Notice that the gravel is rounded river rock. That had to have been placed there, over the bedrock. It is unlikely to have been on that rugged hillside, and it is not jagged gravel created from the bedrock. One of the drawings had a notation which was hard to read but seemed to refer to a layer over the bedrock.
This detail from page 170 shows that backfill concrete was used under the spillway slab. So in most places, the spillway slab rested on bedrock or backfill concrete, anchored every 10 feet into the bedrock or backfill. Where the slab was not on bedrock was where the drains were, where the clay drain pipes rested on gravel over the bedrock.
So there was no continuous bed of gravel which could carry water under the length of the spillway. That could happen in the pervious backfill on the sides, but the drains should pick up some of that water.
There is no gravel under the horizontal expansion joints, so if those leaked they should leak out the sides into the pervious backfill. However, the nine vertical expansion joints all cross the drains.
Well, in fact, what is pictured does appear to be installed properly, as it appears to be nearly exactly as the design document (HYD-510.pdf) called for (excepting that the drainage was upsized to 6"). If you are actually suggesting that it wasn't designed properly, your collateral also doesn't support that conclusion for at least two reasons:
The spillway design was completed 50 years prior to the date on the reference you provided, and therefore that reference could not have applied to the spillway design at the time it was done
The reference you provided appears to be applicable to the construction of highways, and not spillways
On the main thread Boilermaker #1395 posted a photo that might depict a feature of interest. In the first photo taken downstream of the break in the spillway, from the center to the lower right (kayak left) there is a sharp transition in the underlying rocks from red-brown to gray. Additionally the orientation of structures within the two rock bodies appear to be at different angles. From this perspective , at this location , it appears possible that the two rock types are not contiguous , i.e. the overlaying red-brown is not an altered portion of the gray immediately below. Any thoughts?
I post this here as it relates to the underlaying conditions upon which the spillway is built. I couldn't figure out how to post a hi-res version of that image here, nor how to insert colored arrows to mark precisely this transition.
SaC ~~
The point mentioned in my post that got deleted was,....that the drain holes in the VCP pipes that were installed in the spillway were placed to drain into the VCP from the top of the conduit as shown in the above post #161 and drawing shown in post #163. The holes in the VCP had a " Polyethylene Sheet " layer placed over the top of the VCP covering the up turned drain holes to prevent concrete from plugging them . This is clearly shown in the enlarged picture at the top of post #161 where a drain hole can be clearly seen at the disconnected opening of the VCP that I also expanded on my touch screen monitor. Perforated pipe conduits of various configuration VCP, PCP. metal construction have for the past 70 + years been placed with the inlet drain holes pointing down (AND NOT UP,.... IS MY POINT ) utilizing the back fill composition to filter out the fines before it gets into the drain pipe. The CalTrans drawing that is referenced above is typical of Highway Design and while not showing the location of any conduit drain holes in the drawing and / or whether the holes are to be placed up or down, the long standard of the industry is that the holes are placed DOWN .
Stuts
It isn't clear from the photo that the holes are all pointing up. Enlarged from the previous photo, below. The two holes that appear to be visible aren't facing up, so I don't see how your conclusion that the holes face up can be drawn from this photo.
I post this here as it relates to the underlaying conditions upon which the spillway is built. I couldn't figure out how to post a hi-res version of that image here, nor how to insert colored arrows to mark precisely this transition.
what does that have to do with drains?
(this question is not optional.. if it does not relate to drains, your post will be deleted)
Also in the future do not make people go searching through multiple pages for a photo. If you don't know how to screen shot an image see the "How to" forum" or google it.
At the VERY least give a link to the thread you are talking about and page number.
You can (and should in the future) click the # of the post you like, a box will pop up with the http link to that post.
SaC~
You are a hard nut to crack.
The drain Holes when manufactured are drilled / formed on the 1/2 +/- surface of the Circumference of the conduit as shown in the bell connection of the VCP ,................the second "bliminish" to the right of the picture is not a drain hole. Go to Home Depot and look at perforated drain pipe and ask which way to place the holes . You have beat this to the point of no farther response from me.
