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 travel much more safely across the highway. Snoqualmie Pass Opens Improvements for Drivers and Wildlife
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 trap- ezoidal 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 MSE walls 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 undertak- ing for Washington DOT, and as their website states, “Travelers will experience a safer, more efficient six-lane freeway, minimized clo- sures as a result of avalanches and rock slides, and a smoother ride due to new pavement designed to last 50 years when all improve- ments are completed. Wildlife habitat on either side of I-90 will be reconnected with the installa- tion of new bridges and culverts, protecting both wildlife and the traveling public.”
The 1.1-mile long MSE wall supporting I-90 East
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csengineermag.com
november 2020
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