Mysterious patches along I-90 explained
Jul 19, 2016, 6:27 AM
KIRO Radio's Chris Sullivan explains what those mysterious patches are on I-90. (WSDOT)
(WSDOT)
If you’ve driven I-90 between I-5 and the Mount Baker Tunnel you might be wondering what all those off-color patches are.
This is a concrete strengthening project. This section of I-90 is made up of concrete panels, but they are not tied together.
Annie Johnson, spokesperson for the Washington State Department of Transportation, said those panels rock slightly as cars and trucks go over them because the ground underneath them is settling and moving.
Related: WSDOT is in a heated battle with erosion along the Pilchuck River
“Over time, especially with big, heavy trucks and other heavy vehicles, that dirt gets compacted, and the panels start rocking,” she explained. “Then they start to chip and crack.”
The panels act like seesaws. This project will add metal bars at the end of each panel to tie them together so they stop rocking.
It’s called a Dowel Bar Retrofit.
Johnson said they cut six slots in each panel using a giant cutting machine and then insert a bar in each.
“They do it on every panel joint,” she said. “They chip out those slots. They put the dowel bars in, and then they pour back a grout. Once that grout has hardened, they come back and grind it smooth.”
It leaves a quilt-looking effect on the road where those patches sit. The work is nearly complete between I-5 and the Mount Baker Tunnel. Similar work was done years ago on I-90 across Mercer Island.
Johnson said these dowel bars are placed in on the front-end during new road construction.
This work is all part of the project adding light rail across the I-90 Bridge and adding HOV lanes to the outer roadways. This dowel bar project is going to last a little longer than anticipated. The contractor ran out of contrast striping tape last week. They need it for the lane markings.
Unfortunately, the contractor can’t just run out to Home Depot to get a new roll.