Re; Post #171 (Dierdre), "Dam Drains in Spillway..."Thread page 5
The link is post #1395(Boilermaker) page 35 in "Oroville Dam Spillway Failure". No privileges there to reply with. Did consult How To unsuccessfully. Apologies.
It appears my comment is in the quote box and might be mistaken for your content .
To be certain, the stability of the bedding material is a determinant in the functioning of the drains. Clay drain pipe is brittle and frangible . You can shatter it with a hammer. Movement in bedding ruptures drains.
no it won't. which is why using the MB reply functions and tags is important to conversation.
Whether you can reply to a thread has no bearing on linking. You just highlight the address bar and paste it into your post. or as I said, just click on the post number and copy the http:// address that pops up in the box.
Found this interesting.. it is another spillway contract to inspect drainage under spillway... I wonder if there are reports on file for the Oroville spillway documenting the inspections of the drains themselves.
An extensive system of sub-drainage and collector pipes (over 21,000 feet) exist beneath the approach slab, the ogee weir, the chute slab and stilling basin and behind the chute walls.
The pipes range in diameter from 3 to 12 inches. Pipe material types include solid and perforated PVC, solid and perforated vitrified clay pipe, solid asbestos cement pipe and perforated CMP. 1.3
Objectives: The overall objective of this contract is to thoroughly document the current condition of the sub-surface drains and collector pipes of the spillway structure. 1.4
Scope: Work generally consists of visual inspecting the drainage pipe (both vertical and horizontal) with remote-operated camera equipment and producing a detailed formal report to thoroughly document the condition of these features. To enable visual inspection of the vertical chute slab foundation drains (18 total), mechanical cleaning (brushing and flushing with water) will be required for these pipes. Deliverables from this work will include DVD(s) of the inspection footage and a report that summarizes the procedures and findings of all inspections and includes individual inspection logs that summarizes the condition each pipe segment and documents the location of any significant observation.
The Contractor shall perform these services as noted in this PWS. All work shall be conducted in accordance with current professional standards, Corps of Engineers policies, regulations, and procedures. The Contractor is responsible for supplying all equipment, supplies, materials and personnel necessary for the completion of this work. 1.5 Scope Period of Performance: The period of performance for the PWS shall be
From this I have zoomed and annotated the following image:
Based on what we see here, I believe the following to be true -
The entire system, up to and including the sidewall outlets is composed of VCP (Vitreous Clay Pipe)
The vertical shafts visible along the sidewalls appear to be the points at which the longitudinal drains that collect the lateral under-slab drains makes the transition to the upward (in reality almost horizontal) pipe to reach the sidewall drain outlet. I expect these exist for cleaning and inspection purposes.
You can see in the photo 2 of the lateral drains exiting under the sidewall grade-beam - I surmise that the longitudinal drain here is missing due to damage - it likely exists upstream under the debris as noted.
Overall, I found this photo to provide good information on the assembly of the system.
This view and the one directly above, in post #177, appear to show a line on the outside of the sidewall from the drain tile in the backfill to the fitting through the wall. I am guessing it is a construction line to show the level of backfill prior to placing the connecting pipe to the wall drain.
Could the angle between that line and the top of the wall be determined to see if it resembles the angle that the spillway decends the hillside?
...
You can see in the photo 2 of the lateral drains exiting under the sidewall grade-beam - I surmise that the longitudinal drain here is missing due to damage - it likely exists upstream under the debris as noted.
This view and the one directly above, in post #177, appear to show a line on the outside of the sidewall from the drain tile in the backfill to the fitting through the wall. I am guessing it is a construction line to show the level of backfill prior to placing the connecting pipe to the wall drain.
Could the angle between that line and the top of the wall be determined to see if it resembles the angle that the spillway decends the hillside?
The horizontals are spaced to what appear to be plywood form lines at 4 ft; also consistent with 20 ft tall wall. In Post #42 I estimated fence pole spacing at 10 ft. This places the vertical slab lines on 25 ft centers.
Downhill from the change in spillway slope, the slope is a constant 25% - drops 25 ft in every 100 ft of horizontal. So a horizontal line would climb approximately 6 ft in 25 ft -- or it would climb one and a half 4ft sections between two vertical form lines. I have drawn that in heavy dotted. It looks weird to me, but that is because the photo is so heavily foreshortened, both due to angle and use of telescopic lens.
