Subgrade Modulus for a Pipeline

[nicka70]

The project is for a pressurized pipeline that will go between 5 ft to 25 ft below ground surface (depending if they do HDD or trenching). The pipeline extends for about 6 miles, so there is a large variation between materials along the plan view.

The hydraulic/civil engineer want subgrade modulus of the soil along the alignment. They want the subgrade modulus to possibly allow a cheaper/weaker pipe along sections with a high subgrade modulus. I can provide them these values based on correlations and soil type (as you would for a mat foundation) but I've never used these correlations for this application. The pipe will apply stresses both vertically and horizontally on the soil so I will have to provide a subgrade modulus for both directions.

Can anyone provide insight to this? Has anyone come across this before? Any publications you can direct me to?

Thanks

 

[SlideRuleEra]

You did not mention what type pipe is being considered. Different pipe materials (e.g. steel, ductile iron, concrete, high-density polyethylene, fiberglass, etc.) and various joint types (e.g. welded, push-on, mechanical, flanged, fused, etc.) have different bedding requirements for assorted reasons.

Since you are able to provide the requested information, if you do so, and then follow-up with the hydraulic/civil engineer, you may get the answer to your questions from that engineer.

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[LittleInch]

I think in terms of steel pipeline and the only time this would be important is for stress calculations of high temperature pipelines which need to move at bends to reduce locked in stresses. in this case normally low strength soils are better, but otherwise I'm having difficulty seeing where it could be used to justify thinner pipe.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dicksewerrat]

See ASTM D3839. Also flexible pipes push out on the soil as it flattens due to vertical load. Stiffer soils slow the ovalization of the pipe. Check Spangler and Iowa state for more info. That said, I wouldn't use a "weaker' pipe to move explosive or flammable fluids.

Richard A. Cornelius, P.E.

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