I have a fairly large structure I am trying to model as sitting on sandy soil. I realize that to be really accurate I would need non-linear (sim pro only, dont have it) so I have been using a spring fixture to simulate sinking into it. This works generally well, but if a part is bending and lifting, the spring fixture resists motion away from it as well. What I would really like it a surface the model can push into (1 inch per 115PSI is the random number I am using), but can pull away without restraint. Short of modelling a large block of rubber (and trying to get the stiffness correct) is there any other approach I can take?