The "pencil line" on the wall between the pipe in the fill and the elbow on the wall is almost exactly parallel to my estimate of hoizontal.
This picture gives an excellent view of wall and form dimensions -- note slab seam running directly through camera - so the wall is perpendicular to line of sight. (Although it is tilted -- scaffold is vertical.)
Very nice work, this is exactly what I was hoping someone could and would do. I would say that the mismatch between the "pencil line" and your line could easily describe the necessary slope for the pipe to get the water to the wall drain properly. I believe you have shown that the "pencil line" is actually a guide line for the original construction crew as they placed the backfill for the pipe to rest on when it was installed.
It also looks like an extension of your line would intersect the vertical pipe farther upslope about at the bottom of the spillway. Very nice work.
Slope of the spillway should be a matter of record; and applicable to the top of the sidewall, to preclude the need to estimate the horizontal in post#180.
Slope of the spillway should be a matter of record; and applicable to the top of the sidewall, to preclude the need to estimate the horizontal in post#180.
... I would say that the mismatch between the "pencil line" and your line could easily describe the necessary slope for the pipe to get the water to the wall drain properly. I believe you have shown that the "pencil line" is actually a guide line for the original construction crew as they placed the backfill for the pipe to rest on when it was installed. ...
I can't see any significant difference in slope between the line I estimated and the pencil line. Recognizing my coarse methods, I cannot tell whether the pencil line is actual horizontal (as could easily be laid out w bubble levels) or is the desired drain line slope. Either way there is not much difference as evidenced by the relative positions of the two ends of the pipe. That section of drain line is gently sloped.
That's pretty rough. Keeping in mind the longitudinal drain is closer to the wall than the vertical or horizontal runs, it appears the horizontal branches off the outside of the longitudinal, then the vertical wyes into the horizontal. Use of a wye to branch off the horizontal drain from the longitudinal would be using it in the reverse of its normal use. Normally the wye branch arm carries inflow, not outflow.
Your image is good but I think the drains are a little different. I hope my poor art work shows how I think this system works.
There are what appear to be broken drain pipes in the red circles, one under the spillway and a collector running along the path of the green arrow down the hill to the next wall drain.
I believe the blue pipe marked with the red X is incorrect even though some of the original drawings show a pipe in that location. I don't know of any way to connect it to the under slab pipes without asking the water to go up from the underslab to the collector. That would be very unusual in a gravity drain system. The under slab pipes could run downhill a ways before connecting with the collector but it appears that method would require much more complicated connections and piping.
I believe the left red circle is around the end of the collector pipe outboard and just below the slab and the right red circle is around the end of an under slab pipe. I believe the collector is not continuous but runs down hill until it turns near horizontal and connects with the next wall drain. Another collector begins at the next under slab pipe. As mentioned earlier in this thread, a continuous downhill collector run would allow very large pressures to develop, something the clay pipe is not so great at dealing with.
I agree that was what appears to be the original design intent.
Here is why I don't believe that is how it was ultimately constructed:
Such a position for the longitudinal drain would have made for unnecessarily complicated connections from the lateral "herringbone" drains into the collector. If the collector was "in plane" with the laterals (along side the grade beam), a simple Wye fitting would have allowed connection.
Ultimately, barring some excavation and photos at that point, we won't know the actual configuration installed, but I question why the original constructors would have made their jobs more difficult than their task already was.
I view the construction drawings like so many sets of plans I see in my day job - it looks good on paper and makes sense to the architect/engineer, but when it comes time to build it, there is a more straight forward option that doesn't sacrifice function.
As mentioned earlier in this thread, a continuous downhill collector run would allow very large pressures to develop, something the clay pipe is not so great at dealing with.
Not only this! If there's a continuous downhill collector, inner pressure will eject water in all directions beneath the actual water level, both into the outlets and into the intakes (perforated sections). The water will flood the under-slab space, and at some lower elevation it will act as a water-jetting device.
"Estimated horizontal" appears off. Based on the photo (post # 180 Orville Dam Drains Thread ) of the scaffolding in the spillway, assuming the scaffolding is vertical , true horizontal diverges from spillway top at ~ 15 degrees (+ - 2 degrees). The "estimated horizontal" diverges from the spillway top at ~ 30 degrees (+ - 5 degrees). Based on this the estimated horizontal is rising ~ 15 degrees towards the downstream.
