AutoCAD Civil 3D

[#1]

Creat another surface "Void-1". Paste the non-roadway surface into it. Add a boundary that matches the void area inside the roadway. Paste the three surfaces into your combined surface in this order: "Non-roadway surface", "roadway surface", "Void-1 surface".

[#2]

this is the approach I'd take although just check that the triangles form correctly at all common boundaries. They usually do but occasionally you might have a gap which can be closed by adding a show boundary.