compression-only solid elements?

[Sostratus]

I'm investigating a tunnel which will be subjected to loading from the street level. I have created a SAP2000 V14 model using solid elements. The concrete tunnel walls are surrounded by rock which will not be able to transmit tension. For other projects I have run nonlinear analyses and used compression and tension limits for frame elements, but I do not know how to apply tension/compression limits to solid elements.

What is the best way to ensure that the 'rock' solid elements are compression only? Thanks!

 

[stressed]

Select solids, then Assign>Solid>Surface spring and select compression only option when assigning a K value stiffness for the rocks. You'll have to run your load cases nonlinear