Pipe Stiffness vs. Pipe Rigidity 1

[samond]

Can someone tell me if there is a difference between stiffness and rigidity of a pipe? I understand that pipe stiffness is used to describe the load vs deflection relationship. We are planning on sliplining an 18" pipe inside an existing 48" pipe and have it "float" via grout to the crown of the top of pipe for approximately 5,000 LF. I will have a simply supported pipe, for lack of a better term, spanning between 400 to 600 feet from manhole to manhole. Skids or some sort of support will be located at each manhole to keep the pipe at the crown of the pipe. There will not be any weight bearing from backfill on the pipe to cause deflection, so I am not sure if I need to compare stiffness specifications. If not, I am not sure what the correct property is that I need to compare to see which pipe would sag the least in the large of a span. I am considering Hobas, polyethelene, and any other that may be suggested. I know that PE pipe is very flexible so I am concerned that grout may get between the crown of the 48" pipe and new sliplined pipe and create a major sag. In any case, I want to make sure I am asking the right questions and exhuasting all possibilities.
Thanks in advance for any advice.

 

[dicksewerrat]

Seal the slip line pipe at both ends and start pumping your grout. The pipe will float up. Once you see the grout level get to about 10 inches from the top of your 48, stop pumping and let grout set up. Then finish the grouting. You will have to do this for each section.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[LittleInch]

I will stand to be corrected, but my view is that the terms are commonly interchanged and essentially the same.

The issue for me is why you want the pipe to be at the crown of the big pipe rather than the base of the pipe? 18" inside a 48" is a pretty loose fit and with the initial spanning your pipe may snake a bit when floated up to the top.

For a PE line you would probably need supports every 20ft or so clamped to the pipe and dragged in with it. Most supports like this are intended to centralise the pipe so you would need to figure out a way of keeping the pipe on the top if you really wanted to be sure it was at the crown.

Once you've grouted it though you're stuck with it. Why don't you instal bundle of pipes slightly less than 48"and weigh down the bottom one with a chain or something to stop it twisting so your 18 line ends up on top??. Much less grout and you have 2 or more spare conduits for cables, fluid or just spare. It seems such a waste to fill the 48 line with that much grout and not use it for something else. Other utilities are always looking for ducts.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way