Project news

• Snoqualmie Valley Trail users should be prepared for construction work along the trail under I-90 near North Bend. To see what you can expect, maps are posted here.
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Overview

Beginning in spring 2020, contractor crews working for the Washington State Department of Transportation will seismically retrofit six bridges on I-90 between East Sunset Way/Highlands Drive Northeast in Issaquah and 436th Avenue Southeast in North Bend.

What is seismic retrofitting?

Seismic retrofitting reduces the risk of bridge failure during earthquakes. The retrofit includes putting steel jackets around the columns from the footing at the bottom, all the way up to the underside of the bridge deck. After the jacket is installed, grout is pumped into the gap between the existing column and the new steel jacket. This prevents the column from buckling during a seismic event. In some cases, the bridge cross beams will be bolstered. This process involves making the beams stronger by making them bigger.

What drivers can expect

Most travelers won’t notice any changes to the bridge because it is all happening under the deck, and on the columns below the bridge. The highway will not be closed during this process, but there may be single lane reductions on the local streets nearby. Those reductions will be updated on the King County construction page as the project progresses.

Needs & Benefits

• Safety: Ensuring that the bridges are seismically retrofitted reduces the risk of the overpasses cracking or collapsing during an earthquake.
• Preservation: Retrofitting helps reduce potential damage to the bridges in the event of an earthquake by strengthening the columns and crossbeams that support the bridged sections.
• Economic: Seismically retrofitting the bridges helps reduce the risk that travelers and commerce will be disrupted after an earthquake.

Timeline

• January 2020: Project advertised for competitive bidding.
• February 2020: Project scheduled to be awarded.
• Spring 2020: Construction scheduled to begin.
• Winter 2021: Construction scheduled to be complete.