AN UNIQUE TUNNEL

Back in the days of steam, Cascade Summit had a wye for turning helpers for their return trek down to Oakridge.  Fitting the wye into the geography at Cascade Summit, placed between Odell Lake and the summit of the Cascades, required a bit of creativity.  Specifically, the tail of the wye had to go back into the mountain.  This required a tunnel--a very unique one with only one portal! Adding to its unique nature was that the wye tail track tunnel was fully wood lined and had a wood portal.  All of the tunnels on the mainline above Oakridge had concrete portals and entry liners.  For reasons as yet unknown, the SP and its contractor chose to build the wye tail track tunnel using wood-only.  

The limited photos I have seen of the wye tunnel indicate it follows SP Standard Plans for a wood tunnel and portal.  Fortunately, the relevant plan sheet was reproduced in Volume One of the Southern Pacific Lines Common Standard Plans, published by Steam Age Equipment Company of Dunsmuir, CA, in 1992.  I adapted the SP C.S. 1750 plan to my model use with 36-inch radius curves leading to the wye switch.  I chose a portal width of 2.5-inches, which was the standard I used on my concrete portal masters.  This turns out to be quite close to dimensions specified in the plans for tight radius curves.  I drew my own tunnel profile plan and then built a simple assembly jig on that plan.

Armed with these standard plans, I built my model of the tunnel liner and tunnel portal using Evergreen styrene strip and scribed sheet.  I chose to build only the first (actual) foot of the tunnel liner to the SP plan and will line the rest of the tunnel with my usual foam core board liner used for previous tunnels.  

Tunnel plans, assembly jig and sections of portal.

The tunnel portal uses a simple post and crossbeam with diagonal corner braces matching the top corner bracing of the tunnel liner.  Another detail just showing in the plans in the photo is the diagonal braces for the front of the tunnel portal.  With additional side sheathing, these form wing walls for the tunnel portal.  

Once the portal pieces were built, I started building tunnel liner braces. The five pieces were fit around the assembly jig and glued.  I began liner construction by gluing scribed sheeting between end liner braces. Sides, top and top corner diagonal liner pieces were attached to form the basic structure.  Once this set, I began inserting liner braces at four-feet spacing.

Initial Liner construction.

Installing liner braces.  Wood clothespins make a great clamp for holding styrene joints for gluing.

Completed, but unpainted, tunnel liner in place around the summit wye. This unpainted view shows the diagonal front braces for the portal and the nut-bolt-washer detail applied to the specified joints.  The rear half of the tunnel liner will remain removable for maintenance access as will the yet-to-be-built foam core tunnel liner.

Completed tunnel portal and liner assembly.

As seen in the photos, the tunnel portal was located at the wye switch points.  The mountain geography forced a very tight installation.  Most steam helpers on the Cascade Line were cab-forward articulated locomotives.  Light helpers would be backed into the tunnel, keeping the crew close to the tunnel face and clear air.  In spite of that, there are tales of cab forward locos trying to lengthen the tunnel, usually as a result of a brake system failure.