Work to repair the 80-year-old State Route 169 Green River bridge is proceeding ahead of schedule.

Tri-State construction crews finished excavating 20,000 truck loads of material from an area just south of the bridge six days early. Workers are now planning for phase two.

The Green River bridge, also knows as the Kummer Bridge, which connects Black Diamond and Enumclaw, has been closed since Nov. 18 when engineers noticed small but significant movement in the south pier and in the soil which support the bridge. Engineers determined the bridge was too dangerous to allow traffic to cross.

The Washington State Department of Transportation tried low-cost, low-impact work to improve bridge safety. Only recently, with the onslaught on heavy rain in early November, did the landslide cross the tipping point and force extraordinarily dangerous movement in the soil.

Geotechnical engineers are working to stabilize a large ancient landslide that has been pushing the bridge slowly to the southwest for years.

The first goal was to alleviate the pressure this landslide exerted on the bridge pier. To do that, crews excavated a large piece of land 20-feet deep by 80-feet wide by 200 feet long. Removing the wet soil solved the first part of the problem. At a later date we will return and fill the area with lightweight material to relieve pressure on the bridge.

The next phase is significantly more complicated. Crews will drill more a series of 55 shafts deep into the bedrock. Some shafts will extend 90 feet, others will extend 45 feet. They will fill these shafts with varying strengths of concrete. These shafts will then tie together to create a retaining wall measuring 160 feet long. It is this wall that will protect the pier.

The repair work has received emergency federal funding. This project will cost $15 million.

Next steps

A wall of this size in an area with wet, shifting soil requires detailed, highly accurate design plans. While bridge engineers have a plan, it will take another few weeks to finalize the details of the work. During this time, local residents will not see any workers on site. The work continues, but not in the field. Crews will be on site in February and will work around the clock to build this retaining wall.

Local drivers, emergency services and freight

The Kummer Bridge is vital to the communities of Black Diamond and Enumclaw. It carries an estimated 9000 trips each day including emergency services and law enforcement.

Detours

There are two detour routes: one for passenger vehicles and one for commercial trucks. Drivers can download the maps at: www.wsdot.wa.gov/Projects/SR169/GreenRiverRepair/Detour.htm

Drivers can follow project progress at: www.wsdot.wa.gov/projects/sr169/greenriverrepair/ and see pictures at: www.flickr.com/photos/wsdot/sets/72157610963340028/