In addition to two graceful arches supporting the bridge, the new northbound Willamette River Bridge will have nine columns, supported by 22 drilled shafts filled with concrete, which create the foundation for the columns.
The team surveyed and staked column locations before clearing and constructing cofferdams at each site. Next, crews built platforms to accommodate a large drill rig near each cofferdam.
The drill rig can drill to a depth of 200 feet, though for this project, the average depth is 35 feet. The bit or auger attached to the drill rig varies in size, but is typically 8 feet in diameter and 6 feet long. Once the drill is positioned, the drilling takes one to two days per shaft.
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| The drill rig positioned beside the cofferdam is ready to drill one fo the two shafts at this site. |
Initial drilling is usually through soft material, which is removed from the hole. To prevent soil from falling back into the hole, workers insert a temporary steel casing (below) before pouring the shaft.
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