Multnomah West Viaduct

"...viaducts resting on unequal length columns and anchored to the slopes [half-viaducts]. A good example of this occurs on the Historic Columbia River Highway west of Multnomah Falls. Even though this project was carefully undertaken, heavy storms in 1921 forced the highway department to further stabilize the viaduct by adding concrete support walls behinds every other column."

Samuel C. Lancaster, The Columbia River Highway In Multnomah County

Just west of Multnomah Falls this steep slope extended down to the very edge of the rails of the O.-W. R. & N. Co. How to get by this place was quite a problem, as the steep slopes were made up of loose rock and earth which had been detached from the cliffs above in past ages, and now held by the heavy growth of underbrush and timber which caught it, the whole mass being tied together with their roots.

To cut away the toe of the mountain sufficient to get width for the road, or even to attempt the construction of retaining walls, meant disaster, for the whole mountain, for hundreds of feet above, would then slide down.

Accurate maps and cross-sections showed that a reinforced concrete viaduct 400 feet in length would serve the purpose best. The height of the viaduct being fixed by the slope of the mountain and its relation to the railway tracks, one side of the concrete floor slab of the viaduct rests on a 16-inch square reinforced concrete column, the core of which is hooped with steel. These columns are spaced 20 feet apart, parallel with the railway and 12 feet from the center of the track. They are 10 to 20 feet in height, according to location. The other side of the concrete slab rests on a substantial footing, dug into the steep slope above, the foot of the lower column being connected with the upper footing by a diagonal strut 16" x 16" of reinforced concrete, insuring stability.

We believe this to be an original type of construction; it is economical and pleasing in appearance, and does the particular thing for which it was designed.

Robert W. Hadlow, Columbia River Highway Historic District, National Historic Landmark Nomination

CS12. Structure: West Multnomah Falls Viaduct, No. 840 HAER No. OR-36-G

Location: HMP 31.9

Date: 1914

Designer: K. P. Billner, Oregon State Highway Dept.

Builder: Pacific Bridge Company, Portland

Owner: Oregon Department of Transportation

This 400-foot viaduct consists of twenty 20-foot reinforced-concrete slab spans. Two parallel rows of 16-foot square columns, 17'-6" apart, support the deck. Roadway width is about 18 feet.

The structure was designed to ride along the hillside above the railroad mainline because of tight right-of-way clearances. A concrete retaining wall runs along its south elevation. The arched railings were constructed of plaster concrete and metal lath. They represent a member of the family of bridge railing designs found on the CRH.

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