NEAR LAKE STEVENS, Wash. - In early November a sinkhole opened up along the shoulder of the westbound lanes of U.S. Highway 2 just east of the Lake Stevens exit onto State Route 204.
The reason for the sinkhole is that a culvert pipe diverting runoff from the hills above Highway 2 had rusted through. This let dirt and rock flow in, creating a void above the pipe and resulting in a small collapse of the land.
This sinkhole was off the side of the road, but a sinkhole opening up under the highway itself could be a bad thing causing dips and sags - dangerous to drivers.
Road maintenance crews quickly filled in the hole, and then called out the camera.
I could watch all that mud and rock in the pipe on a TV monitor, as a special crew from the Washington State Department of Transportation out of Olympia put a remote camera down inside.
The $75,000 camera is about the size of a medium-size dog, weighing 60 pounds. It rides on a four-wheel-drive chassis that can drive through trouble. The camera itself is mounted inside a metal housing and can turn at every angle, and surrounding it are banks of small, very bright lights.
WSDOT has owned the camera for a few years, but there's a new emphasis on using it because a lot of culverts installed during the great highway expansions of the 1950s and '60s are all coming to the end of their lives at roughly the same time.
In WSDOT's Northwest Region, which includes King, Snohomish, Skagit and Whatcom counties, there's about one sinkhole per year, says Dave McCormick, an assistant administrator.
Today, the crew not only inspected the suspect pipe, but inspected five other culverts in the area.
"If one fails, we typically used the same material on others," says McCormick.
He says pipes that are built in soil of similar chemistry, or have solder on in similar conditions with high water flow or other common characteristics, can often be in similar condition.
It happens that this cluster of culverts under this section of Highway 2 runs at a steep angle.>/p>
Steve Russell is a Maintenance & Operations Assistant Superintendent and says it's the upper 10 feet of pipe that seem to be rusting out the fastest, and he says the steep angle appears to have something to do with it. He says the angle appears to allow more soil surrounding the pipe to be flushed away faster than where the pipes run horizontally. In this case the portion of pipe under the road appeared to be in relatively good shape. Some of these culverts are running for more than 125 feet under the heavily used east-west highway.
Repairs can vary. If the damaged pipe is still round, it can be sleeved, meaning a rust proof plastic pipe can usually be slid inside the rusting steel culvert at a relatively low cost. But if the pipe has collapsed inside, contractors may have to dig up the road to get at and replace the pipe, and the price tag for that is usually a lot higher.