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January 22, 2019
Project: U.S. 12 Wildcat Creek Bridge replacement
Client: Graham Contracting/Washington State Department of Transportation
After more than 80 years of service, the 150-foot long Wildcat Creek Bridge on U.S. Highway 12 in Yakima County was showing its age.
The Washington State Department of Transportation’s preliminary design called for construction of a temporary bridge and a construction schedule of four to five months. The Graham/Stantec design-build team instead used an innovative design approach that centered around a 54-foot precast arch culvert structure rather than WSDOT’s standard girder bridge. This allowed the team to replace the span in just 17 days and shave one-third off the cost.
Constructed offsite and trucked in, this pre-built solution eliminated the need for custom forms and additional cast-in-place elements including foundations, retaining walls and traffic barriers all of which require weeks for concrete to cure on site.
With the precast culvert, the curing time occurred at the fabricator’s plant before construction began. This allowed demolition of the bridge and installation of the arch structure in a fraction of the time originally assumed. Additionally, the buried culvert maintains passage for fish and wildlife in this remote location.
The Graham/Stantec solution saved WSDOT $4 million.
While the immediate economic benefits of eliminating the detour bridge and shortening construction time are obvious, the decision to embrace the precast culvert design offers long-term economic advantages as well.
Arch structures are far more stable than traditional girder bridges, providing longevity with low life-cycle costs. The structure eliminates the need for expansion joints and costly associated maintenance.
It also eliminates the maintenance of exposed bridge decks and bridge deck de-icing due to the continuity of the pavement-over-arch structure. In addition, off-site fabrication allows for better quality control and tighter adherence to specifications.
Although the design required complete closure of U.S. 12, WSDOT and stakeholders gladly traded months of construction impacts for this brief closure. To determine just how long the road would need to be closed, the team built a highly detailed, hour-by-hour schedule that penciled out to 17 days of round-the-clock construction.
This 17-day window cut inconvenience to the traveling public and residents by 80 percent and eliminated the safety concerns and expense associated with managing live traffic adjacent to the project. To further minimize disruption, Stantec worked with Yakima County officials and other stakeholders to develop a detour based on a route that was successfully used on a WSDOT project during the summer of 2017 and familiar to the public.
The new arch structure adds stability, maintains natural hydrology and fish habitat, and complements local and regional aesthetics. Wildcat Creek Bridge opened to traffic four hours ahead of schedule and well before the first snowfall, restoring a reliable winter route across the Cascades.