So, at some point in your Civil 3D career, you may find yourself needing to combine a design surface that loops around and has a hole in the middle with an overall existing surface. No problem you may say to yourself. You know better than pasting your design surface into your existing ground surface so you create a new surface (I’ll call it Final Site Grading) and paste in the existing ground and then paste in the proposed ground. You take a look at your final output and, what on earth is going on? Well, when you paste a surface that has a hide boundary (necessary in order to create a void in the middle), the paste doesn’t recognize that hole and simply fills in the middle or, doesn’t fill anything in at all. What to do?
Well, here’s my solution. I’m sure there are other solutions out there but this is what I’ve come up with. Create a third surface that will just show the interior portion of the existing ground surface. Again, we all know better than to copy the existing surface, I mean what happens if the surveyor decides to make some changes? Create a blank surface and paste in the existing ground. Extract the interior boundary for the design surface, and then add that to the interior surface as an outer boundary. Now, when it’s time to make the Final Site Grading surface, paste in the overall existing ground surface, the design surface, and then the interior surface. Remember, these surfaces can come through via datashortcuts too!