County adds bridge to coast project

MAPLETON Lane County engineers have had to shift gears in their effort to stabilize a remote Coast Range road after discovering unexpected conditions underground.

As a result, a bridge will have to be built over a shifting slope along Sweet Creek Road instead of holding the slope back with a retaining wall, as originally planned. Building the 1,130-foot bridge will add about $500,000 to the cost of the project, which will have to come out of the Lane County road fund.

The change will bring the total project cost to $6.3 million, project manager David Brown said. More than 90 percent of the projects cost is being paid through a federal grant.

The county is working to shore up a short stretch of Sweet Creek Road about 2 miles southwest of Mapleton, where an old retaining wall built in the 1970s is failing. Work began this summer on a 370-yard replacement wall, which has forced a number of nighttime closures on the road.

Sweet Creek Road provides access to 68 homes and about 30,000 acres of national forest land and more private timberland. About 5 million board feet of timber is harvested each year from forests served by the road, the county said.

Brown said initial engineering studies indicated that bedrock lay under a relatively shallow layer of soil, making a retaining wall the least expensive fix. But when excavation began, crews discovered that the bedrock layer was substantially deeper than the initial study estimated.

When you open up the ground, thats not an unusual condition, Brown said.

Nevertheless, county engineers were a little surprised, Brown said. They worked with a local firm, OBEC Consulting Engineers, to analyze the situation. It determined that crews would have to build the bridge over the soft ground rather than try to hold it back.

Brown said a bridge initially was considered the best solution, but that the county went with the retaining wall because it was less expensive. Work is now shifting to construction of the concrete piers that will support the bridge.

The bridge itself will be made from precast concrete that will be manufactured in sections and then trucked to the site and set in place. Once complete, any landslides or other earth movement simply would run under the bridge.

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County adds bridge to coast project