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April 29, 2013 at 9:52 AM

Second batch of 520 pontoons floats out

pontoon batch 2

A 360-foot-long and 11,000 ton longitudinal pontoon is towed through the launch channel of the SR 520 pontoon construction site. The float-out operations coincided with the high tide late in the evening on April 28. Crews worked through blustery winds and heavy rain to float-out the six pontoons from the casting basin. (Photo / Washington State Department of Transportation)

Six Highway 520 bridge pontoons floated out of their casting basin and into Grays Harbor early Monday, taking advantage of high tide to lift the concrete structures off the basin floor.

This group consists of three lengthwise pontoons, each 360 feet long; one pontoon that will be the west endpiece of the floating bridge; and two smaller supplemental pontoons, attached to the sides to add buoyancy. They will be inspected in the harbor before being towed to Lake Washington, the state Department of Transportation says.

The large pontoons were strengthened using high tension steel cables, to compress them from the two sides before leaving the basin. This is meant to prevent a repeat of long cracks that developed in the first batch last year. Repairs and redesigns are expected to cost taxpayers tens of millions of dollars. Pontoons are being built at Grays Harbor and Tacoma under a $367 million contract.

John Reilly, head of an expert review panel, said he and fellow member Larry Kyle examined some of the work in the basin, a couple weeks ago. “Cycle II is much improved, much less cracking, less extensive in terms of structural cracks,” he said. and noticed  On the tops of the large pontoons, “the few cracks we saw were pretty small, 1 foot or shorter,” he said.  Narrow core samples have also been taken, to confirm epoxy has penetrated into the pontoon walls in places where cracks did need to be filled, Reilly said.

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