Thanks for posting those sketches @sanetdikkumbura1950. I would complete that last portion of your corridor in this way:
1. Split your corridor and create 2 regions and two different subassemblies for that (this may vary depending on the geometry of the ditch)

Notes:
for the first region use LinkOffsetAndSlope subassembly, so you can assign the slope value and have the surface boundary as your offset target.

The second region is the most complex because you'll have to deal with the body of the ditch which is comprised of several links. My advice is that you firstly see how the interact with the surface boundary when crossing it, and depending on that, create other regions that comply with the needs. (Use generic subassemblies for this)

For the last region you might want to use feature lines instead of corridors, use the corridor end points to tie in and create the last part of your geometry manually.
Best regards!
Camilo Fernández
Civil engineer | Specialist in design, construction, and maintenance of roadways
