Fully restrained water pipeline?

[salsman]

Hi All-

I am looking at a project in southern California and the 24" Ductile Iron Potable water pipeline is shown as having fully all joint restrained. The pipeline has straight section several hundred feet long. I am wondering why the designer would indicate full restraint in the straight sections. I am not yet completely familiar with the design considerations of Southern California; is this due to seismic forces? Is this common here?

Thanks for the help!

 

[BigInch]

Or .. high temperatures, or high operating pressure.

Independent events are seldomly independent.

 

[rconner]

I guess there could be different design, installation and/or operational reasons, including future plans for the system or modifications, why this has been so specified -- therefore, it may be best to ask the project designer. That being said, it is my understanding standard DIP has traditionally performed very well compared to other pipes in earthquake events. The pipe itself is tremendously strong and ductile as a "beam", though some traditional joints intended for underground service are also quite flexible meaning that the individual pipes can move relative to each other in response to ground waves or relative movements of ground or structures, even before that tremendous beam strength is challenged. Some authors have likened such favorable structural features to the behavior of "chains" (with the links able to move relative to each other without really bending the steel).

However, even though modern rubber-gasketed sockets can tolerate quite a bit of deflection and pull-out, there have been at least a few joint "pull-out" separation/leaks of unrestrained pipes in some soil environments in at least a few substantial earthquake events, where that specific soil mass was subject to excessive "lateral spreading" (and local "fissuring"), or substantial localized/relative ground movements or subsidence etc. Modern ductile iron restrained joints have multiple features that can be quite helpful in such cases, including some axial extensibility/extension (space in the joints, to absorb tensile and compressive ground waves without much challenging great compressive strength etc. of barrels), joint flexibility (ability for pipes to digress off the line of each other with movement in the joint, again without challenging great beam strength), as well as great tensile strength restraint capability to quite positively prevent separation (that allows joints that might be near a wide local fissure to mobilize/pull significant lengths of pipe on either side some though the ground, again without leaks or separations). Modern loose polyethylene sleeving or wrap, used now mostly for standard corrosion protection of ductile iron piping in potentially corrosive soil areas, aids further in this load distribution/mobilization process, acting as a sort of pipe-to-ground lubricant to the restrained joint piping.

 

[cvg]

in my experience in SoCal, 95% of the water pipelines we designed were CML&C, not DIP and none were fully restrained. none had high temperatures (except some geothermal lines which really weren't all that high) and maximum normal operating pressure of 120 psi. For installations directly over an active fault, it might be useful to restrain the pipeline further, but I have not seen it required by the water districts even within a few miles of either the San Andreas or the San Jacinto fault zones. Given the difficulty in precisely locating a fault rupture zone, not sure you could define it within just a couple hundred feet.

If this line is located near potential liquifaction areas, than that could be a valid reason for additional restraint.

Now, given that things might have changed since the Northridge, Landers and Big Bear quakes. Additional resiliency is likely being designed for all underground utilities.

 

[salsman]

Thanks, all that makes good sense. Have you heard of using all restrained joints as a municipality policy or local design requirement in seismic zones? I have always just designed using the DIPRA restrain joint length method here:

http://www.dipra.org/content/uploads/Design-Thrust-Restraint.pdf

But I could see the reasoning behind restraining all joints in seismic zones. These articles discusse what they are trying in LA:

http://www.kubota-global.net/us/news/2012/20121022.html

http://www.dailynews.com/news/ci_22641789/earthquake-resistant-pipes-may-bring-leak-free-l

 

[fel3]

I spent 5 years myself in SoCal in the early 1980s and designed several miles of CML&C pipe ranging from 14" to 24", but did only about 2000 feet of DIP. Design pressures for the SML&C ranged up to nearly 300 psi. For the larger pipes we relied on pipe-soil friction instead of concrete blocks for thrust restraint, which meant welded joints for some distance each side of a bend. Past that, we went back to rubber gasket joints. Could it be that the other engineer was restraining the joints for thrust restraint?

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[salsman]

Thanks for the info! It is not in a fault and the restraint far exceeds what would be needed for thrust, so I will have to ask the designer.

Thanks

 

[dicksewerrat]

you could use Mega Lug Mechanical joints on the straight sections. But it looks like overkill to me.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com