There are many ways to share surfaces between civil software packages. I prefer to use LandXML, but what if that isn't an option? What if the recipient wants the tin to be lines with 3d elevations?
If you export a Civil 3D surface to AutoCAD (or explode it twice), you are left with 3d faces. You can explode them as many times as you want, but you're still left with 3d faces.
Thanks to Google, I found the solution: Regions
In the AutoCAD drawing that contains the 3D faces, execute the region command and select the 3d faces. Now explode the regions that you created and you'll have lines with 3d elevations.
Yes, it's really that simple.
Thanks to Mike Perry for sharing his knowledge on the AUGI forums.