I-90 Snoqualmie Pass East
Building a safer, more efficient, and reliable interstate
Snoqualmie Pass, Washington
Washington State Department of Transportation
Roadways & Bridges
The Washington State Department of Transportation awarded Atkinson a contract to widen I-90 from two to three lanes in each direction and improve three miles of roadway geometrics through several curves at the 3,022 foot summit of Snoqualmie Pass through the Cascade Mountain range east of Seattle.
Atkinson's Cost Reduction Incentive Proposal (CRIP) substituted elevated side-by-side viaducts for the contract snowshed. The twin 1,200-ft-long bridges rise over the avalanche chutes, can accommodate 100-year avalanche events, and virtually eliminate road closures due to avalanches. This approach also eliminates $37M in long-term operations and maintenance costs associated with the showshed.
The scope of work also includes 400,000 cubic yards of drill and blast rock excavation of the hillside, numerous large retaining walls, 116,000 tons of base course, 31,000 cubic yards of Portland cement concrete pavement, 38,000 tons of hot mix asphalt, 4,600 LF of drainage, and four new single-span bridges that replace existing culverts and improve drainage and wildlife and fish passage.
The project originally included an 1,100 foot long bridge over the lakeshore, however due to soil conditions, this bridge posed numerous constructability challenges and the associated Wall 7 was not constructible as originally designed. As a change order from WSDOT (known as the Wall 7 Redesign), the Atkinson/Jacobs team performed an alternative analysis and proposed multiple design solutions. WSDOT chose a new roadway geometric solution that eliminated the bridge and added two short retaining walls. The Atkinson/Jacobs team re-designed the area and re-issued the bid plans with extensive coordination with WSDOT.
Atkinson Underground performed rock bolting operations for the project.
Construction began in September 2011 and completion is scheduled for September 2018.
Atkinson has proposed a new solution to the avalanche area, and that is to replace the snowshed with a bridge type structure. This will allow the avalanches to go underneath the highway instead of over the highway like we had planned.
Brian White, Engineer, Washington State Department of Transportation