To build my tunnels, I first had to dig out the slope. Once I had a base which was either level or at the appropriate grade, I then started on the walls of the tunnel.

The tunnel walls were built up using concrete bricks or blocks, depending on how much space was available. The blocks were glued together with urethane glue. This has proved to be sufficient. You could also use a heavy duty construction adhesive.

The interior walls of the tunnel near the ends were textured to simulate the look of stone. I did this by spreading tinted mortar onto crumpled aluminum foil which had been sprayed with Pam. This prevents the mortar from sticking to the foil. Then the foil and wet mortar are pressed against the tunnel wall. After the mortar hardens the aluminum foil is peeled off, revealing a rocky texture.

Farther in, the tunnel is simply painted flat black. This is fine for most purposes, as the interior is not visible from outside. However, I found that it shows when recording video with a camera mounted on the train. In January 2011 I began adding more stone-like texture to the tunnel interiors, wherever possible. In retrospect, I wish I had completely lined all the tunnels with texture during construction.

Reinforced concrete slabs were cast to cover the top of the tunnel. I used 6” x 16” x 2” concrete capstones to make simple forms on the floor of my garage. I then covered the form with a large plastic trash bag. Hardware cloth was cut to fit into the form -- usually two layers of it. I also added 2-3 short pieces of 3/8” steel rebar. High strength concrete was then poured into the form. After it sets, just move aside the capstones from around it, and lift out the slab. Be sure not to make the slabs too big or you won’t be able to lift them!

My longer tunnels have access panels which double as steps on the upper level pathway. These were originally concrete slabs, constructed as described above, with steel eye bolts set into them. The eye of the bolt is recessed into the upper surface of the slab. I used hooks to lift out the slabs when necessary.

These concrete slabs proved to be too heavy for frequent removal, so in 2010 I began replacing them with wooden panels made from pressure-treated 2x8 boards. Small brass hinges are used to as “handles” -- when not in use, they fold flat.

The panels are then covered with a rubberized mat to reduce the amount of rain that drips into the tunnels. It also looks better this way.

Below is a view into one of the tunnels at the west end, with the access panel removed. This access is built into the stairs.

Updated April 28, 2011

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