B31.4, API RP 1102 - Highway crossing, ASCE Guidelines for the design of buried steel pipe

[AlbertaMecchie]

Wonder what experience folks might have out there with B31.4, API RP 1102 - Highway crossing, and ASCE Guidelines for the design of buried steel pipe.

I am evaluating a slurry pipeline, which will be buried, and will have Cat D8s crossing over it. Where the D8s go over it the pipeline will be covered with coarse sand with unit weight of 120 lb/ft3. The pipe will be above the water table under about 3.3 feet of sand cover.

I was thinking of using API RP 1102 to do the evaluation, however would this even be applicable or relevant ? Cat D8s are tracked, they don't have axles / wheels. Ground pressure from D8 tracks is about 13.3 psig. Typical applied surface pressure for single axle in API RP 1102 is 83.3 psig. So I figure using the 83.3 psig could be quite conservative.

API RP 1102 calculates an effective stress and typically the evaluation incorporates a design factor of 0.72. B31.4 however, for slurry pipelines allows for a general design factor of 0.8, and under C403.3.1 states that sum of longitudinal stresses produced by pressure, live and dead loads, and those produced by occasional loads shall not exceed 88% of the yield strength of the pipe.

So I am wondering if anybody can provide any feedback. I was also looking at ASCE Guidelines for the design of buried steel pipe, I was thinking I could use this instead of API RP 1102, and calculate the stresses in the buried pipeline from the through wall bending stress due to vertical earth load pressure + D8 ground pressure (live load), restrained pipe longitudinal stress including thermal expansion, and hoop stress from internal pressure using the B31.4 Maximum Distortion Energy Theory under 402.7. The piping is not subject to impact loads, buoyancy, wind, earthquake or transients.

Thanks !

 

[1503-44]

Tracked vehicle pipeline stresses are usually not a problem. The problem with tracked vehicles is deterioration of the surface over the backfill, as they do tend to leave the surface sliced up, from which water easily gains entry into the backfill. Slices, crushed and broken surface materials are also subject to erosion from other vehicles using the crossing, and possibly wind dispersement of the particles. I would suggest a surface treatment of the crossing which is resistant to deformation and a crossing that is well drained. The nature of the material could range from railroad ties to special crossing mats, to concrete slabs.

If you just have to produce a calculation, you might use the vehicle stresses due to normal vehicle traffic reduced by the ratio of 13/83. If you do that, then you should probably post a permanent crossing guard, or at least load limit signs. Its not gas, where the DF might change the wall thickness. And you know that a car or truck will eventually find its way out there and cross it, so why not just design a typical 4 ft clear depth for 83 psi wheel pressure and get on with the rest of the pipeline. That's what I would do.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

I'm with Mr 44 here. Tracked vehicles are usaully better as they don't have a point load, however they are pretty heavy and can easily chew the ground up, especially if it rains.

The key part is to ensure that the crossing point won't subside under the weight of lots of things crossing. If your pipe ends up trying to hold the road up you're in big trouble....

I would always put in at least one bog mat directly over the crossing and if anyone needs a calculation, try looking up "Spanglers" method.

The attached is pretty useful as a guide and reference.

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