The Confusion Hill project alleviates a recurring problem from the past decade of landslides and slipouts around Confusion Hill on Route 101. A large, ancient rock slide complex extends from the south fork of the Eel River to more than 1,000 ft. above, enveloping the current highway located 140 ft. above the river. This slide activity has caused numerous road closures and delays associated with one-way traffic control situations. Geotechnical studies of the site concluded that the ancient slide is progressively losing strength with a high probability that the slides within the complex will continue to move in the future. The current road had to endure numerous closures during the winters of 2005 and 2006 because of continued slide activity. Over a period of ten years, $33M has been spent on slide repairs.
This project replaces the existing highway with a 3-span variable depth cast-in-place segmental structure. The spans of the bridge are 106 m, 174 m, and 133 m with a bridge deck width of 13 m. The structure was built utilizing the balanced cantilever construction method with end spans constructed on falsework. The box depth varies from 3.5 m at the end spans to 9.6 m at the interior piers with a variable superelevation up to 11%.
FINLEY performed a time-dependent staged analysis of the structure to monitor stresses and anticipated deflections during construction. The analysis was further refined to accurately predict cantilever rotations associated with the deflections of the 51 m long integral columns. FINLEY provided construction and geometry control manuals and evaluated the geometry of each phase of activity during construction.