Work begins Aug. 16 to stabilize 101 at Cosi Hill slide area

By Dan Hammock • August 4, 2021 1:30 am
DAN HAMMOCK | THE DAILY WORLD Construction will begin Aug. 16 on this section of Highway 101 south of Cosmopolis on Cosi Hill. The roadway has been alternating one-way traffic since heavy rains caused it to collapse in January 2020, shortly before this picture was taken.
DAN HAMMOCK | THE DAILY WORLD Construction will begin Aug. 16 on this section of Highway 101 south of Cosmopolis on Cosi Hill. The roadway has been alternating one-way traffic since heavy rains caused it to collapse in January 2020, shortly before this picture was taken.

Relief is coming for traffic on Highway 101 at Cosi Hill.

The Washington State Department of Transportation said repairs will begin Aug. 16 to stabilize the hillside and reopen two-way traffic near milepost 78 south of Cosmopolis where the roadway has been restricted to one-way alternating traffic after a major January 2020 slide.

Heavy rains caused the roadway to sink more than 5 feet in the northbound lane, and damaged the road surface in both directions. Delays have been frequent since with traffic around the slide limited to one lane, alternating at first with stop signs, then the traffic signals currently in place.

The route is a popular freight corridor — which sits atop what the Department of Transportation describes as “prehistoric landslide” prone to washouts — between Raymond and Cosmopolis and points north.

The state “conducted a thorough investigation of the site” and decided, “Because of the frequency and severity of slide activity, a careful approach was required. (Agency) hydraulic, geotechnical and transportation experts collaborated to produce a solution that would withstand significant movement after heavy rains.”

“Our crews will place 45 steel beams up to 43 feet into the ground to form what engineers call a ‘soldier pile wall,’” said project engineer Karen Boone. “This is when the steel beams are lined up one-by one to imitate a line of soldiers.”

The same solution was implemented in a previous slope stabilization project in 2015 along Highway 101 at Rock Crusher Hill south of the current slide, near Artic.

A larger-scale bank stabilization project less than 1,000 feet north of the current work area was completed in June of 2020. There, the $10 million project included 576 shafts that were drilled 20-50 feet deep and filled with close to 29,000 tons of rock to stabilize the bank on the southbound side of the hill. All told, 3.7 miles of shaft were drilled.

The current $5.8 million slope stabilization contract was awarded to Quigg Bros, Inc. earlier this summer. The funding comes from preexisting state transportation funds.

Travelers can expect to see weekday, daytime construction. The temporary signal will remain in place to alternate traffic through the spring of 2022, when most of the work is expected to be complete. Any highway closures will be announced in advance. No work is currently scheduled for weekends or holidays.

Travelers planning to use the route during the construction period should follow the agency’s regional Twitter page at twitter.com/wsdsot_tacoma, and sign up for email or text alerts specific to Grays Harbor County at https://public.govdelivery.com/accounts/WADOT/subscriber/new?topic_id=WADOT_333.