US 101 - S of Cosmopolis - Stabilize Slope

Project news

  • Contractor crews will begin slope stabilization efforts at Cosi Hill beginning Monday, Aug. 16. Travelers will continue to encounter alternating traffic with a temporary signal through spring 2022. 
  • Loads are restricted to no wider than 14 feet to provide clearance.
  • Grays Harbor County travelers are encouraged to sign up for local email alerts to stay informed. 

Needs & benefits

Why is WSDOT stabilizing a slope on US 101 north of the SR 107 interchange in Cosmopolis?

US 101 near Cosmopolis has a history of reoccurring landslide activity beneath the roadway due to a chronic unstable slope. Over the years, WSDOT has invested millions of dollars into the hillside, but unfortunately Mother Nature had other plans. On Jan. 24, 2020, crews discovered more than 12 inches of roadway settlement and reduced the highway to a single lane for safety purposes. Since then, the roadway has dropped more than five feet. Crews recently corrected another unstable slope less than 1,000 feet away during the summer of 2020.

WSDOT conducted a thorough investigation of the site. Because of the frequency and severity of slide activity, a careful approach was required. WSDOT hydraulic, geotechnical and transportation experts collaborated to produce a solution that would withstand significant movement after heavy rains. Design engineers decided to implement a proven approach to this long-term fix by installing soldier pile walls to futher stabilize the hillside. Crews will secure 45 steel beams roughly 43 feet into the ground, lined up one-by-one to imitate a line of soldiers.

WSDOT implemented this solution in a previous slope stabilization project in 2015 along US 101 at Rock Crusher Hill.

Previous low-cost repairs have proven to only last one season and not addressed the underlying causes. This solution offers a more permanent repair to restore both lanes and fully reopen the highway in a safe manner for all travelers.

The End Result
A stabilized roadway will help secure the hillside, reducing the potential for roadway settlement and repeated lane closures.  


  • Late April 2021: Contract advertised
  • June 2021: Construction contract awarded to Quiggs Bros., Inc,
  • Aug. 16, 2021: Construction begins
  • Spring 2022: Most work complete


Financial Data for PIN 310178F
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $5,345
CWA $0
Total $5,345


Karen Boone
Aberdeen Project Engineer 

Tina Werner
Media Relations