WSDOT goes with unique retaining wall design on S.R. 14

Bridges Case Studies
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Camus and Washougal, Wash., are suburbs of Portland, located on the banks of the Columbia River, near the foot of the Cascade Mountains. State Route 14, also named the Lewis and Clark Highway, is a main artery that runs through both towns. A well-traveled 3-mile section of highway narrowed at the West Camas Slough Bridge, causing a bottleneck that resulted in congestion and many collisions. The highway and bridge needed to be widened from two to four lanes, and new on- and off-ramps were necessary. To add to the challenge, the location is very busy and the roads needed to be kept open during construction.

 

The Camas-Washougal project was originally proposed in 2008 with precast concrete panel walls, but was not completed due to budget constraints. After regaining traction in 2009, the project was put up for a value-engineering analysis. Oregon Brick & Block proposed a segmental retaining wall (SRW) design that utilized Allan Block and Stratagrid SG200, a high-tenacity polyester (PET) geogrid made by Strata Systems. Prior to this project, WSDOT projects had only incorporated SRW systems having three- to six-degree wall batter for on- and off-ramps. However, site constraints for S.R. 14 would only accommodate a near vertical wall batter. The Allan Block system, incorporating Stratagrid, not only allowed for a one-degree wall batter to be utilized, but also resulted in a $5-sq-ft savings compared to the original precast concrete panel walls. After seeing the cost savings and engineering capability of the design presented, the project was awarded to Oregon Brick & Block.

 

Oregon Brick & Block along with project contractors, Tapani Underground, and geogrid supplier, Strata Systems, collaborated to construct the first-ever Washington State Department of Transportation approved one-degree batter SRW. The height of the ramp walls reached 20 ft and SRW units were supplied with traditional split-face aesthetic consistent with the adjacent bridge structures.

 

The 80,000-sq-ft project was completed in 2012. According to the WSDOT, “The project improved safety along S.R. 14 by adding median barriers throughout the project area, increasing capacity and reducing travel times to accommodate residential, commercial and industrial growth. State Route 14 will better serve current and future commuter traffic demands and better accommodate the movement of goods and services.”

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