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Shaft-sinking snagged, as Sellwood Bridge in-water work begins

by: DAVID F. ASHTON - A worker positions steel rebar, temporarily held in place by a crane, to be formed into part of a cage to give strength to the river piers of the new Sellwood Bridge.Construction of the new Sellwood Bridge hit a snag in mid-July, preventing a continuous concrete pour for the first pier shaft at Bent 5, located just east of midpoint in the Willamette River.

Instead of just pounding it in, a giant oscillation-drilling machine slowly rotates a steel casing, edged with carbide-tipped cutters, easing it through the river bottom muck down to bedrock.

“Near what should be the bottom of this shaft, is something harder than steel,” explained Multnomah County Sellwood Bridge spokesman Mike Pullen. “It is breaking and bending the shaft casing; it could be a boulder.”

Although the contractor was within a foot of the bottom, specialists didn’t believe they had a solid base, because the material was crumbling, Pullen added. “They want to make sure they are down to bedrock.”

On the way down, contractors found remnants from the original bridge’s construction, such as large beams and timbers. “Encased in the mud, they stayed preserved, in good condition,” Pullen revealed.

While experts tried, quite literally, to get to the bottom of the problem in the first shaft, contractors moved over and started sinking the second of four shafts that will support Bent 5 of the new bridge.

Meanwhile, two old bridge concrete piers have disappeared below the water line, cut up into 100,000 pound chunks, and barged away. Below the surface, divers continue to cut away at the old bents until the foundations are below the mud line of the river.

During an on-site tour for THE BEE, Pullen pointed out workers welding double-walled rebar “cages” that will be lowered into the pier shafts, once they are down to bedrock, to reinforce the concrete poured into the casings.

Also visible on the east side is the rebar structure – the bridge’s abutment – that will secure the bridge to land, and stabilize the hillside.

And, with the start of their “in-water work season” that runs from July 10 until October 15, contractors are hard at work pounding pilings into the riverbed to form the base of the west-side work bridge.

“Even with the difficulties, the project remains on schedule,” Pullen said.


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