UG HDPE pipe- thrust block req'd ?

[davefitz]

Kidnly advise your educated opinion or advise a design manual that would apply to this case:

1500 ft of 12" NPS HDPE pipe, 2 ft of cover, installed in a soil of normal soil temp of 55 F. The pipe will accept blowdown slurrry water from a FGD system, at 120 F, cycled twice per day. Engineer of record not sure if any thrust blocks are required. Is there a AWWA design code that can be used to govern this decision? AWWA M55 ?

Will this pipelook like a half submerged dragon after 10 cycles?

 

[DMcGrath]

Driscopipe, one of the major manufacturers of HDPE pipe in the US, states throughout their design manual that thrust blocking at pipe joints is not required due to the nature of the fusion welding process for joining HDPE pipe. The fusion joining process (when done properly) produces a joint that is at least as strong as the native pipe. Have a look at pages 10 & 11 here:

http://www.cpchem.com/enu/docs_pipe/PP501WaterDistribution.pdf

 

[blueoak]

Working with a mining company, they have no problems if they bury it. The fusion welding seems to hold well so burying keeps it from rolling all over the place. Seems lateral constraint has been their concern with it for slurry.

 

[bimr]

No. You do not have to even bury it. You can leave it on top of the soil if you like.

http://www.isco-pipe.com/reference_center/pipe_specs.asp

 

[stanier]

No thrust blocks.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[BigInch]

No thrust blocks, as the thrust load is transfered through the fused joint and is balanced by axial stress in the pipe. Axial stress in buried pipe is eventually disipated by cohesive and friction forces into the soil. In unburied pipe, only contact friction between pipe and soil would be available.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[StephenA]

There is a caveat to bimr in that PE pipe has a high coefficient of expansion and the pipe, if not buried, may move over the ground with temperature change.

Stephen Argles
Land & Marine

http://www.landandmarine.com

 

[stanier]

Be aware that large PE tees are fabricated using hot extrusion guns. They do not have the reinforcing that you would see in a steel tee designed to AWWA M11.

There is a weld derating factor of 0.8 for the tees if the welding is carried out by a qualified welder.

A hydro test isnt necessarily going to prove the integrity of the fitting.

I have seen large tees concrete encased after a leak or just in case. In any event the concrete block wasnt for thrust but to prevent further damage to the tee and to stop the leak.

If you are going to encase in concrete there is a need to wrap the tee with a rubber material (wet suit type).

As for thrust, if the tee were aboveground would the mechanical engineer concrete encase it? No, of course not. This is the way I explain the concept to civil engineers who dont grasp the idea that they need everything coloured "grey".

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au