Date:  Thursday, August 21, 2008

Contact: Kris Olsen, WSDOT Communications, (206) 440-4475
Mike Askarian, WSDOT Project Engineer, (206) 768-5861

BLACK DIAMOND – Work on a long-term repair of an unstable slope under the south end of the SR 169 bridge over the Green River near Black Diamond will begin Monday, Aug. 25. Without the repair, more landslides could severely damage the roadway and the bridge. At least one lane of the Kummer bridge will remain open to traffic throughout the work. At this time, the contractor does not anticipate any need for a full bridge closure.

Lane closures

The planned lane closures are:

Monday, Aug. 25 – Thursday, Aug. 28: North and southbound traffic will alternate using one lane of the bridge during daylight hours. Flaggers will direct traffic. Both lanes of traffic will be open overnight.
Friday, Aug. 29 – Monday, Sept. 1: All lanes will be open for Labor Day travel.
Tuesday, Sept. 2 – Sunday, Sept. 14: North and southbound traffic will alternate using one lane of the bridge during daylight hours. Flaggers will direct traffic. Both lanes of traffic will be open overnight.

If contractors must close the entire bridge, one detour will be provided for passenger vehicles. A second detour will be provided for large trucks.

Two stages of repair work

The repair work is scheduled for completion by November and will be done in two phases.

In the first phase, crews will drive 90 specialized, slope-stabilizing nails into the soil around and under the southeast end of the bridge. When that is complete, crews will cover the area with a special spray-on concrete. This work will take approximately two to three weeks and should be done by Sept. 14.

In July, crews used this same method for an emergency repair. These additional nails will expand and strengthen that work.

In late September, crews will begin the second phase, which involves installing a series of drainage pipes into the hillside to drain water from the landslide area. Crews will drill horizontal holes up to 300 feet into the hillside approximately 30 feet below the surface of the land surrounding the bridge. This work will be completed in November.

“This hillside is saturated every year by heavy rain. The drainage pipes will remove some of this excess water,” said WSDOT Project Engineer Mike Askarian. “It reduces the risk of more slide activity, which threatens the roadway, and ultimately, the bridge itself.”

Retaining wall proposal ruled out

Originally, WSDOT engineers considered building a retaining wall to stabilize the slope and protect the bridge.

“We analyzed that option very carefully,” said Project Engineer Mike Askarian. “In the end, however, it was clear that a retaining wall wasn’t feasible and didn’t address the root of the problem which is too much water.”

To build a retaining wall, WSDOT crews would need to clear cut large amounts of the land to create room for large pieces of equipment. A retaining wall would also have to stretch nearly 60 feet from bedrock to the surface in order to stabilize the soil around the bridge. Engineers determined the steep slopes at the site and the size of the wall made it nearly impossible to build. It was also estimated such a wall would cost at least $5 million.

The soil-nail and drainage pipe solution will cost approximately $2 million. WSDOT has received federal money to pay for these repairs.

Drivers can find more information and regular updates on this project at www.wsdot.wa.gov/Projects/SR169/GreenRiverRepair/

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Drivers can now get real time traffic and weather information by dialing 5-1-1 from most phones. This new traveler information system builds upon the highly successful Washington State Highway hotline that managed 4.6 million calls each year. Callers can also use 5-1-1 to get statewide construction, mountain pass condition, and state ferry system information, as well as toll free numbers for passenger rail and airlines. TTY users can call 1-800-833-6388.

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