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My sample lines are not gathering any data ie, in the sample line properties under (sections) the offsets and elevations have no information in them. I'm using Civil3D,2012
Go to Sample Line Goup Properties "Sections" Tab, choose Sample More Sources radio button to sample data if not appearing on left under "Sections List".
If you have other sources available in other dwg's such as Corridor FG surface, Corridor Datum surface etc. Data reference them into this dwg using Data Shortcuts. Attach the corridor as an Xref
Then Sample those sources.
Hope this helps.