This question comes up a lot
How do I build a trench or ditch model where for example I want to have the ditch bottom connect to a rock surface at e.g. 1:10 and then have a rock bench for e.g. 10’ that follows the rock surface followed by a tie slope out to existing at e.g. 3:1
You can use both the corridor model and the sideslope commands to create this type of feature as follows
- Create an offset slope instruction for the ditch bottom right (DBR) at e.g. 5’ offset at -5%
- Create a surface tie instruction to Rock from the DBR at the 1:10 slope (Rock Tie R) - ignore the ditch width and fill slope by leaving them blank.
- Here is the trick - create a dummy point not in the finish grade or any other material layer at an offset of 10’ and at 0 elevation delta
- Now create a surface instruction and limit the lateral extents of the instruction using the node to node method for both left and right edges of the rock bench i.e. the Left offset is from the alignment to Rock Tie Right and the Right offset is from the alignment to the dummy point (when defining the right side of the trench) and use the rock surface as your reference
- Now create the tie slope out to existing using a side slope instruction at 3:1 for Cut (and ignore the ditch width and fill slope by leaving them blank).
Video shows you how