How do I tie-in a Civil 3D dwg to a 3D (CAD) but non Civil 3D dwg?

[CaddyMcCadface]

I have a contour file, and a corridor of the same area of motorway (carriageway). I have received 3D information in CAD format (non Civil 3D format) and I now need to raise one channel up to tie into these new levels.
What would be the best way of doing this - amending a previously created Corridor, creating a surface on the Contours dwg or doing it all from scratch?

Civil 3D newbie, so be gentle.

Cheers

[Domziman]

First thing that you would have to do is create a Surface from those CAD format entities, I hope that you have received it in a proper format like 3D lines or normal lines with elevations for example. From there you can simply create your assembly you need and create the new channel when it is suppose to be.