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Troublesome shaft successfully sunk in river, at last

SELLWOOD BRIDGE UPDATE


by: DAVID F. ASHTON - This is a column capped beam that will support the new side bridge deck, before it lands upon the now-completed Eastern Abutment, seen in the background.Sellwood Bridge construction workers and engineers were stumped for a while this summer, trying to drill for one of the four columns that will support Bent 5, just east of the Willamette River’s center.

“They’ve tried sinking this shaft twice before,” said Multnomah County Sellwood Bridge Project Manager Chuck Maggio, looking up at the steel casing at the end of the eastern work bridge.

“They abandoned drilling it twice, because obstructions damaged the steel casing. While they worked to solve this problem, they sank the other three shafts,” Maggio told THE BEE.

Ultimately, their fix was to mount smaller “teeth” on the end of the steel casing that is used to grind the shaft down through the mud – and through the 80-year-old construction debris, and rock formations. “It’s kind of like changing out the blades of a saw.”

The other strategy suggested by their contractor, the Malcolm Drilling Company, Inc., was to put less downward pressure on the casing. “They also suggested rotating the casing in only one direction, instead of using the typical back-and-forth oscillation drilling.”

The plan worked. “That’s why Malcolm has become a leader in the field of oscillation drilling,” Maggio said.

“As our ‘in-water work window’ closes, successfully drilling this shaft was very good news,” commented Multnomah County spokesman Mike Pullen. “We are seeking permission, after the in-water period ends at the end of October, to do some additional work.

“If the permit is approved, contractors will be able to lower a ‘perched box casing’ – it connects the four columns to the bridge’s arch – into the water. It’s not the same as drilling; it doesn’t affect the river’s bottom or the fish,” Pullen added.

The new traffic change at the west end interchange, prohibiting a southbound turn on Hwy. 43, seemed to confound unaware drivers for the first week or so, Pullen observed. “Now, it seems that most drivers know they need to drive north, and make the turn-around to go south – or use another bridge.”