U.S. 2 keeps sinking.
A 30-foot-long segment of the highway just east of the turnoff to Index has sunk 7 feet since the Election Day flood, and it’s still slipping.
“It’s safe enough to drive on but something that you don’t want to leave this way for very long,” said Marlin Lenssen, project engineer for the state Department of Transportation.
It’s the eastbound lane that’s slipping down the hillside. The westbound lane hasn’t moved and appears to be stable, he said.
The site is monitored around the clock by DOT workers, and the speed limit through the area has been reduced to 35 mph.
On Sunday evening, the state plans to start working on a temporary fix that it hopes will hold the road together until something more permanent can be worked out, said Travis Phelps, a DOT spokesman.
The road will be reduced to one lane until at least mid-February, he said. Flaggers will alternate traffic. The road will be opened for the weekends so ski traffic can get through.
“It shouldn’t be too bad,” Phelps said. “We’re not expecting that many problems.”
On weekdays, about 6,500 cars per day pass through the site, he said. On weekends, that number shoots up to 17,500 per day, a number that’s probably even higher in the winter, when people are using the highway to go ski and snowboard at Stevens Pass.
The state plans to pound 66 giant soil nails into the slope to hold it together while it works on a permanent solution, Lenssen said.
The 40-foot-long nails will be hammered in at a slight angle – about 15 degrees – to keep the hillside from slipping.
“You want the far end as low as possible, but you can’t go too far, or it won’t hold,” Lenssen said. “Basically, you’re locking the material in place.”
The heads of the nails will be locked together in a grid for strength with concrete, Lenssen said.
A permanent fix has been difficult to design because the geotechnical engineers brought to the site had to dig 80 feet into the ground before they were able to find some solid stone.
The road surface needs to be tied into that stone or the slipping could start all over again, Lenssen said. He said the permanent fix would likely involve anchors that act like the soil nails but are much thicker and longer. They’re also pumped full of concrete that is designed to leak out and lock the anchors into the mountainside.
The temporary fix will cost about $1 million and a permanent solution will cost another $1 million or more, he said. The temporary repairs also are needed so the state can park the heavy equipment it needs to make permanent repairs without the road giving way.
It appears a culvert that runs under the road at the site has eroded, allowing water to work its way into the slope, Lenssen said.
“There may be some extra water flowing down through the soil that aggravated the problem,” he said.
The first thing the crew will do when construction starts on Sunday is install a new culvert, he said.
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