Doesn't matter, the philosophy is same as for "unrestrained" buried pipe as per B31.8 or B31.4 Codes. Liberal stress is a valid option, but 1.25*(Sh+Sc) limit cannot be practically used, because of longitudinal pressure stress.

Actually, ASME B31.3 with 2012 Ed. updates represents a very good option for buried pipe analysis, assuming the pipe-soil interaction is modeled properly.

Regards,