Trim Particular Elements: Manual Trim

only that part of the tunnel-shaped Shell that is inside the V-shell should remain; and
2.
From the context menu, choose Connect > Trim Elements to Roof/Shell.
Note that the cursor has changed to a little roof. Use it to click the element to use as the trimming element (here, the V-shaped shell, with red feedback).
Note: If Trimming Bodies are not on, they will appear here automatically for the duration of the trimming operation.
4.
Now you must select the part of the tunnel that you want to retain. Move the cursor over the parts of the tunnel (inside and outside of the V-shell) and see how the blue feedback identifies them: this indicates the options for which parts of the tunnel can be retained after the trim:
5.
You want to retain the part that is inside, so click on that part. The trim is executed.
Note: Alternatively, Ctrl-click one of the parts to eliminate it. The feedback will always show in blue the part that will be retained.
2.
From the context menu, choose Connect > Trim Elements to Roof/Shell.