Project DetailsLocation: Snoqualmie Pass, Washington
Owner: Washington State Department of Transportation (WSDOT)
Contractor: Guy F. Atkinson
Engineer: WSDOT; Jacobs
About an hour east of Seattle, the recently completed Snoqualmie Pass East Project in Washington is now open. It allows travelers a more efficient route from Hyak to the Easton area, and wildlife can now pass much more safely across the highway.
Phase 1 of the project, Hyak to Keechelus Dam, is a 15-mile long corridor along Keechelus Lake. Construction began in 2009, with over thirty Reinforced Earth MSE walls built between 2014 and 2019.
Two of the MSE wall structures stand out from the others. Most of the 30-plus MSE walls total about 20,000 square feet of surface area. However, one wall by itself is around 200,000 square feet. At nearly 6,000 feet long (1.1 miles) and reaching a height of 60 feet, the wall supports the eastbound side of I-90 following the curvature of the mountain around along the lake. Among the many design considerations, some of the tallest portions of the walls use a trapezoidal MSE wall design, in which the lower soil reinforcements are shorter than at the top, in a stepping fashion, in order to account for the rock cut.
The south end of the project features a wildlife crossing over I-90. A double arch bridge over the highway includes Reinforced Earth spandrel walls to support the overburden and slope the crossing on either end. This is one of several wildlife crossings along the corridor, some of which cross under the highway.
The project was a major undertaking for WSDOT, and as their website states, “Travelers will experience a safer, more efficient six-lane freeway, minimized closures as a result of avalanches and rock slides, and a smoother ride due to new pavement designed to last 50 years when all improvements are completed. Wildlife habitat on either side of I-90 will be reconnected with the installation of new bridges and culverts, protecting both wildlife and the traveling public.”