How to employ the SurfaceExtractObjects tool to build a SHP file
Autodesk's Jerry Bartels walks through how to use the Civil 3D SurfaceExtractObjects tool and the MapExport command to build a SHP file of a surface.
From the Jerry's YouTube Channel.
and the Civil Imersion blog.
It probably needs to be said SurfaceExtractObjects creates the AutoCAD primitives on the Layers assigned by Civil 3D.
Most of the time you'll want to perform more object property adjustments to the primitives before you export them or
employ WBLOCK on the exported primitives and clean up first in a publish drawing. This typcially works much better in a real world project with more complex surfaces.