When a landslide ripped away part of the foundation below a section of state Highway 501 outside Ridgefield late last month, repair crews went to a familiar game plan.
They’d been here before. And they knew it wasn’t going to be a quick fix.
“You can’t just do a little patch on the top, or it’s going to fail you again,” said Lori Figone, a project manager with the Washington State Department of Transportation. “You can’t do it partial.”
Last week, construction crews began the process of completely rebuilding the slope to the south of the highway. They’ll first remove about 3,500 cubic yards of soft, unstable material, excavating down to more solid ground. Then workers plan to brace and build the foundation back up with rock, eventually repairing part of the roadway itself.
Crews used a similar approach on the same highway, just a few hundred yards away, following another slide in 2006, Figone said.
The two incidents didn’t send debris onto the roadway from above. Rather, in both cases, material slid out from under it, moving down the bank below.
“It’s just an active slide area,” Figone said.
Last month’s slide followed a wetter-than-normal December, which left the ground more unstable than usual. The resulting shift carved the slope right up to the road, leaving some pavement hanging over a precarious edge. Underground cables were exposed. At one point, Figone said, “all the guardrail posts were just hanging in the air.”
WSDOT initially reduced the speed limit, then closed the eastbound lane between
Smythe Road and North Reiman Road. A temporary traffic signal now directs drivers on the one-lane highway.
Crews with contractor Tapani Underground will work seven days per week until the job is done, likely in February, Figone said. In the meantime, drivers can expect slow going at times, and a parade of dump trucks taking excavated material to a disposal site elsewhere in the county. That stretch of highway typically sees about 4,900 vehicles per day, according to WSDOT.
Despite the wet conditions that contributed to the slide, a mostly dry, cold January has so far helped make conditions less sloppy for workers. WSDOT is also temporarily diverting an unnamed stream around the work site.
Such emergency jobs always carry some degree of uncertainty, said WSDOT spokeswoman Heidi Sause. They also can deliver a blow to the agency’s budget. The latest slide repair is expected to cost about $500,000, paid through state highway maintenance and preservation funds, according to WSDOT.
“They’re unplanned, and they’re not cheap fixes,” Sause said.
Crews expect to have the work wrapped up in the next two to three weeks.