Replies

Hello, ER333,
...regarding the 6 inch vitrified clay pipe...
is that 6 inch ID or 6 inch OD?
Do all of the previous drawings and analysis
also take into account the size of the female end flange?
which can add another two inches to the diameter?
(I have laid a bit of this in a past life)
We could be talking about a total of 8 inches
or greater reduction in the thickness of the slab.
I do not understand the logic of making a permeable drain and
then deciding to cover it with an impermeable plastic wrap.
It just does not make sense to me.
I also do not understand why the drains were not located
directly under the slab joints (control joints)
where leakage would be most likely expected to occur.

Repeal The 17th, abb, meyer, Sorry I couldn't get back to you on your questions & discussion (an emergency came up). I looked at the original Oroville scale drawings and was able to extract good values on the I.D., O.D., and thickness of the 4" drain pipe in the original design.

Rather than catch up individually on posts, I put a single image post together as a response & new graphic of the slab thinning.

Good Work --- back to one of the questions...

"I do not understand the logic of making a permeable drain and then deciding to cover it with an impermeable plastic wrap. It just does not make sense to me."

If you look at "Standard Perforated Pipe", on page 5 of the catalog, the drain perforation holes are oriented in the lower half of the pipe. I do not know if this was the case with the Oroville drain pipe as only one hole is visible in the image (at the 9 o'clock position). Using Polyethylene plastic to cover the crest of the drain pipe would serve the designer's intent IF the surrounding drain rock were to maintain its intended sloping shape, like a pyramid.

The drain system is intended to capture any water that penetrated into the lower seam, or the bottom, of the spillway slab (via cracks, or leaks in the abutting slab seam edges). Drainage also is to target any water that seeps into this seam from sources below the spillway slab.

Modern drain designs have a lower notched capture area below the slab bottom layer (see post 2,239 for Modern Drain design). This is what Oroville should have done. But, doing a notched system for the full 3,055ft length of the spillway would have been a significant construction effort as it would have needed to be cut into the foundation pours and the bedrock areas.

I really wonder what type of discussion occurred on the Oroville slab drain design....