How to build tunnel liners: Concrete and rock

Spoiler for the next big post: I’ve been adding a lot of scenery base in. I decided to make my life MUCH easier and put in my tunnels, weathering and all, before the hills above, and I’m very happy with this strategy!

The prototype Paulson tunnel is 365 feet long through a nose of rock that shuts McRae Creek into a tight canyon known as Paulson Gap. This is one of my favorite spots on the Boundary subdivision, as it contains sheer rock faces, a tunnel and a snowshed in a few hundred feet of track.

The tunnel itself has poured concrete portals dating back to the 1940s. These continue about 30 feet back into the tunnel or so, where it reverts to blasted rock.

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For the portals themselves, I used Chooch concrete portals with the top trim cut off and the corners rounded to mimic CP’s very utilitarian method.

Here’s where I got clever.

I made a form to act like the wooden forms the concrete would have been poured into. This form was made out of a dollar store ‘for sale’ sign with lines scribed into it with a somewhat dull exacto blade and a ruler at (roughly) the same points they are on the portal. Then, using a hot glue gun, I temporarily attached this form to the inside of the two tunnel portals. This ensured that it kept its shape, although the tunnel is much longer than that!

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I had some clearance issues, the tunnel being on a curve combined with the narrow portals caused a slight rub from my test autorack. In the end, I changed the shape of the liner from a rectangle to a parallelogram so that the end away from the portal was higher. This solved the clearance issue.

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With the form ready, I soaked some paper towels in a slightly runny plaster of paris mix (since they don’t carry hydrocal within 500 miles of me anymore) and draped them over the form, making sure the plaster was worked into every nook and cranny – though the end result says I could have done a better job!

Removing the form yielded a look that was almost perfect. The transition from portal to liner could be a bit smoother, but I ended up filling the gaps with more plaster. Then I painted it with a mix of mostly unbleached titanium and raw umber, following it up with washes of both unbleached titanium and black. (Couldn’t find the india ink)

Here’s two photos before the patching and final wash:

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Next, I was going to just use black construction paper for the rest, but as I was putting it on I noticed that you could tell by looking through the tunnel as it was short enough that you could barely see the other side! The prototype is quite a bit longer, after all…I was all ready to start carving some plaster and was talking to my dad about how he did his tunnel liners with crumpled aluminum foil molds when he said “Why not just use the foil?”
Freaking. Genius.

This was seriously SO EASY. Crumpled a sheet of foil, spray painted it with some matte oxide red I had lying around, shaped it, stapled and hot glued it onto the existing liners (which were glued down by this point) and voila! It looks SO much better. It’s hard to show in photos, especially since I can’t get a tripod in. It’s only on the outside of the curve, since you can’t see the inside from any reasonable angle. There’s construction paper over the top to prevent light entry, and it’s attached with push pins to allow easy access in case of a derailed car.

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Seeing the light shining through from the other side is nearly unreal in how good it looks.

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Can’t wait to get that hillside built over it!

 

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Until next time, highball!

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