Any above ground unrestrained bell & spigot joint for thrust block? 1

[Bbird]

I have come across a bell & spigot joint pulling out in front of a thrust block. Except for a small concrete plinth supporting the dead weight of the pipe body the joint has not been restrained and is part of an above-ground installation to a 62" welded pipe system. The below ground portion is bell & spigot throughout after the thrust block.

Can anybody point out if such practice, of having above ground unrestrained bell & spigot joint, is widespread? or if there code or good engineering practice that disencourage such installation? Some previous examples if exist would be appreciated.

 

[PUMPDESIGNER]

I deal with your systems all the time in large irrigation systems. For short we call it "gasketed pipe".

I personally have been frustrated by the seeming inability of field workers to understand the concepts of transferring thrust loads from the pipe into the ground. They continue to think that the dead weight of the concrete is the restraint, even after you prove to them that the concrete is a thrust transfer mechanism, not a dead weight stop.

Anyway, ASAE has design and install standards for un-restrained pipe systems (ASAE S376), which may be based on ISO standards, I am not sure.




PUMPDESIGNER

 

[Bbird]

pumpdesigner,

Thanks for the reference. However it is for thermoplastic underground irrigation pipeline for maximum pressure upto 315 psi or about 21 bar. The failed pipe is ductile iron and is rated at 26 bar.

I would appreciate any feed back on if such practice is widespread.

There is also something illogical too. At such a high pressure there will be a significant longitudinal stress set up in the pipe wall equal to

Internal pressure x diameter / (4 x wall thicknes)

Surly this stress has to be restrained fully before and after the bell and spigot section of the above ground pipeline otherwise the system will not work.

 

[PUMPDESIGNER]

Sorry 'bout thatn Bbird (Like that handle).
I often get onto this forum when I am worn out at the end of the day and just looking to relax for a few minutes, let down all my guard and get carefree but careless too.


PUMPDESIGNER

 

[BobPE]

Bbird:

Above ground bell and spigot is a unacceptable design as you seem to be finding out...For the bell and spigot joint to function it must be restrained and usually soil is used for this purpose, making this joint cost effective for underground installation. The pressure inside the pipe is what is causing failure of the above ground bell and spigot joint. In my opinion, I would have to think this to be a dangerous situation you discovered depending on the forces involved and no matter what, needs to be addressed. If you are unsure, serve as the agent to get some professional engineering assistance to come up with a safer design.

Let us know how you make out....

BobPE