Depending on the subassemblies we use in Civil 3D, we may find it quite difficult when it comes to creating quick corridor surface Boundaries. For example, if we have varying subassemblies with varying codes for tie/daylighting slopes the “Boundaries > Add Automatically” function isn’t as useful as it sounds. We rarely get the results we want.
Try This Trick!
Trick Civil 3D into creating our boundary automatically. Some may already know this trick but for those that create single baseline corridors you most likely have never seen this. If a corridor has more than one baseline then when creating a corridor boundary, a new option for “Create Boundary from Corridor Extents” suddenly appears! I personally believe this should be included in a single baseline corridor. It is extremely useful.
Our Initial Corridor (Single Baseline)
The image above shows that there is only one baseline in our corridor. The image below shows the options we have for creatnig boundaries based off of the corridor design and the subassemblies used within it.
Temporary Additional Baseline
We can trick Civil 3D to automatically add the "extents" of our corridor surface as a boundary. The catch is that we must add at least one additional baseline to the corridor. The image below shows the addition of a baseline. The alignment and profile is not important because after the "extent" boundary is applied, we're going to remove the the temporary baseline anyway.
Notice the image below. After we applied the additional baseline, an option for "Corridor extents as outer boundary..." suddenly appears! To apply this as a boundary just select it. Then be sure to go back to the Parameters tab and remove the temporary baseline.
Select OK and the boundary will be applied as expected to your Corridor Surface.