which is indicative of the impact point and churning due to the lack of a "plunge pool" area to absorb and disperse the energy of the flowing water.

This isn't really surprising to me, nor particularly concerning - this type of erosion can be easily remedied and controlled with additional stone and grout rip-rap in the affected area between flow sessions of the flood control structure.

With regard to the gate sealing, they actually seal tighter with higher head pressure than they do with lower ones. In truth they really aren't designed for a 100% seal during normal operation so this leakage doesn't indicate to me that there is any issue there. Rotary gates are designed for flow control and modulation even with significant head pressures. It is possible with modern methods to make them also 100% sealing with inflatable bladder type seals, but this was something that likely wasn't readily available, nor was it a critical design feature at the time of construction.

 

[SFX]

Source: https://www.youtube.com/watch?v=7fssz96ggCc

Interesting.

 

[Boilermaker]

Looking at the photos posted above of the post-shutdown state of the end of the upper spillway, together with a few more from DWR's most recent photo uploads, there's something that may be pretty telling about the state of the spillway foundation. This is best illustrated by reference to the photos themselves.

Before the last shutdown, I understood Mr Croyle of DWR to say that it was intended to "shotcrete" the whole area of the splash pool. In the event that's not what happened and instead the face of the remaining spillway end rock foundation was what got the shotcrete treatment. The discrepancy actually makes sense if before the work started the decision was made to fill the splash pool with concrete as part of the final remedial effort.

But for some reason shotcrete was applied to a surface area that can be seen in the photos below, which is too large just to be overflow or excess from the rock foundation face. It lies on the extreme left of that area:

Before it was covered over, this area lay below what looks like a large cavity under the spillway deck. Below it is lot of fragmented rock/rubble, which I supposed when I saw this photo might have been washed out from under the deck when the spillway was running. That by itself would tend to indicate some considerable volume of water under the deck that was not being caught by the drainage system (despite the amount of water that was seen being discharged from the drains that emptied on to the deck):

Looking at the post-shutdown photos there's a perhaps rather telling feature evident, shown in this close-up. The shotcrete applied in the area forms a barrier or maybe a "crust" over part of it, which indicates that it prevented erosion of what was underneath, but to the near side of that area a deep gully has formed:

There must have been a natural fissure in the rock there to start with; this one looks as big as some of those that caused such concern when the attempt to use the emergency spillway was made. Although DWR is carrying out a geological survey of the area, at the moment there's reason to think that whole area is riven by features like this - and perhaps right up to the area of the spillway gates. Of course the Board of Consultants has recommended the reconstruction of both the remaining upper and lower spillway sections. You can see why if large parts of the structure were originally founded on ground like this. They'll be needing an awful lot of rock and concrete to do the job.

 

[David Jensen]

Just found this forum and it is excellent.

I am an engineer from Vancouver, BC and have been following the Oroville Dam situation closely (my greatest concern is the economic damage from the unleashing of an inflationary wave of national food price increases and consequent impact of interest rate increases on the economy from a dam failure in CA - not to mention the local human toll).

Have been trying to get my arms around the total scale of the problem. On the weekend, I put together the attached rough model in an .xls spreadsheet. Using these calcs and assuming 2' [feet] of water equivalent stored throughout the Oroville Dam catchment, this dam needs to exhaust 40,000 cfs of water for about 50 days this spring to pass the water now in the catchment. Not sure how accurate the 2' estimate is - some measurement stations in the Sierra have been reporting 6'+ of water equivalent in the snow pack - but this spillway needs to be serviceable for a considerable period this spring.

There is warm weather coming to this region in the coming weeks: http://www.accuweather.com/en/us/quincy-ca/95971/april-weather/331996?monyr=4/1/2017

 

[SFX]

They'll be needing an awful lot of rock and concrete to do the job.

It would seem they already have lots of rock.

 

[Tom W]

I was also expecting a full hardening of the plunge pool, kind of the building out of an angled ramp to allow the throttling back of outflows, but that didn't happen. Maybe this small ramp was a "test" of sorts, to see if it could work. Unfortunately, the only time it really took much of a battering was during those short periods when they were ramping up to 35,000 or so, and the times when they were throttling back to 0. At higher flows, the water was mostly thrown off the spillway into the gray rock of the plunge pool.

Looking at the photos posted above of the post-shutdown state of the end of the upper spillway, together with a few more from DWR's most recent photo uploads, there's something that may be pretty telling about the state of the spillway foundation. This is best illustrated by reference to the photos themselves.

