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  1. sweepleader

    sweepleader Member

    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.
     
  2. EricL

    EricL Member

    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/



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

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    Last edited: Mar 29, 2017
  3. Anna Reynolds

    Anna Reynolds Member

    Last edited: Mar 29, 2017
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  4. jpal

    jpal New Member

    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.
     
  5. Peter Doe

    Peter Doe New Member

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

    [​IMG]
     
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  6. AlmostaCE

    AlmostaCE New Member

    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.
     
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  7. SFX

    SFX Member

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  8. Boilermaker

    Boilermaker Member

    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:

    IMG_8710.JPG
    IMG_8711.JPG

    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):

    IMG_8707.PNG

    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:

    Waterfall.

    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.
     
  9. David Jensen

    David Jensen Closed Account

    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
     

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    Last edited: Mar 30, 2017
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  10. SFX

    SFX Member

    It would seem they already have lots of rock.
     
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  11. Tom W

    Tom W New Member

    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.

     
  12. Peter M

    Peter M New Member

    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
    deephole.PNG
     
    Last edited: Mar 31, 2017
  13. FishOutofWater

    FishOutofWater New Member

    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.
     
  14. Anna Reynolds

    Anna Reynolds Member

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  15. Anna Reynolds

    Anna Reynolds Member

  16. Mick West

    Mick West Administrator Staff Member

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