OVERBURDEN COMPACTION MULTIPLIER

estimated

Someone can interpret like or which is the relation to obtain this information, since I relate it with proctor.

Thank you

Regards.

This is a "tweak factor". The "help text" suggests (8*Proctor_Number).

We've had a few users question the theoretical background on this Overburden Compaction Multiplier (OCM). This is a C2 term and does not have basis in theory.

We have it in C2 because it provides additional user adjustment to the transverse stiffness properties of the soil-pipe interaction. As Rich mentioned, we default to OCM=8 and that can be used with the ratio of the pre- & post-overburden densities. For example, if you put half the soil back on top of the pipe in the trench, then the ratio is 0.5 and you may want to use an OCM of 4. Again, this is an additional multiplier on transverse (not axial) stiffness values.

If you have your own soil stiffness and load limit values, you can enter them directly in the C2 soil modeler.

My experience and that of other C2 users I've discussed this with indicates that a OCM value of 5 or 6 typically provides more realistic stiffness values than the default of 8.

I would recommend that the C2 default value be changed to 5, as many users cross their fingers & hope that the default is appropriate.
That said, the user should have an idea of what soil stiffness is appropriate, and either use the OCM to acheive it, or enter their own stiffnesses as Dave suggests.
It is also wise to consider an envelope of possible stiffness values; such as +/- 20%.

There is a helpful guide available on the Internet that addresses soil stiffness and other pipeline design issues:
American Lifelines Alliance - Guidelines for the Design of Buried Steel Pipe.
http://www.americanlifelinesalliance.org/pdf/Update061305.pdf

J.