Avoiding Landslides

ASPIRE Magazine, Summer 2008, Segmental Engineer: Finley Engineering Group, Inc.

by Kevin Harper, California Department of Transportation

An emergency project to relocate a portion of the Pacific Coast Highway (U.S. Route 101) away from a large landslide in northern California required two large bridges to span the South Fork Eel River. Although the bridges are within a quarter mile of each other, they are dramatically different structures. The difference in the bridge types resulted from the vastly different terrains at the two crossings of the South Fork Eel River that snaked along in the shape of a giant “U” with a bridge over each leg. The southern leg of the river, with its wide banks, required a 1355-ft-long, three-span, segmental concrete bridge that was 275 ft above the river. The northern leg of the river, which passed through a narrow rock walled canyon, required a 581-ft-long, three-span, cast- on-falsework concrete arch bridge that sits 150 ft above the river.

Route 101 is the primary route that provides direct access to California’s north coast for commercial trucking and recreational traffic. North of the San Francisco Bay area, this highway is considered the “lifeline of the California’s north coast.” There has been a recurring problem of landslides around Confusion Hill over the last decade, resulting in frequent road closures and high maintenance costs. When a major landslide occurs that closes both lanes, the traffic south of Confusion Hill may have to backtrack and detour an additional distance of 250 miles. During the past 10 years, over $33 million has been spent on slide repairs. Read more…

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