Hello,

Another thought regarding modeling technique. It may be of interest to you to look at B31.1, Power Piping, Appendix VII, "Nonmandatory procedures for the Design of Restrained Underground Piping". The referenced Appendix will provide some guidance for one possible modeling technique that the analyst might consider using in an analysis model.

The design and analysis of the piping system is the responsibility of the engineer. The engineer must be satisfied that the analysis satisfies the intent of the applicable Code. If the engineer can agree that the boundary conditions described in the cited Appendix are appropriate, the technique can be employed in the model and the B31.8 "Code checker" can be invoked for the stress checking.

Just my opinion.

Regards, John.