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Foundation construction underway for new Sellwood Bridge

by: DAVID F. ASHTON - Although planked with wooden beams, this work bridge is sturdy enough to support a massive crane. The vertical rails installed on the old pier will support a water saw that will cut it into pieces.With little publicity, the very quiet blasting near the west-side approach of the new Sellwood Bridge, reported on in the last issue of THE BEE, ended in April.

But, activity has picked up considerably in the east end, just north of the Sellwood Harbor Condominiums. Multnomah County project spokesman Mike Pullen told THE BEE. “Contractors are starting to build the foundations for the new eastern approach.”

The old bridge’s approach, Pullen pointed out, was supported by many vertical columns. “The new bridge will only have about four columns in this area, and will have longer spans. It will open up a more efficient use of space for Sellwood Harbor after the construction has been completed.”

Standing on the south side of the bridge’s east-end approach, Pullen pointed out a huge steel casting – it looked like a metallic circle – in the ground, near the railroad tracks.

“A contractor used machinery to vibrate this casing into the soil,” Pullen said. “The vibration was so intense, people could feel it in our project office blocks away. The impact on the ground was substantial.”

Further to the west, contractors were using a different method to slip a steel casing into the ground.

A huge machine grasped the casing, and slowly rotated the steel cylinder about 30° in one direction, stopped, and then slowly rotated 30° back in the other direction. The machine kept ratcheting constant downward pressure, causing the casing to eat its way down into the earth – this time, with no vibration.

At the same time, a huge ball-shaped excavator reached down in the casing, removing a half-dump-truck load of dirt with every mighty scoop.

“When the casings have been sunk down to bedrock, contractors will lower steel rebar cages into the casings, and they’ll be filled with concrete,” Pullen pointed out. “Putting in these foundations will progress from east to west.”

Walking into the worksite, next to the river, the enormity of the east side “work bridge” – built just south of the old bridge – became apparent. From a distance, it appeared as if the work bridge was decked with wooden 4x4s. A closer inspection reveals the decking to be comprised of much bigger 12” x 12” wooden beams.

When we looked up and eastward, another crew was busy, sinking smaller foundations to install a shoring wall for the column that will be closest to the river.

Contractors are scheduled to begin removing the old Sellwood Bridge bents, or concrete piers, in the river. Special “tracks” have already been installed on one of the bents, on which a “water saw” will ride, as it slices the piers into manageable-sized chunks that can be hoisted into barges.

“It looks like that work will begin in May,” Pullen said. When the work has been completed, the piers will be removed down to the mud line of the river, he added.

Keep up-to-date with the process of this monumental project through Multnomah County’s dedicated website – it includes two live web cams – at www.sellwoodbridge.org