Shallow trench C-900 Pipeline restraint

[dmrsch]

Hello to all and TIA.
I have an application for a temporary pipeline of C-900 PVC pipe. The run is 1300 ft long, the trench is three ft deep the back fill WILL NOT be compacted as it needs to be removed. Should I require the contractor to restrain all the joints?

 

[civilperson]

Backfill that is not compacted is a mistake. Compacted backfill can be excavated as well as native soil. No compaction in the backfill lessens the system strength of the pipe and threatens the integrity for imposed vertical loads as well as internal pressure.

 

[dmrsch]

I have spoken to industry reps, which have informed me that we should restrain all joints

 

[LCruiser]

Temporary C-900 for 1300 feet? Why that expensive? What is it for?

 

[rconner]

I was just curious as there is not much info given -- did the "industry reps" require that "all the pvc pipe joints be restrained" due to the three foot trench, or the lack of compaction, or for some other reason/combination? (This requirement sounds like it could represent some significant expense, particularly if some kind of dependable harness devices must be purchased.)

 

[dmrsch]

There is alot of expense with this application.
There is a potential of a higher than normal flow and velocity in the pipe. Therefore due to this and water hammer it was decided that we should restrain all the joints

 

[rconner]

Interesting - however, it might behoove one to be cautious in perception that just a provision for joint restraint would make such systems suitable for very high velocities or water hammer (see e.g. threads

http://www.eng-tips.com/viewthread.cfm?qid=167516&page=9

and

http://www.eng-tips.com/viewthread.cfm?qid=132053

etc.)

 

[DMcGrath]

Why not use HDPE pipe? With the fusion welded joints, they are by definition fully restrained. The welding process makes the joint at least as strong as the pipe itself. See

http://www.leesupply.com/products_technical_notes.html

and go to "About Performance Pipe" chapter.

 

[LCruiser]

What is the application?

 

[blueoak]

I am curious about how temporary, what is the purpose, and is it critical (can you run out and fix it). I have seen and done some temporary without trenching. Made it a whole lot more temporary.

 

[rodhouser]

I agree with your decision to restrain all of the joints. With only 2-ft of cover the soil will not have much passive strength to support a thrust block.

Don't bother with calculating the required restrained length because with uncompacted backfill there won't be enough skin-friction to count on; restrain every joint. For a pipeline that's only 1300-ft long the incremental project cost of restraining every joint will be insignificant.

DIPRA (Ductile Iron Pipe Research Association) distributes a free thrust restraint program, and a very nice pamphlet on this topic - the principles of thrust restraint are basically the same for PVC and ductile iron.