Cosi Hill slope stabilization completed; lanes fully opened

Work has been completed on slope stabilization along Cosi Hill.

Following extensive work on Highway 101 between Aberdeen and Raymond, the Washington State Department of Transportation says that crews finished paving on Friday, May 20. 

Once the smoother surface was in place, crews reopened the highway to two-way travel following intermittent lane closures from hillside damage and roadway repairs. 

Construction is now complete and no additional lane closures are scheduled for this slope stabilization project.

Cosi Hill has seen lane reductions with alternating traffic since January 2020 due to chronic roadway settlement that required two separate repair projects. 

Previous low-cost repairs had only been lasting a short time and were not addressing the 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.”

The Washington State Department of Transportation says that the highway sits on a prehistoric 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.”

Crews will install 300 feet of fencing on top of the retaining wall in June. The fence work will not affect US 101 travelers.