BergerWorld: 2nd Quarter 2008

For nearly four decades, residents in Lexington, Washington, have awaited a new bridge to cross the Cowlitz River, giving them more convenient access to Interstate 5 (I-5). By 2000, Cowlitz County began working with state and federal representatives to obtain funding for the approved roadway and structure. Once funding was secured, B/A was selected to evaluate alternatives; prepare preliminary plans, specifications and cost estimates; and provide comprehensive construction administration services for the new $14.5 million Lexington Bridge.

The bridge approaches incorporate Mechanically Stabilized Earth (MSE) retaining walls and integrate a new roadway into an existing flood levee on the west side of the river. B/A designed the roadway and bridge slightly higher than the existing levee, with the bridge substructure serving as an integral part of the levee system.

Because the Cowlitz River, a tributary of the mighty Columbia River, is a migration route for salmon and steelhead and serves as an integral part of native eagle, songbird and elk ecosystems, environmental concerns were paramount during the construction. As a result, the Team adopted a very brief "in-water work window" that limited construction time in the water to nine weeks from July to September. The Team also utilized an innovative "bubble curtain" which surrounded piles while they were being installed to diffuse noise waves. As a result, no appreciable adverse impacts were detected on fish or other aquatic species. B/A also assisted in obtaining a number of regulatory approvals from local, state and federal permitting agencies.

The completed bridge accommodates approximately 11,000 vehicles per day. It also reduces drive time an estimated 20 minutes per trip and provides residents with a faster evacuation route during emergencies, such as serious winter flooding. The project was completed on budget and ahead of schedule.

B/A was also commissioned by the city of Kent, Washington, to serve as the lead design consultant and construction support for the Colonel Joe M. Jackson Bridge as part of the new South 228th Street extension connecting I-5 with Kent Valley. Prior to construction, Kent assured the Washington State Department of Fish and Wildlife that the bridge would be built over the Green River without construction equipment entering the water, thus protecting the fragile riparian ecosystem, a migratory route for salmon, as well as a habitat to a number of endangered species. In response, B/A utilized a transi-lift crane with a carrying load of more than 150 tons and a reach over 165 feet positioned on the river bank to place the main span and girders for the bridge, a process the Team accomplished in a single day. B/A also recommended that the spans be erected independently on simple supporters, with innovative "link slabs" that eliminated the need for expansion joints, minimizing the risk of potential damage in a seismic event in an area plagued by soft soils.

The three-span bridge was completed on schedule and under budget and represents an important milestone for the city of Kent, playing a major role in relieving traffic congestion and accommodating commuters traveling into the heart of Kent's industrial area.

The two-mile-long Tacoma Narrows Bridge links Tacoma with the Kitsap Peninsula. It is currently the fifth-longest suspension bridge in the United States. As part of a statewide bridge inspection program for the Washington State Department of Transportation, B/A, in cooperation with Associated Underwater Services, was retained to perform underwater inspections at the bridge. This was the first inspection of the Tacoma Narrows Bridge under the U.S. Federal Highway Administration's bridge inspection program. The program, which started several years ago as a result of a number of catastrophic bridge collapses caused by in-water foundation failures, requires the underwater portions of bridges to be inspected at no more than five-year intervals.

While typical underwater bridge inspections take place at depths of 60 to 70 feet, the Tacoma Narrows inspections required 160-feet-deep dives. In addition, currents in the Narrows are up to seven knots, notoriously swift and unpredictable, providing limited windows for diving. Prior to the inspections, the B/A dive team spent several months setting up the complicated dive, including 30 hours of training for each team member in a specialized surface recompression chamber that allows the divers to complete their decompression stops on the surface rather than underwater. The Team performed two dives per day for six days, resulting in the discovery of an unusually large scrape about 60 feet underwater. B/A theorized that the scrape was likely made by something hanging off of a vessel moored to the structure.