In our last post, I told you about using a large drill to create deep shafts for the foundation of the bridge. Here’s what happens next.
Engineers determine how deep to drill each hole based on the strength of the rock required to support the column. The average depth of the shafts for the northbound Willamette River Bridge is 35 feet, but two are as deep as 70 feet
Once the drill reaches the required depth of the shaft, a steel rebar-reinforcing cage is lowered into the hole. These cages weigh between 13,000 and 28,000 pounds.
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| Crews lower one of the steel rebar-reinforcing cages into the drilled shaft before filling it with concrete. |
With the steel cage installed, concrete is poured into the hole and allowed to cure.
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| Workers pump concrete into the drilled shaft to form the shaft for the columns that will soon follow. |
The process of drilling and pouring the bridge shafts take a little over three months from the time the drill is moved onto the site until all 22 shafts are drilled and poured.
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