10,000 dump trucks filled with rocks key to Highway 530 fix at a cost of $6 million

Published 9:00 pm Monday, March 20, 2006

OSO – Rocks, and lots of them, are key to a plan engineers have come up with to stabilize a mushy hillside on Highway 530 before it gives way.

The new plan calls for building a giant rock buttress on the downhill side of the highway, said Travis Phelps, a spokesman for the state Department of Transportation.

The design calls for enough rock to fill 10,000 dump trucks – 100,000 cubic yards of rocks, Phelps said.

Shifting, wet ground for the past six weeks at a spot known locally as Skaglunds Hill has caused engineers to worry that a landslide could cut off Darringtons main access to I-5, forcing a 110-mile round-trip detour for thousands of commuters.

A big slide could even disrupt one of Seattles main power sources if towers for high-voltage power lines nearby were to collapse.

The rock buttress is designed to prevent that, Phelps said.

This thing is going to be about 500-feet wide, he said. Its going to stretch up the hill toward the roadway about 200 feet, and itll be about 30 feet deep in a couple different spots.

Including installation of about 30 drainpipes to dry out the hill, the project is expected to cost $6 million, Phelps said.