I read with interest about your tunnels. I haven’t laid any track yet but I did install 2 tunnels 14 inches in diameter under my water fall and under a set of steps. I think yours will work out well. What are you using under your track as a base? I have herd concrete with footings are the best so there is no heving from the winter thaw.(I live on long island)I did not put anything down yet and was thinking about crushed bluestone (like what would go down as a driveway) and tamping it. any suggestions. I am not new to model railroading but I am to garden railraoding.