Restrained joints in casing
Restrained joints in casing
(OP)
Hi - I'm checking opinions. I'm designing a C900 PVC pipeline (12") for potable water distribution that is going across open ground in a straight line, and then crossing a highway in a bore that will have a jacked steel casing. The pipe within the casing will be mounted on centering skids. My questions are: (1) Do I need restrained joints within the casing (pipe outside the casing has enought straight laying to not need restraint). (2) Is PVC the appropriate material within the steel casing? (3a) Do I need to fill the annular space within the casing? (3b) With grout? (3c) Blown sand?
Thanks
Thanks





RE: Restrained joints in casing
RE: Restrained joints in casing
No you do not have to have restrained joints. You do however have to affix spacers to the C-900 and ensure they fit into the casing. Match OD of spacer to ID of casing. Also, ensure your casing is large enough to accomodate the OD of the bell on the pipe, very important. PVC is absolutely fine and the approach you are taking is absolutely correct.
When case boring, make sure the contractor is aware of the huge undertaking and space required to do the case bore, particularly a large area to stockpile the augered soil with a loader. Determine who is to pay for the crane as well (one contractor I knew had no clue about the operation and it got very ugly).
KRS Services
www.krs-services.com
RE: Restrained joints in casing
The pipe will be burried - by "going across open ground," I meant to imply that I had enough straight run and soil friction outside the casing that restrained joints weren't necessary. Perhaps I should learn to write what I meant to imply.
Keith
RE: Restrained joints in casing
1) Restrained joints are generally not needed in the casing.
2) PVC pipe in a steel casing is fine. See http://www.ipexinc.com/download/pdf/pvcinstallguide.pdf for a guideline on casing sizing and the required spacers. For spacers, you can always strap some 1"x2" to the pipe (assuming of course that the strapping will extend out past the bell of the pipes so the pipe is resting on the strapping) if you don't want to buy the manufactured spacers.
3) As for filling the anular spacing, you need to ask a couple questions...
a) Why is there a casing in the first place? If the casing is to prevent the water from eroding the road in case of a watermain break, you want the casing empty so that the water can flow to either end and discharge somewhere else.
b) Does the road authority have the requirement "Loads shall not be transfered to the carrier pipe."? If they do, then again, you can't fill the space.
c) You will need to do something at the ends of course. In the past, we have just used a few cans of spray foam sealer and sealed off the last 12" of the pipe. It doesn't transfer load and if there is a break, the water pressure will pretty much blow an opening in it. The only concern ever expressed was whether the foam would react with the PVC pipe but we got a statement from the foam manufacturer that their product was inert and wouldn't react with the pipe.
David Dietrich
Thames Valley Engineering
RE: Restrained joints in casing
Next do you need a steel casing or just a casing. The reason I ask is that if just a casing is required (by any road regulations) then possibly a plastic (HDPE?) casing could be used.
I suggest that an HDPE casing is used, installed by HDD and after an HDPE pipe is passed through.
Zambo
RE: Restrained joints in casing
As for whether to fill with sand or grout, either is probably fine. There are arguments either way: sand can be removed if there is a leak, but if it's grouted, will it ever actually leak? Personally, I like sand as it allows for repairs if necessary. Some situation will always arise that none of us thought of and its better to maintain flexibility.
RE: Restrained joints in casing
RE: Restrained joints in casing
If it is bell and socket, think again, have you considered infiltration due to negative pressure.
If the pipeline is changing its alingnment before and after entering the casing, provide Thrust blocks.
Amar.
RE: Restrained joints in casing
PVC pipe is fine for casing applications, as long as the pipe meets your system requirements.
Fill the annular space. Grout is generally preferred. Recommend using mechanical casing spacers. Wood that is creosote treated will damage the pipe. Good luck.
RE: Restrained joints in casing
RE: Restrained joints in casing
check out www.driscoplex.com, good luck.
RE: Restrained joints in casing
Include vents at each end of the casig pipe. We construct ours out of 2 inch PVC and put a goosneck with insect screen on the top of each vent pipe. This way, if there's a leak it'll surface in a visible way.
Your casing pipe should be installed so that it can drain to one end. Condensation can build up in the casing pipe and cause corrosion over time if it can't drain out of the pipe.
Good luck with this project (which may be complete now??)