Project Facts
- 9,000 cars use the bridge every day.
- Phase one: a short retaining wall built during emergency repairs in July is expanded
- Phase two: Long drainage pipes will be drilled into the slope to remove excess water from the landslide area.
November 2008
- SR 169 is closed at the Kummer Bridge over the Green River as of 7 p.m. Tuesday, Nov. 18. It will remain closed for up to six months for extensive repairs.
- WSDOT geotechnical experts have determined that the structure is vulnerable to significant land movement. The bridge is too unstable to allow traffic to safely use the bridge.
- Emergency closure detour
Bridge closed for long-term repairs
The State Route 169 Green River Bridge will close for six months starting Nov. 18 to repair and strengthen its supports in unstable soils.
We sprayed concrete over soil nails this summer to try to control the unstable soils beneath the Green River Bridge piers. WSDOT geotechnical engineers believe heavy rains may have caused the soil to move more than expected. The force of the moving soils proved greater than the repair work and is pushing on the bridge pier.
WSDOT engineers are concerned that the soil may not be able to support the bridge pier. If the soil slides, the pier could move with it. Significant emergency repairs are needed to keep the bridge safe.
The long-term repairs will take place in two stages.
Stage 1 repairs
Crews will remove excess water by clearing trenches, unplugging manholes and installing pumps to help drain water from the unstable hillside.
Stage 2 repairs
Crews will excavate the soil that is putting pressure on the bridge pier. They will dig out a section of roadbed 30 feet deep and 300 feet long just south of the bridge and replace it with lighter weight material.
Cost: All the emergency repair work will be done as an emergency contract, estimated at approximately $10 million.
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A slope underneath the south approach to the Green River Bridge (Kummer Bridge) on SR 169 between Enumclaw and Black Diamond is slowly eroding away. We've been monitoring the slide for several months, but the damage accelerated in summer 2008.
Stabilizing the slope to protect the road and bridge will require multiple phases of work.
Phase one: We installed approximately 63 specialized soil nails below the bridge and covered it with shotcrete, a spray-on concrete. There are now more than 90 soil nails in place around the southeast end of the bridge. Crews completed phase one in early Sept. 2008.
Phase two: to build drill drainage pipes into the slope under the bridge to remove the excess groundwater that is causing the land to slide around the bridge. Work began on Oct. 13.
Why is WSDOT
repairing the slope under the Green River Bridge?
WSDOT geotechnical experts have determined the slope needs to be repaired to prevent further erosion and improve stability of the roadway.
In July, crews built a short retaining wall in the most vulnerable area using "soil nails" and shotcrete, a spray-on concrete designed to help shore up unstable slopes.
The long-repair involves installing more soil nails and shotcrete to expand this area. Contractors will then install a series of drainage pipes into the hillside to drain water from the landslide area.
These horizontal drainage pipes will extend up to 300 feet into the hillside and up to 30 feet below the surface of the land surrounding the bridge. The pipes will be installed in 3 areas at the southern end of the bridge.
Each area will have six to ten pipes. The water will be carefully drained into the Green River. Because it is groundwater, it is clean and there is no environmental impact to the river. This work will be completed by November.
WSDOT design engineers originally examined building a large retaining wall. However, they determined it would have to stretch nearly 60 feet from bedrock to the surface in order to stabilize the soil around the bridge. Engineers also determined the steep slope and heavily wooded area made it nearly impossible to build and would cost at least $5 million.
The End Result
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 and soil nails 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.
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: Construction begins on the second and final phase of the repair
- Nov. 18: Bridge closed for unforseen long-term emergency repairs
- Spring, 2009: Bridge will re-open, emergency repairs complete.
- Summer, 2009: Stage two of project complete.
Public Involvement
Your thoughts and opinions are important to us. If you have questions or comments, please contact the project office.
Environmental Protection
During design and construction we will make every effort to assess and minimize negative environmental effects of this project.
Please visit the WSDOT Environmental
Services Web site for more information.
Increasing safety is one of our priorities
The stabilized slope will reduce the risk of road erosion and bridge damage.
Will this project impact tribal resources?
At WSDOT we seek to address the concerns of the tribal nations using the process outlined in Section 106 of The National Historic Preservation Act and the WSDOT Tribal Consultation Policy adopted in 2003 by the Transportation Commission as part of the WSDOT Centennial Accord Plan.
Financial Information
The cost of this project is $2 million. WSDOT has received federal highway funding to pay for these repairs.
How can I get more information?
Contact:
Broch Bender
WSDOT Communications
15700 Dayton Avenue North
Seattle, WA 98133
206-440-4702
Benderb@wsdot.wa.gov
or
Mike Askarian
WSDOT Project Engineer
6431 Corson Avenue South
Seattle, WA 98108
206-768-5861
AskariM@wsdot.wa.gov
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