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Oneonta Tunnel Rehabilitation

Oneonta Tunnel Rehabilitation
Columbia River Gorge, Oregon

This 125-ft-long roadway tunnel was constructed in 1914 and is part of the Historic Columbia River Highway. The site is located about 2 miles east of Multnomah Falls. By 1948, the passage was too small for modern cars and trucks, and the highway had been rerouted, so the old tunnel was abandoned and plugged with debris. In 2006, the historic tunnel was rehabilitated for pedestrian use. Geotechnical considerations included the stability of massive rock cliffs above both tunnel portals and the condition of the rock walls and roof of the abandoned tunnel. Additionally, the engineered tunnel support system had to be hidden behind the re-constructed wooden tunnel lining and stone masonry portals. GRI conducted a geologic reconnaissance of the site, provided preliminary recommendations for tunnel support for use in estimating a construction budget, and evaluated rockfall hazards at the tunnel portals and nearby parking areas. GRI prepared final plans, specifications, and a cost estimate for the Western Federal Lands Highway Division of the FHWA and Oregon Department of Transportation to be used in bidding and construction of this project. Patterned rock bolts in the roof and shotcrete lining reinforced with welded wire mesh and steel fiber were used for tunnel support. Horizontal rock dowels 20-ft-long were constructed in the cliff face above the west portal to provide support for rock with prominent fractures exposed in the cliff face. Mine straps were used for additional support in areas with closely spaced fractures, and steel sets were constructed to support a zone of severely weathered rock near the east portal. GRI provided engineering, engineering geology, and inspection services during construction.

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