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The strongest oscillator in the world is digging more than 200 feet beneath the bottom of the Willamette River as part of work to seismically upgrade the Abernethy Bridge, which carries Interstate 205 between West Linn and Oregon City.

The 200,000-pound machine, affectionately named 鈥極scar the Oscillator,’ is digging to allow construction of 12-foot shafts for the bridge’s new support columns.

Abernethy Bridge, which opened in 1970, is one of nine bridges being seismically strengthened or replaced as part of Oregon Department of Transportation‘s I-205 Improvements Project.

Other work includes adding a third travel lane to seven miles of the freeway between Stafford Road and Oregon Route 213 to reduce congestion. Approximately 100,000 travelers move through this section every day, said Della Mosier, deputy director of ODOT’s Urban Mobility Office. The area suffers from traffic congestion around seven hours each day and sees about 150 crashes each year.

Kiewit Infrastructure is leading the construction, and Malcolm Drilling is contributing to the project.

Crews need about three to four weeks to create each shaft for the support columns, and so far, they have completed six of 28. The process starts with Oscar digging by oscillating back and forth. That advances a steel casing downward. The casing will protect the hole from caving in when being excavated and later become the sides of the foundation in its final configuration.

Once soil is loosened, a large bucket is attached to the oscillating equipment and lowered into the hole. The bucket can remove a scoop of dirt able to fill a standard dump truck, Mosier said.

This process of oscillating, advancing the steel casing, and excavating continues slowly until the basalt bedrock is reached about 200 feet down. Once casing is anchored, steel caging is installed.

鈥淔or a hole that is around 200 feet deep, it is difficult to have a crane that is tall enough to lower a cage that is 200 feet into the hole,鈥� Mosier said.

So, the cages are built in sections 60 to 90 feet long. Two to three cages are needed to fill each hole, Mosier said. A crane is used to lower each section, which is then spliced with the next one.

Once the steel cages are in place, approximately 700 to 1,000 yards of concrete is poured to complete the shaft. For the first shaft completed in August, roughly 48 sensors were placed in the caging to track concrete density, said Ritch Schubert, marine operations manager at Kiewit. But none of the others will have sensors.

The project is anticipated to be complete in fall 2025.