Bridge closed for long-term repairs
On Nov. 18, 2008, WSDOT crews closed the State Route 169 Green River Bridge after determining it was vulnerable to landslides.
Emergency repairs December 2008 - July 2009
An ancient landslide from the southeast is exerting pressure on the road just south of the bridge and the south bridge pier. That pressure is causing the bridge to move.
We cleared the dirt from the south end of the bridge in December. Crews finished building a 160-foot long retaining wall to prevent further movement.
The wall is made up of 57 shafts filled alternately with concrete and lean concrete. These shafts will provide the right counter-pressure to the ancient landslide and prevent the earth from moving.
Crews are also drilling drainage systems on the south side of the road. Once shaft work and drainage work is complete, they will begin building up the road bed then pave and restripe the roadway. Drivers probably won't notice much of a change.
Previous work:
Our engineers began emergency, low-cost, low-impact work in this area in June 2008 after they noticed significant movement.
We felt we could stop the slide by draining the excess water from the hillside, installing 90 specialized soil nails and spraying concrete over the entire area. (See project photos).
However, significant rainfall in early November overwhelmed our repair work. As a precaution, we installed tiltmeters and inclinometers to measure even the smallest movements in the bridge. Our first priority is safety and the smallest movement will tell us something more significant could be right around the corner.
Why is WSDOT
repairing the slope under the Green River Bridge?
WSDOT geotechnical experts have determined an ancient landslide is applying too much pressure to the southern-most pier that supports the bridge. They are concerned that pressure leaves the bridge vulnerable to failure.
The End Result
The new barrier will further protect the bridge pier from the constant pressure of the ancient landslide.
Excessive groundwater will drain from the landslide area south of the bridge. This area is saturated every year by heavy rain which contributes to the ongoing landslide. By draining the water, we will stabilize the slope, prevent further damage to the road and protect the bridge.
Project Benefits
- Safety: Drainage pipes, soil nails and reinforced walls will stabilize the land at the south end of the bridge, protecting the road from erosion. Drainage pipes will remove excess water from the land south of the bridge and reduce slide activity.
- Long-term safety: The 160-foot long wall will prevent the soil and southern bridge pier from moving.
What is the project timeline?
- June 29, 2008: Interim repair work began
- July 3, 2008: Interim repair work completed
- Aug. 25, 2008: First phase of long-term repair began. Contractors installed additional soil nails and spray-on concrete
- Sept. 4, 2008: First phase of long-term repair complete
- Oct. 13, 2008: Construction began on the second and final phase of the repair
- Nov. 18, 2008: Bridge closed for unforseen long-term emergency repairs
- Dec. 8, 2008: Excavation work began on the south end of the bridge.
- March 2009: Work began to reinforce the south pier.
- April 29, 2009: The installation of 57 shafts is complete. Attention turns to building the roadbed.
- Early summer 2009: Bridge will re-open by the July Fourth holiday.
Financial Information
The cost of this project is $15 million. Federal funds are allocated to repair the road. The federal funds must be spent on the road repair work and cannot be used for any other reason.
How can I get more information?
Contact:
Jamie Holter
WSDOT Communications
15700 Dayton Avenue North
Seattle, WA 98133
206-440-4698
holterj@wsdot.wa.gov
or
Aleta Borschowa
WSDOT Project Engineer
6431 Corson Avenue South
Seattle, WA 98108
206-768-5862
BorschA@wsdot.wa.gov
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