I often have question about modelling a tunnel.
You know that you can use templates and circles, but the 3D component is not using the true circle but stroking.The number of segment is defined using variable CIVIL_CIRCLE_MESH_STROKE_NUMBER (default 16 which is not that many).
So what about using MicroStation capabilities ?Here is what you can do; In the video I am using OpenRail Designer 2021 R2 (10.10.20.78).