Sharu,

First, the theory and what software like Caesar can do is to count axial stress and strain. No buckling is considered. However, in reality, the pipeline in a soft soil can have a behaviour different than we assumed to be, because the energy necessary to buckle is less that the energy necessary to produce the counted stress-strain axially. But this is only an warning in our discussion.

In case you have a buried bend somewhere (as a part of a Z "offset"), let's say 300m from the pig trap, and VAL is 200 m, you may evaluate the possibility of that bend to move or not. I mean in this case it is not so important that the distance is greater than VAL, it is likely that in those 300 meters you haven't 100 m restrained because in the end of the segment with length of 300 m (where the bend is), soil cannot restrict axial movement by a force as calculated for a VA. However, in case you have a strong block at that bend (in practice, in our days- no, you haven't such block) you'll have indeed 100 m restrained there.

What I try to say is that you may apply such judgement case by case, looking to both ends of a straight segment of the pipeline and decide what is to be included in your model. And in case you decide to eliminate the middle part of a long straight segment, the problem of the "cap effect" (at truncating points of the model) is a supplementary issue that you need to solve, case by case.