The scenario is within Autodesk Civil 3D when creating a composite surface by pasting EG (existing grade) and FG (finished grade) together. The expected/desired result is the Road FG with a clean tie to FG.
This is seen only when a completely enclosed corridor is created, like in a Subdivision Layout, Pond, enclosed Berm, Etc… Instead of a clean paste, as expected with a continuous contour, you’ll get
1.) A void or a hole in the enclosed area.
2.) Straight triangulation across the gap, flattening out the EG conditions.
Both conditions may result in incorrect Contours and Earthwork Quantities.
To create a singular boundary that encloses the entire corridor design with ONE (1) single Polyline. You need to play with where to cross in between corridor samples to loop in the void areas and wrap around the outer perimeter.
Once that singular continuous boundary is created and assigned to the Corridor Surface, the Composite Surface will build appropriately.
I hope this clears up any issues you may have seen in the past when building corridors and composite surfaces.
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