If the system here is a gravity drain , I would expect the outlets (holes draining plumes of water into the spillway) to be the lowest point in the system . This might not be the case and they may indeed rise from the "manhole/cleanouts"
One additional missing piece of information that may tie this together is, where is the transition from 6" underslab perforated drain pipe to what appear to be larger (12"???) outlets along the spillway walls?
As a (retired) water resource engineer I have been intrigued by the design of the drains and their likely role in the spillway failure, and am impressed by the effort all have made. Barring better record plans it appears the lateral drains connect to a longitudinal drain outside and near the bottom of the footing, which follows the footing downstream and collects more lateral drains, then joins a vertical inspection/clean out pipe (capped and protruding above ground at intervals as shown in several of the photos, near the wall, and then turns almost horizontal along the line visible on the wall to the 90* elbow through the wall. A new collector starts at the next transverse drain.
What is truly impressive is the amount of flow in the drains - way more than I would expect. There are lots of cracks in the spillway visible in the curios photos, and many of these are at a diagonal following the transverse drains (check GoogleEarth), which occupy about 6 inches of the 15 inch slab thickness and create an obvious plane of weakness. This would explain the large flow. In the event that a longitudinal drain fails or plugs, pressures will rise as much as the water level at the mist upstream drain in the chain. In that event the lateral drains perversely allow the water to flow backwards and to develop enough pressure to lift the slab. There is minimal reinforcement of the transverse joints - only short bars spanning the joint, and they are located near the bottom of the slab and have minimal resistance to spalling if the slab if lifted. The rest is history.
After a long conversation with a friend who has much experience with plumbing and drain systems, I have changed my idea of how this system works.
He explained that the collector more likely starts with the first under drain below the near horizontal connector that goes to the wall drain opening. The vertical vent pipe likely connects to the top of the collector section at or near the most uphill under drain where it clears the edge of the spillway.
His explanation was that the top of the system needs to be vented, to prevent any suction forming in the collector as it proceeds downhill and there would be considerable pressure in the piping at the bottom of the vent if it were connected as I first proposed. That would prevent any air from flowing downward in the vent to assist with the drainage.
If the drains are configured as sweepleader proposes above (vent tube at the high end, then side drains, with exhaust port at the low end), then it appears that there may be some Q&D tests which could've been done 50 years ago, and every year since, and might still be applicable today.
A simple pressure test: you plug the downstream exhaust port, and pour water into the upstream vent tube. For a new healthy drain, a known (calculable) volume of water would quickly fill the pipes, then a larger volume of water would more slowly fill in the under-slab gravel filters. If only a little water goes in, this indicates the pipes are clogged or cracked. If too much water goes in, this indicates voids have formed adjacent the drainpipes.
If this pressure head is held long enough, water should perk back up into the slab, with the wet spots indicating potentially previously unseen flow pathways. This could also be used to validate the efficiency of slab water sealing methods (which to date apparently haven't been too effective).
For drains that can not hold a pressure head, various tracer chemical salts could be added to the water to determine what percentage is migrating into adjacent drains, and therefore how much is exiting via unknown pathways. With the right tracers, it may even be possible to determine where the missing water reenters the river. A “map” of the underflow pathways could be quite useful.
When the sidewall plug is pulled out, the exit water could be evaluated for turbidity. Any suspended solids in the water indicates that much less backfill under the slab.
A key question for the State is: do they simply seal the upper spillway, reinforce it with more concrete, or rip it out and replace it. Having a better understanding of these subsurface drains aids in that assessment.
The dam is at a nearly 30 degree slope; images of scaffolding erected by the sidewalls show this, as does the original blueprint. Add in foreshortening from the perspective, and the apparent angle becomes more pronounced. In short, you are almost certainly basing your report on an optical illusion.
Does anyone know the source of the second image. I know I posted it but I can't find where from. Possible I found it on something like Panoramio where it no longer exists. It looks a bit like either a video still, or a clip from a much larger overview image.
I'm trying to verify the date from someone investigating the failure.
