Wilder Projects

High Bridge #41

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Project Location: Snohomish, Washington

Client: Snohomish County Public Works

Construction Cost:
$2.9 million

Wilder’s Role: Prime

Construction Period: 9/95 – 12/96

Project Highlights
50,000 CY approach fill 425 foot long new bridge construction Post tensioned concrete box girder Stringent environment controls 180-FT steel/wood work trestle Built by Wilder's Civil Construction Division and Snohomish County Branch Awarded 1997 Washington Aggregate & Concrete Association Excellence In Concrete Construction Award (Public Works Category)

This three-span post-tensioned concrete box girder bridge, 425 feet in length, was built for Snohomish County Public Works. The design included two 11-foot lanes with 6-foot shoulders over the Snoqualmie River to connect the growing rural population to Monroe by replacing a twenty-foot wide steel truss span built in 1924.

An elevation of 55 feet places the bridge deck 8 feet above 100-year flood projection. 30,000 tons of fill on the Crescent Lake Road approach was required to reach elevation before major construction could commence. Major flooding twice forced the work crews to relocate to higher ground during construction.

The confined area between the old bridge and the new structure allowed barely enough room to construct a 180-foot long steel/wood work trestle. Constructed on 26-inch diameter by 3/8-inch thick sheet pile driven to 115-ton bearing, the trestle provided access for Wilder’s 150-ton Lima crawler crane, which provided all the required hoisting for the new structure and assisted in removal of the existing bridge.

Varying heights, sloping walls, and the large overhangs required constant verification of dimension for the parabolic design. The arc of the underside of the bridge was built to provide a pleasing look to the public and more clearance at the mid section for potential flood danger. The 425-foot length of the deck was poured in three sections.

The two main piers, 235 feet apart, were placed on each bank of the river to keep the water flowing free of any obstructions due to floating debris. The resulting design required an extra high strength (7,500 PSI) concrete.

Four specially designed disc bearings and fabric pad slide bearings each support 1,000 ton loads and provide a slide surface to move six inches in any direction as the concrete might expand or constrict due to temperature changes.

Post tensioning keeps the span from sagging by providing a counteracting force to the bridge and traffic weight. A special tubular steel handrail/guardrail combination runs the length of the new structure.