LOUP LOUP PASS – Work to repair a large washout which collapsed a portion of State route 20 seven miles west of Okanogan near Loup Loup Pass began this week.
The damage occurred on May 1 when water seepage from an adjacent hillside disturbed the integrity of the roadway’s foundation, cracking and crumbling the asphalt and leaving a portion of the highway’s guardrail and its anchor posts suspended in mid-air over a newly-formed, 25-foot gulch.
Project engineer Bill Asmussen with the Washington State Department of Transportation (DOT) told iFIBER ONE News, “We believe that seepage from the other side of the roadway going underneath the roadway along with what we believe was an underdrain problem caused saturation of water underneath (the road) and is what caused the slide.”
When asked if the event occurred during a rain event, Asmussen replied, “No, it was a pretty normal, sunny day we believe.”
To perform the emergency restoration, the DOT has contracted with Hurst Construction LLC of Wenatchee, whose first task is to establish an approach to the damaged area.
“Currently, they’re doing an access road to get down to the bottom of the slide,” explained Asmussen. “From there, we’re going to establish a shear key plane, filling it in with rocks that are roughly two to three feet in diameter, very angular rock. From there, we’re going to build on top of that with some base cores and then some gravel borrow and build it up it steps.”
The project is expected to require approximately 2,000 loader trucks full of riprap and gravel in order to completely backfill the estimated 20,000 cubic yards of rock and earth which was displaced in the washout.
Crews won’t need to go very far for some of those materials, however, since there are already several large piles nearby which were left over from work that was done to repair a series large washouts about a mile west of the current one two years ago.
Geotechnical engineers with the DOT have determined that wastbound lanes through the damaged area are stable enough to allow for a single lane of traffic which is currently being signal-regulated around the clock but could soon be switching to some intervals of flagger control during daylight hours. There is also a 12-foot width restriction for all vehicles traversing the construction zone.
Emergency repair contracts through the DOT operate on a maximum of 30 days but can be extended if necessary, a step that officials say may be required to completely restore the missing chunk of SR-20 bewteen mileposts 222 and 223.