Sometimes it’s necessary to convert a Civil 3D surface into a Revit surface.
The first thing is to change the drawing’s Proxygraphics setting to 1. This will save a copy of the linework that makes up the surface in the drawing. Make sure the major and minor contours are shown and they are on layers other than 0.
Next on the Insert Tab in Revit use the Link CAD to bring in the drawing that contains the Civil 3D Surface. Go to a 3D view and using the Massing & Site tab, use the Toposurface button to create a new surface. Then use the Create from Import >> Select Import Instance. Select the CAD drawing and only select the layers the contours are on.
Here’s the steps in video form: