That’s a wrap! US 101 Cosi Hill slope stabilization work complete

COSMOPOLIS – A smoother ride has arrived for US 101 travelers between Aberdeen and Raymond. Crews finished paving at milepost 78 in Grays Harbor County on Friday, May 20. The highway reopened to two-way travel following previous intermittent lane closures from hillside damage and then roadway repairs. Construction is now complete and no additional lane closures are scheduled for this slope stabilization project.

This overall stretch of roadway, often referred to as “Cosi Hill,” had been reduced mostly to a single lane with alternating traffic since January 2020 due to chronic roadway settlement that required two separate repair projects close in proximity. The now-complete milepost 78 work is the second of those projects. The Washington State Department of Transportation highway sits on a pre-historic landslide and heavy rains triggered the roadway to drop more than five feet.

“We appreciate the public’s patience while crews worked last summer and fall to stabilize Cosi Hill,” said WSDOT Aberdeen Project Engineer Jason Mettler. “We know lengthy lane closures are challenging for travelers, but they were needed to complete this $4.3 million investment to stabilize the hillside and reduce the likelihood of further highway settlement.”

The solution

The frequency and severity of slide activity at this site required a repair project that would better withstand significant movement after heavy rains. Previous low-cost repairs proved to only last one season and did not address the historical underlying causes and road settlement.

The long-term fix to the road settlement designed by WSDOT engineers included installing “solider pile walls” to stabilize the hillside.

“Crews installed 45 steel beams roughly 43 feet into the ground, lined up one by one with wood timbers in between to imitate a line of soldiers,” said Mettler. “The beams and timbers were then covered by a wall of concrete for protection.”

Warm, dry weather conditions allowed crews to work diligently this week to complete final paving and striping activities.

WSDOT’s Aberdeen-based contractor, Quigg Bros., will wrap up the last few minor task items. Crews will install 300 feet of fencing on top of the retaining wall in June. The fence work will not affect US 101 travelers.

Grays Harbor travelers are encouraged to sign up for email updates. Real-time traffic information is available on the WSDOT app and WSDOT regional Twitter account.

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