The “Parallel Thimble Shoal Tunnel Project” is set to add a new tube and was scheduled to be complete in two years, but there’s a delay in the project.
I would have figured they would have constructed the new tunnel the same way they did the original. build new islands off to the side in line with the new bridges and prefab the tunnel sections, float them in and sink them in place. the islands would be away from the original tunnels so no chance of damaging them.