I'm doing some FEA on a corrugated sheet metal tunnel that will be installed as a 5 m diameter reclaim tunnel under an ore stock pile. Think of it as a big round pipe buried under dirt. There is a rectangular cut out in the top but that is irrelevant to this question.

Not sure how to restrain the model. An elastic support with the appropriate stiffness of soil and a normal pressure to represent compaction of the soil around the tunnel is my current thinking. Question is when doing an elastic support, does it represents a stiffness in both directions. That would be true for most materials. Dirt is a bit different. It will compress with a certain stiffness but it won't spring back the other way with the same stiffness. Any thoughts.