Before the last shutdown, I understood Mr Croyle of DWR to say that it was intended to "shotcrete" the whole area of the splash pool. In the event that's not what happened and instead the face of the remaining spillway end rock foundation was what got the shotcrete treatment. The discrepancy actually makes sense if before the work started the decision was made to fill the splash pool with concrete as part of the final remedial effort.

But for some reason shotcrete was applied to a surface area that can be seen in the photos below, which is too large just to be overflow or excess from the rock foundation face. It lies on the extreme left of that area:

View attachment 26117
View attachment 26118

Before it was covered over, this area lay below what looks like a large cavity under the spillway deck. Below it is lot of fragmented rock/rubble, which I supposed when I saw this photo might have been washed out from under the deck when the spillway was running. That by itself would tend to indicate some considerable volume of water under the deck that was not being caught by the drainage system (despite the amount of water that was seen being discharged from the drains that emptied on to the deck):

View attachment 26121

Looking at the post-shutdown photos there's a perhaps rather telling feature evident, shown in this close-up. The shotcrete applied in the area forms a barrier or maybe a "crust" over part of it, which indicates that it prevented erosion of what was underneath, but to the near side of that area a deep gully has formed:

View attachment 26122

There must have been a natural fissure in the rock there to start with; this one looks as big as some of those that caused such concern when the attempt to use the emergency spillway was made. Although DWR is carrying out a geological survey of the area, at the moment there's reason to think that whole area is riven by features like this - and perhaps right up to the area of the spillway gates. Of course the Board of Consultants has recommended the reconstruction of both the remaining upper and lower spillway sections. You can see why if large parts of the structure were originally founded on ground like this. They'll be needing an awful lot of rock and concrete to do the job.

 

[Peter M]

We also have a pretty good idea how deep the plunge pool is, from this image. The shadow of the 'finger' of concrete sticking up from the lower spillway reaches all the way back to the deepest part of the plunge pool. With a little geometry, we'd know how far down that hole goes, and if we knew the time of day, roughly 5 pm, when the spillway flow stopped (sunset was at 19:45). But the answer is: pretty deep, even below the lower stretch of spillway. The hydraulic jump is absorbing a good fraction of the energy of the falling water, before it reaches the scour.

https://pixel-ca-dwr.photoshelter.c...Qrmo/DK-oroville-spillway-7295-03-27-2017-jpg

 

[FishOutofWater]

Looking at the photos posted above of the post-shutdown state of the end of the upper spillway, together with a few more from DWR's most recent photo uploads, there's something that may be pretty telling about the state of the spillway foundation. This is best illustrated by reference to the photos themselves.

SNIP for brevity....

View attachment 26122

There must have been a natural fissure in the rock there to start with; this one looks as big as some of those that caused such concern when the attempt to use the emergency spillway was made. Although DWR is carrying out a geological survey of the area, at the moment there's reason to think that whole area is riven by features like this - and perhaps right up to the area of the spillway gates. Of course the Board of Consultants has recommended the reconstruction of both the remaining upper and lower spillway sections. You can see why if large parts of the structure were originally founded on ground like this. They'll be needing an awful lot of rock and concrete to do the job.

The right side of the spillway (left side of the image looking uphill) was at a lower elevation than the right side before the spillway was built. Thus the right side tends to consist of weaker, more weathered material because the left side was excavated closer to the bedrock. Thus water flowing under the spillway made a channel on the right side.

This is a metamorphosed sheeted dike complex where the natural rock structure was originally close to vertical. I don't see evidence of a "natural fissure in the rock" in the images and videos I have watched. I see evidence of water flowing under the spillway which eroded channels in the red clay subsoil.

 

[Anna Reynolds]

It looks like Hyatt has been turned off as of 9am this morning.
https://cdec.water.ca.gov/cgi-progs/queryF?s=ORO&d=03-Apr-2017+10:21&span=25hours

 

[Anna Reynolds]

Found out why Hyatt was shut down for a while. http://www.actionnewsnow.com/story/35057508/oroville-lake-outflow-back-at-zero-again

[\EX] ...DWR officials told Action News Now Monday that the outflow was cut back for a few hours in order to allow for a survey of the diversion pool. Flows out of the Hyatt Powerhouse are expected to begin ramping up around noon Monday.[\EX]

 

[Mick West]

I'm going to close the treads in this forum, as they now only have interest to a very limited number of people. If you wish to continue discussion it can be done in the continuation thread in the members only Open Discussion forum where I've moved the last 100 posts.
https://www.metabunk.org/oroville-spillway-investigation-and-repair.t8640/