C3D Surfaces to 3D solids

[valejandro_ibarra]

is there a way to convert terrain surfaces in civil 3d to autocad 3d solids?

[andrewp.148283]

You can extract the the triangles out as faces using extract objects from surface command, which you can turn into solids, just can't remember how at the moment.

[brian.hailey933139]

After extracting the triangles, you can run the following lisp routine. I'm linking to the Autodesk discussion forums where the author posted it. I think that's the fairest way to do it.
http://discussion.autodesk.com/forums/thread.jspa?messageID=5305011