This combines the selected Existing surface with the "proposed" design surface created by Level AI. This provides a surface that can be used with InfoDrainage.

When Level AI runs it produces a raster overlay of the cut/fill surface, this is the cut/fill surface generated during the Level AI run.

You can generate a Civil 3D cut/fill surface by running this tool. This creates a surface that is the difference between the selected Existing surface and the "proposed" design surface created by Level AI.