Local Information

New construction method helps reopen SR 203 south of Duvall more quickly

Monday, August 31, 2020 - 06:55

Tom Pearce, communications, 206-492-9555

Fiberglass arches filled with concrete allow work to finish in just five weeks

DUVALL – A first-of-its-kind culvert has helped the Washington State Department of Transportation reopen State Route 203 just south of Duvall late Sunday, Aug. 30, much more quickly than traditional methods would have allowed.

The new culvert will allow coho salmon, steelhead and cutthroat trout to use an additional 3.5 miles of spawning and rearing habitat.

Contractors working for WSDOT installed the culvert – built with fiberglass arches that were filled with concrete – and finished rebuilding the highway over Loutsis Creek in five weeks. This is the first use of this system on the West Coast and for the agency, which helped shorten the time it usually takes to replace a culvert more than 40 feet under a highway.

“This approach requires less heavy equipment and can be done much more quickly than work that uses heavy concrete girders,” said WSDOT Project Engineer Shawn Wendt. “We have hundreds of culverts to replace in the next 10 years. This was a pilot project for WSDOT. We will evaluate it and determine if we may be able to use it for other projects.”

Finishing faster
Using traditional construction methods, it could take two to three months to dig up and replace a culvert 30 to 50 feet underneath a roadway. Working with the lighter fiberglass greatly reduces that time. A hollow 50-foot long, 1-foot diameter fiberglass tube only weighs about 500 pounds. That means a few people can move an arch and it takes only light equipment to place it, instead of the massive cranes a traditional concrete girder would require.

It took just six days to complete the bridge portion of the project, from pouring footings to curing the concrete inside the arches. The remainder of the project involved excavation and filling, temporary stream relocation and other concrete work.

Fiberglass arches
The fiberglass arches were built by AIT Bridges in Maine, then shipped to the Loutsis Creek site just south of Duvall. After crews from Goodfellow Brothers excavated about 19,000 cubic yards of material – more than 2,000 dump truck loads – from the site, the 12 arches were placed in less than a day, then filled with concrete. Plates placed across the arches completed the structure. After waiting a few days for the concrete to harden, the crews filled in dirt over and around the bridge, then repaved the road.

AIT Bridges and the University of Maine cooperated in the development of composite arches about 10 years ago. This type of structure has been used mostly on the East Coast since then.

SR 203 now a detour route
With the completion of the Loutsis Creek project, SR 203 is now a detour route for a King County project on West Snoqualmie Valley Road. Because that was the detour route for WSDOT’s SR 203 project, King County timed its month-long project until work on the highway at Loutsis Creek was finished.

People traveling on SR 203 near Duvall should plan for additional traffic during the West Snoqualmie Valley Road closure.

SR 203 slide area update

WSDOT’s geotech team is finishing a review of information gathered during a July site inspection of the slide area south of Kelly Road Northeast near Carnation. That information will be used to design a solution to mitigate the slide that caused a section of the road to sink several inches last winter and prevent future slides along this section of highway. Although there is no date for work, WSDOT’s goal is to start work by this fall.  

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