A little over a year after a landslide covered the roadway near Speelyai Bay on Lake Merwin, state Highway 503 has reopened.
The Washington State Department of Transportation initially estimated the emergency repair would cost between $1 million and $1.5 million, but the final expense was $3.85 million.
“Some of the work took longer than we initially anticipated. As the contractor removes layers of rock, you never know what layers and fracture lines are back there,” said WSDOT spokeswoman Tamara Greenwell.
On March 13, 2017, after a month of heavy rain, the steep hillside above the highway gave way, sending trees and earth down onto the roadway and leaving a 10,000-ton rock slab the size of a basketball court looming precariously above and threatening the roadway.
“Freeze/thaw cycles can cause sections of rock to break apart. That’s what we think happened in this case — and happens often — huge amount of rainfall plus freezing and thawing, happened over several seasons,” she said.
Typically, WSDOT will clean up after a landslide by scraping the roadway clean enough to reopen the road, but in this case the rock slab posed an uncertain threat. The scope of the emergency repair was larger than WSDOT expected and more rock had to be removed than initially thought.
Due to the dangers present, crews used drones and LIDAR, a surveying technique involving lasers, to assess the situation and craft a plan. In order to remove the slab, workers started at the top, rappelled down the slope and chipped away the rock slab by hand, and on a few occasions, they used small explosives to break it apart.
When that work was finished, crews set to stabilizing the slope over the long term anchoring and bolting the rock wall in place.
The stabilization work finished a few months ago. The roadway also had to be repaved and restriped, but WSDOT had to wait until late last month for decent enough weather to do so.