A guardrail on Highway 20 hangs suspended in air after a May 1 mudslide swept away soil below the road about seven miles east of Loup Loup summit.
WSDOT says not to expect ‘quick fix’
A road construction company began bringing in equipment last weekend to repair a washout on Highway 20 that has reduced the roadway to one lane east of Loup Loup Summit.
A mudslide on May 1 eroded earth below the highway about 7 miles east of the summit, leaving the outer lane and guardrail suspended in air. Traffic through the damaged section is controlled by temporary stop lights and is expected to remain limited to one lane of alternating traffic while repairs are underway.
The Washington State Department of Transportation (WSDOT) has hired Hurst Construction of East Wenatchee under a $1.3 million, 30-day emergency contract.
“This is not going to be a quick fix,” said Jeff Adamson, a WSDOT spokesman. “We’re looking at 20,000 cubic yards of materials that will need to be brought in and placed — that’s about 2,000 dump truck loads.”
If the repairs are not completed within a month, WSDOT will seek bids to continue the work, Adamson said.
The washout occurred at milepost 222.4, about a mile east of a stretch of road that was damaged by mudslides two years ago and required about four months to repair. Those slides were triggered by rainstorms, but WSDOT geotechnical engineers determined that this month’s slide was a result of ground water that saturated soil below the road and caused the washout.
“Water always finds its easiest path. In this case there’s water about 40 feet deep from the road level that used to come down somewhere into a culvert. This water has found itself a new route down to Loup Loup Creek,” Adamson said. The water carried about 15,000-20,000 cubic yards of mud and rocks hundreds of feet toward the creek that runs below the highway.
Geotechnical crews with WSDOT have installed sensors under the remaining lane. “It has remained stable since the event happened,” Adamson said. He estimated that the damaged stretch of road is less than one-quarter of a mile long.
Hurst Construction began mobilizing equipment for the repair job last weekend. The first step will be constructing a temporary road down the slope near the damaged section of Highway 20 to rebuild the eroded hillside from the bottom up. The road needs to accommodate large dump trucks carrying loads of rock and dirt.
Fill material needed
The time required for the repairs will depend in part on where and how quickly the fill material — including large “rip rap” boulders, smaller rocks and gravel — can be found and transported. “Hurst and our people are doing what they can to locate the best place,” Adamson said.
The repair work is not expected to require installation of new culverts, because porous rock that will be placed under the restored roadway is expected to allow for future runoff, Adamson said.
Construction crews are working Monday through Saturday. “Some full closures and detours are likely to be necessary at stages of the project,” including during repaving, Adamson said.
Following rainstorms in April of 2017, a 16-mile stretch of Highway 20 was damaged between milepost 207 west of the summit to milepost 222 east of the summit. The debris flows triggered by rain were exacerbated by impacts of wildfires, particularly the Carlton Complex Fire of 2014, that burned away vegetation, and in some areas damaged soil so badly that it was unable to absorb moisture. A total of nine slides required almost four months of repair work and the highway remained closed for three months.
