A five-mile stretch of state Route 7 that was closed by a slide on June 7 will remain closed through the summer, the state Department of Transportation reported Tuesday. The Eatonville-area closure extends from state Route 161 to Alder Lake.
Steep terrain and a still-unstable hillside are challenging geotechnical experts as they continue to assess how expansive the slide was and why it occurred.
Kevin Dayton, the transportation department’s regional administrator, said it’s likely a soil nail wall will have to be installed. Soil nail walls reinforce existing soil by installing threaded steel bars into slopes or cuts as wall construction proceeds from top down.
“It could be August before it is designed and ready to be constructed and October until it is completed,” Dayton said. “Until we know the hillside is stable, we won’t open the roadway.”
Unlike typical highway work, this project is more than 100 feet up from the roadway at an approximate 45 degree angle, noted transportation department spokeswoman Claudia Bingham Baker.
To assess the condition of the slide, Bingham Baker said, a geotechnical team drilled three holes up to 200 feet deep above the slide site to determine subsurface soil and bedrock conditions. They also installed instruments to measure any movement and groundwater conditions above the slide to help formulate a plan on how to stabilize it in the long term.
Next week more drilling will occur within the slide mass itself to gather more data about the slide, Bingham Baker said.
In the meantime, a signed detour around the closure adds about 10 to 15 minutes to trips for approximately 1,600 drivers a day.