US 101 - N of SR 107 - Stabilize Slope

Project news

  • This section of US 101 in Grays Harbor County, also known as Cosi Hill, is the site of a large, slow-moving earthwork under the highway. Despite ongoing maintenance efforts, further attention is needed to repair the slide-prone area. The goal of this project is to stabilize the slope adjacent to the road to reduce the risk of earth movement that could lead to unexpected roadway closures.
  • From 7 a.m. to 4 p.m., Thursday, Oct. 24 drivers will encounter one-way alternating traffic with flaggers for pavement repairs. In early October 2019, crews noticed movement in the ground again resulting in a slight crack of the pavement. The roadway is still safe for passage and poses no threat to travelers at this time. All shaft work is complete and drillers are demobilizing from the site for winter. More substantial paving will be  done when dry weather allows again (most likely spring 2020).
  • Crews will drill 6-foot-diameter columns nearly 50 feet deep. The columns will be filled with rock to dramatically stabilize this stretch of highway. Drivers will encounter shifted lanes and reduced speeds during this two-year construction project.
  • Travelers who wish to receive updates on this project and other state highway projects in Grays Harbor are encouraged to sign up for Grays Harbor County maintenance and construction email alerts.

Needs & benefits

Why is WSDOT stabilizing a slope on US 101 north of the SR 107 interchange in Cosmopolis?
A stretch of US 101 near milepost 79 sits on a pre-historic landslide and has experienced chronic roadway settlement, leading to repeated lane closures. As a result, maintenance crews have repeatedly patched the roadway through the area, but additional geotechnical earthwork is required for more permanent repairs. Those temporary fixes have proven to only last until the next heavy rainstorm hits.

The End Result
To stabilize the hillside under the highway, contractor crews for WSDOT will drill shaft columns up to 50 feet into the earth. About 600 shafts will form a buttress to support the roadway. Crews will also address ongoing drainage concerns and reconstruct the embankment slope beyond the south edge of the roadway. The rock-filled shafts will help securely hold the hillside in place, reducing the potential for the roadway pavement to move. Finally, crews will reconstruct and repave the roadway.

Project Benefits
Slope stabilization of “Cosi Hill” is intended to reduce the potential for slide-related closures at this location. This work also is expected to reduce maintenance costs associated with regular leveling, patching and repaving the road.


  • Spring 2019: Project advertised for competitive bids.
  • May 10, 2019: Contract awarded to Rognlin's Inc. 
  • Summer 2019-Fall 2020: Construction
  • Late fall 2020: Most work complete.


Financial Data for PIN 310121G
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $8,880
CWA $0
Total $8,880


Karen Boone
WSDOT Project Engineer 

Tina Werner
WSDOT Olympic Region Communications

US 101 Cosi Hill Thumbnail

US 101 Cosi Hill current condition
Current condition