Flexible steel pipe on embankment

[SMiK21]

Hi all,

I have a question regarding a steel pipe which will be buried in an embankment. Using the Marston-Spangler theory, the dead load on top of the pipe will be the full amount of the soil prism above the pipe, I get that.

My question lies with the way to determine the pipe's deflection: is the Iowa formula valid for both trench and embankment conditions? It takes into account the modulus of soil reaction E' which depends (refering to table 6-1 of AWWA M11) on the depth of cover, type of soil and relative compaction of the fill soil.

Intuitively, I am inclined to think that the passive resistance of the lateral soil would be greater in a ditch rather than in an embankment - the soil adjacent to the ditch is much more consolidated than the soil of a new (though compacted) embankment, so it will offer better lateral support.

Any thoughts? Thank you!

 

[BigInch]

If the pipe is parallel to the run of the embankment, you will have different loads on each side, one greater than the other due to the greater overburden on that side. If the overburden is significant, find a different formula.

Since the trench is overexcavated at least 12" in width to each side of the pipe, the sides of the trench itself do not contribute to the system. Compaction of the backfill into the space between the pipe and the side wall is what provides lateral stability, and that is approximately equal in both types of trenches.

you must get smarter than the software you're using.

 

[SMiK21]

Thank you for your reply, but I don't quite follow you.

What I meant was that I have an installation similar to the picture on the right side of the attached file as opposed to the left side. I don't understand how I will have different loads on each side if the embankment covers all of the pipe in the same way on both sides.

Compaction of the backfill into the space between the pipe and the side wall is what provides lateral stability, and that is approximately equal in both types of trenches.

Even if the side wall is significantly away from the pipe (say, 10 or 12 m)? A proper soil compaction won't be a problem.

 

[BigInch]

OK. You should have included the drawing to begin with.
All the soil in the trench in the left diagram needs to be compacted.

You're right, there are different factors for burying in fill, as the side support is markedly weaker. There is a Corps of Engineers publication that addresses those two conditions and combinations thereof,

http://www.publications.usace.army....YUDKmgqMrw=&tabid=16439&portalid=76&mid=43544

you must get smarter than the software you're using.