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Concrete Mishap Spurs Bridge Work Redo

Wednesday, December 19, 2012

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A brand-new bridge pillar on a highway project will be destroyed and rebuilt because the component's exterior is too thin, the Washington State Department of Transportation (WSDOT) has reported.

The issue is the latest to bedevil progress on the SR 520 bridge over Lake Washington—a project that has already been plagued by cracks, leaks, and spalling during construction of massive concrete pontoons.

In January 2011, WSDOT awarded a $586 million design-build contract to Kiewit-General-Mason Joint Venture to build the concrete pontoons and a six-lane bridge, among other things.

Once completed, the SR 520 bridge roadway will provide a seamless transition from the floating bridge to fixed bridges off the shore and on land, connecting Seattle and Medina.

Photos: WSDOT

One of 10 recently built pillars will be destroyed and rebuilt after the concrete was found to be too thin.

The flawed column is one of 10 poured this fall. The columns were formed by pouring concrete around a cylindrical cage or reinforcing bar contained in a temporary steel tube.

When the tube was removed from the one column, some of the concrete peeled off with it, and workers found that the rebar cage had shifted during the pour, leaving less than the normal 1.5-inch concrete thickness around the rebar, said Suanne Pelley, WSDOT spokeswoman.

"KGM's decision to replace this column at their expense is the appropriate action," said Julie Meredith, the SR 520 program director. "KGM is implementing the quality assurance program that is a key component of our contract."

Concrete Failed Quality Specs

On Friday (Dec. 14), WSDOT issued a quality assurance update that said crews were removing and replacing one of the 10 concrete columns where the concrete pour failed to meet quality specifications.

The new roadway deck will be installed on top of bridge piers before sloping down onto the columns being constructed on the pontoons. In October, the crews began construction on 10 58-foot-tall concrete columns on top of Pontoon W, one of two cross pontoons.

The SR 520 bridge is nearing the end of its original life and has become vulnerable to windstorms and earthquakes.

KGM inspectors discovered that one of the concrete columns had too little buffer between the outer layer of concrete and the reinforcing steel inside.

KGM project managers then determined that the column should be removed and replaced to meet the quality requirements. The column will be removed and dismantled, and the concrete and steel rebar will be recycled, WSDOT said.

'Cracking Happens'

In late November, crews completed construction of 345 pre-cast concrete wall panels; KGM rejected nine of these panels. Three exceeded the contractual limits for cracking, and six were rejected due to a duct alignment issue, WSDOT reported in an update.

The nine panels had not yet been installed inside the pontoons.

"Early detection of these panel issues shows that the established quality assurance process is working," said Meredith. "Inspections of all concrete will continue as the construction proceeds. We know that with concrete, cracking happens."

Meredith said the contract specified when concrete must be replaced or repaired.

"The safety of travelers is always our first priority, and we are addressing all of the challenges that occur in a construction project," Meredith said.

Continued Work

Earlier this fall, crews used heavy machinery to drive massive, interlocking steel sheets into the lakebed, creating a cofferdam to section off a 170-foot-long by 50-foot-wide by 40-foot deep area in Lake Washington. Crews will pump approximately 2.5 million gallons of water out of this area.

Once the cofferdam is drained, crews will excavate into the lakebed and start construction on the new bridge pier. This is the last of three piers that will connect the land-based highway on the eastside to the new floating bridge currently under construction.

Crews are pumping 2.5 million gallons of water out of a cofferdam in Lake Washington to start construction on a new bridge pier.

Replacing a Vulnerable Bridge

The SR 520 bridge sees 115,000 cars per day and has only two lanes in each direction. After nearly 50 years in service, it is nearing the end of its original service life. The bridge's pontoons have become vulnerable to windstorms, and its support columns have become vulnerable to earthquakes.

The new pontoons are designed for a 75-year service life to withstand windstorms up to 89 mph and a 1,000-year earthquake event. The new bridge will provide a six-lane roadway.

This project is the first construction phase of the SR 520 – I-5 to Medina: Bridge Replacement and HOV Project, for which the Washington Stage Legislature has set a program budget of $4.65 billion.

According to WSDOT, the latest jobs report counted 832 jobs directly connected to the pontoon and floating bridge project sites.


Tagged categories: Bridges; Concrete; Concrete defects; Construction; Cracks; Design; Government contracts; Inspection; Quality control

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