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I have three tunnels that are a total of 90 feet in length on my RR and have been using them for five years. Two are 35 feet long and about 2-1/2 feet deep, and one is a half circle with 4 foot radius, and about 4-1/2 feet deep. Yes, I disagreed with all the experts and built them anyway, and I have no regrets. But they were a lot of work. I had help the help for a contractor to build them. (We removed 2 dumpsters of dirt from our berm). My method was to build the walls out of 4" thick concrete block placed like brick. Under the bottom row we put a bed of 3/8" rebar. We then built them to within six inches of the surface of the ground. To make them super strong and last forever, we filled the hollow core of the concrete blocks with mortar mix after we stuffed rebar pieces we cut to size. The sides are very strong! The top was also made of concrete block which were cut lengthwise like pieces of pie to follow the tunnel on curves. Straight sections required no cutting. The sides of the tunnel were spaced to exactly fit these concrete blocks which are standard size. These were then filled with mortar mix to make them stronger as well (and heavier). They are then fitted onto the top of the tunnel like a jigsaw puzzle leaving only narrow cracks between the blocks. Over this I put pool liner material I had left over from the water feature and there has been no mosture in the tunnels. I cut the rubber pieces in three foot lengths, and the overhang the tunnel top by about six inches on either side. Bark dust about three inches thick completes the tunnels and makes it look like there is no tunnel there at all. They are true tunnels boring through mountains. To access the tunnel, simply push aside the bark dust, pull off the three foot long rubber liner, and remove the concrete blocks that rest on the top of the tunnel. They are loose (just setting there, so it is pretty easy. The 4-1/2 foot deep tunnel is another matter. For that one, I had to build access holes into the side of the tunnel lining I can climb into and reach anything that goes off the track. I build plywood access hatches to fit over the top of the concrete block walls. The plywood is fiberglasses to protect for the rain we have in Oregon. The roadbed is made of concrete as well with pressure treated 2x4 spaces in 6" lengths placed crossways (same direction as the roof). I used 10 foot long bender board to create the sides, and filled with mortar mix troweling the surface flat. The LGB flex track is nailed with brads to the 2x4" to keep it in position. Don't forget to use rail clamps, solder the rail joints, or put jumper wires around all the rail joints. Using five foot long flex rail keeps joints to a minimum. Graphite paste is also an option, but I prefer soldering with a torch, pulling the ties back to protect from melting. Finally, you must protect your tunnels from critters. I built wood tunnel portals, and then wood inserts with handles that exactly fit the opening. They are always in place when I am not operating, and no one has made a home in them yet. I used plywood pieces until the tunnel portals were finished. If you run with track power as I do, you will need the LGB track cleaning engine to clean the track in the tunnel. This cleans the track in front of the engine, and works very well. I try to never push cars through the tunnel, although I have done it with a video camera. After the winter, I run it through three times before sending in normal engines. I run only reliable equipment with metal wheels on the layout. I have had to pull off the top of each tunnel once or twice in the last five years, and it takes only about five minutes to reach a train, provided you can find it, but about a half hour to put it back properly. I usually send a loco in after one that is stuck to nudge it, and it usually works. I have also had to climb into the manholes (about 3x3x5 in size) a few times to make repairs or retrieve a car. The rocks on top of the manhole cover can be removed in five minutes and you can climb in. I could put the top on when I am inside, and no one would know I was there. The roadbed and track were installed before any of the tunnel walls were begun as you need shoulder width to be comfortable installing the roadbed and track. As I said, I broke all the rules, but created a railroad with tunnels that visitors actually wonder where they come out. Good luck on your project, and don't be afraid to try it. But be prepared for some work and some expense if you try my methods. Bill Derville
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