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February 6, 2023
Jacobs Engineering Group
Project: West Sammamish River Bridge replacement
Client: City of Kenmore
The city of Kenmore knew replacing the West Sammamish River Bridge would be challenging. The old concrete bridge dating to the 1930s was structurally vulnerable. The busy bridge carries more than 20,000 travelers daily, and construction would require lengthy traffic closures in a significant corridor to access Kenmore and the highly traveled state Route 522.
The Jacobs team investigated bridge scour conditions around the in-water piers, assessed geotechnical conditions, and conducted a bridge load rating analysis to determine the bridge’s load-carrying capacity. The team then evaluated bridge rehabilitation versus replacement alternatives and decided that replacing the bridge was the best option. The team worked with the city to obtain approximately $35 million through various funding sources.
Priorities for the new bridge included improving safety and mobility for all modes of transportation. The new bridge design consists of a wide multiuse, non-motorized path with an architectural railing, an aesthetic finish on the concrete barriers, LED lighting enhancements, and an overlook bench featuring historical oars and interpretive signs. The design also provided a gathering place in the middle of the bridge, where pedestrians can pause to enjoy views of Lake Washington.
The construction of a new bridge would need to consider many complex elements. The design needed to achieve the city’s objectives for the project while also safely maintaining mobility through the corridor during construction.
The Jacobs team evaluated many options to determine the best solution featuring a five-span, 600-foot-long bridge with precast concrete tub-shape girders supported on 8-foot-diameter drilled shafts driven a maximum of 90 feet into the existing ground. Construction started in January 2020 but soon faced a supply-chain shutdown and delay due to the COVID-19 pandemic. However, the team and the city worked together to make up time and keep the project on schedule.
During preliminary design, Jacobs developed detailed construction impacts documents, and scheduled to accommodate limitations on construction staging duration, including a short in-water work window and space constraints due to the existing northbound bridge’s proximity to the replacement bridge.
A highly visible project, the West Sammamish River Bridge included restricting traffic during the summertime when this corridor experiences heavy use due to the nearby golf course, boat launch, and proximity to parks and Lake Washington. The Jacobs team worked with the city to provide community outreach as the project progressed.
The new bridge will serve a variety of travelers for decades to come as a result of a collaboration that enabled the team to provide an updated transportation solution to serve the community.