Final Drilled Shaft Completed on Lynnwood Link Extension

On December 11, Sound Transit’s $800 million Lynnwood Link Extension (L300) project reached an important milestone as contractors completed the last of the 110 drilled shafts required for the northern segment of this light rail expansion.

Sound Transit, the public transit authority for the greater Seattle, Washington region, is expanding its network with 8.5 miles of light rail line between Northgate and Lynnwood, north of the city. In 2016, a new station opened at the University of Washington, and an additional section of track is pushing the line to Northgate in 2021. The Lynnwood Link Extension is the next phase of northward expansion into Snohomish County, with four new stations scheduled to open along the line in 2024.

Since 2010, GeoEngineers has been working closely with Sound Transit on the LLE through every phase of design; from alternatives evaluation to conceptual, preliminary and final engineering. The project team, led by Tim Bailey and Dan Campbell, completed an extensive geotechnical investigation along the proposed light-rail corridor and gave geotechnical recommendations for elevated guideway foundations, retaining walls, stations, parking garages, stormwater facilities and more.

“It’s been a long road,” says Tim. “We started a decade ago with just lines on a page connecting Northgate to Lynnwood—getting to the point where we have shafts and bridges out there is pretty cool.”

The project began construction about 18 months ago. During that time up to four drilling teams from Malcom Drilling worked long hours to complete the shafts, often close to active roadways and the I-5 freeway, or even drilling over water from a work trestle. Simultaneously, there have been other crews working on thousands of linear feet of retaining walls. GeoEngineers has provided full-time construction monitoring and guidance for the drilling, as well as the construction of thousands of linear feet of retaining walls along the route.

Tim expects GeoEngineers’ construction observation to last well into 2021, at least, and Sound Transit is still targeting a 2024 completion.

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