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WSDOT addressing SR 401 slide

 

March 11, 2021

WSDOT photo

A slow moving slide started moving after February storms and led to the closure of SR 401. Washington State Department of Transportation (WSDOT) geotechs are studying the dynamics of the slide to prepare a plan to stabilize it.

SR 401 between Naselle and Megler was closed in late February after a particular section around milepost 4.5 become too unstable to safely support the vehicles passing that way each day, frustrating travelers in the region.

The Washington State Department of Transportation has been tracking the slope at that location for about 20 years, WSDOT Project EngineerJoanna Lowrey said on Monday, along with about 3,400 other sites around the state.

"It is considered a slow moving landslide, so typically our maintenance takes care of what little displacement we see over the years," Lowrey said. "This one was actually scheduled to start design work next year. We were going to build it in 2024, but nature had a different plan for us. We do have a budget, we have it programmed, we are just going to have to advance the funds a little bit and get it moving right now instead of two years from now."

Survey crews have already started mapping the entire slope to see what is going on and geotechnical drillers are out this week doing bore holes so they can physically see where the failure planes are. It's not simple, Lowrey pointed out, because they can't just drill on the roadway. They have to get onto the hillside as well, and do it safely, which takes time.

"All that feeds into the design that we do to figure out what the shape of this landslide is, so that we can design the best solution for that location," Lowrey said.

The survey and drilling work will take several weeks, and the modeling and design work can take several months.

"Right now [the road] is closed," Lowrey said. "We are looking at the possibility of doing a one lane opening. We'd have to fill in that uphill ditch, if possible, to get enough room to get folks through. We are looking at that to see if that can be safely done."

"I'm keeping my fingers crossed," she continued. "There is absolutely no guarantee that we will be able to do it, but that is part of what we are hoping the drilling will tell us. In the next few weeks we will model it and see if adding enough weight of vehicles and barrier and things on top, if it can be safely done."

"We've got a lot of procedures in place to make sure we are making safe decisions for the traveling public," Lowrey said. "We don't want to ever open a roadway that we are not confident can be safely maintained and even if we opened a bypass, if we see movement again in that slope we may have to close it again. We are doing our best to keep people moving but we also want to keep people safe."

Lowrey responded to questions about using local logging roads as a detour.

"There are active logging roads right now, and I know that the logging companies are using them," she said. "My understanding is that right now there is not one that goes all the way through. The other consideration with logging roads is that they are not designed for the typical vehicle. They are not designed to the kind of standards we put on the state highway. We would not be willing to take the liability of telling people that that is a safe way to go. And we have no ability to tell the logging companies that they have to let us use their roadway, even if we wanted to do such a thing."

For now, travelers are advised to use the ferry or take US 101, but to be aware that a contractor for WSDOT is currently working on a culvert that failed on US 101, about a mile north of the Astoria-Megler Bridge, and that is slowing traffic.

For more information and to sign up for updates on the 401 stabilization project, go to https://wsdot.wa.gov/projects/sr401/bean-creek-bridge/home

 

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