Spiral Tunnels

From Academic Kids

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Power_exits_Lower_Spiral.jpg
CPR 5844 emerges from the lower spiral tunnel, passing under its own train, 1986. Photo by David R. Spencer

When the Spiral Tunnels of the Canadian Pacific Railway were opened to traffic in August, 1909, they were hailed as one of the engineering wonders of the day.

In 1884, when Canadian Pacific Railway construction crews first encountered the Kicking Horse Pass they found at the summit a staggering drop with no room in either Kicking Horse Canyon or the Yoho Valley to lengthen the line so as to reduce the gradients. To save time and money the tracks were laid in a steep descent from the top of the pass to Field, dropping 237.5 feet to the mile (4.5%).

Early railroaders named this hazardous stretch the Big Hill. They often worked in blizzards with temperatures dipping as low as -30C or -40C. There was the persistent danger of avalanches and rock slides as well as stalled engines and runaway trains.

By the early 1900s increased traffic over the line made it imperative that something be done about the bottleneck caused by the Big Hill. Engineers were faced with the problems of space due to the steep mountainsides on both sides of the divide. The problem was solved by creating two spiral tunnels into the two mountains to gain the track length needed to reduce the grade to an acceptable degree. John Edward Schwitzer, Senior Engineer Western Lines, Canadian Pacific Railway, was the designer.

The rail line, going west from Hector to Field, encounters first the Upper Tunnel, or No. 1, as the railroaders call it, which cuts 992 m (3255') into Cathedral Mountain, turning through an angle of 288 and passing under itself to emerge 15 m (48') lower. The track then snakes northeast, crossing the Kicking Horse River and enters the Lower Tunnel, or No. 2, in Mount Ogden. This tunnel is 891 m (2922') long with a curvature of 226, and emerges 15 m (50') below the entrance and continues westward. In this intricate system of spiraling track the trains run through the valley by three lines at different elevations and cross and re-cross the river by four bridges.

The monumental task entailed cutting through crystallized limestone of a widely distorted nature. Hardness and brittleness of the rock varied every few feet making drilling operations extremely difficult. These problems were aggravated by water seepage through the rock crevices which hampered progress on the downgrade ends of the tunnels and the high altitude (~1500 m or 5000') and severe winter weather that compounded the already adverse conditions under which the navvies worked. The contractor, MacDonnell and Gzowski, used at least two narrow gauge (3 foot) 2-6-0's on this work.

The result of the project was that the tunnels reduced the gradient of the track from as steep as 4.5% down to a maximum of 2.2%. The spiral configuration increased the length by 12.5 km (8 miles). With this improvement, two engines of the same class as the four previously required could haul even heavier loads over the pass by means of this Canadian engineering marvel.

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