Yakima’s Railroad Grade Separations Project was recently named a 2016 Public Works Project of the Year by the American Public Works Association (APWA). The project is being honored with APWA’s Project of the Year award in the Transportation category at a cost between $25 - $75 million. This award honors agencies that include roads, bridges, transit, and traffic calming projects.
For 2016, the team of winners includes the City of Yakima, WA as the managing agency; Apollo, lnc., Mowat Construction, as the primary contractor; and BergerABAM as the primary consultant, who will be presented with the award during APWA’s 2016 PWX Conference Awards Ceremony in Minneapolis, MN during August 28-31, 2016.
The APWA Public Works Projects of the Year awards are presented annually to promote excellence in the management and administration of public works projects, recognizing the alliance between the managing agency, contractor, consultant and their cooperative achievements. This year, APWA selected projects in five categories in the Small Cities/Rural Communities area: Disaster/Emergency, Environment, Historical Restoration, Structures, and Transportation.
The Yakima Railroad Grade Separations was a public works project that entailed the construction of two underpasses of the BNSF railway, one for eastbound traffic on Lincoln Avenue and one for westbound traffic on Martin Luther King (MLK) Avenue. The underpasses provided unobstructed traffic flow under the BNSF railway, which is anticipated to see an increase in rail traffic in the coming years.
Each grade separation spans roughly three city blocks and is constructed using a series of drilled secant pile retaining walls and concrete pile caps used to retain the existing ground elevations on either side of the project. A tremie-poured concrete bottom seal was also incorporated into the design to prevent water infiltration into the newly constructed underpass. Due to the high water table within the project limits a lift station was constructed to remove stormwater from the underpass to a series of retention and infiltration ponds.
The primary project challenge involved the use of ground improvement methods s to construct the Lincoln bottom seal. The team initially allowed the contractors to select one of two possible methods that were considered suitable for the soil conditions at the project site. Permeation grouting was initially selected but did not provide the desired results. Working together, the project team developed a third approach that involved the use of an existing technology in an innovative way. The discovery of this design solution revolutionized the construction of bottom seals. The new methodology would come to be known by the project team as “drill and fill.”
The existing technology constructs augercast piles with a continuous flight auger (CFA). A CFA is a large-diameter (four-foot diameter for this project) drill bit with continuous drill spirals around a hollow central pipe. An augercast pile is constructed by drilling the auger into the ground without bringing any of the soils to the surface (like a corkscrew into a cork). When the auger reaches the desired depth, concrete is poured down the central pipe and fills the void created as the auger is lifted with all the soil held on top of the auger’s spirals. This results in a concrete column—an augercast pile—in the ground.
The primary issues were that the power of the drill equipment only allowed for limited cutting (secanting) into adjacent columns, and all secanting had to be balanced on the opposite sides of any pile being drilled to keep the drill bit from deflecting out of vertical alignment. This method was much less risky than ground improvement methods because it almost totally replaced the existing soils with concrete (96 percent of the seal volume).
For more information on the APWA 2016 Projects of the Year, please contact APWA Media Relations and Communications Manager, Laura Bynum, email@example.com, or call 202.218.6736.
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