‘Retrofit by Replacement’

West Approach to the Bay Bridge Opens

By Greg Aragon

How can a contractor replace a mile of roadway within its own footprint, while at the same time keeping 280,000 daily drivers moving?

“Very carefully, with constant coordination and meetings,” says Fred Morell, whose company, Tutor Saliba Corp. of Sylmar, this month finished the $450-million West Approach Project in San Francisco.

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As project manager, Morell oversaw the “retrofit by replacement” of a 1-mi stretch of Interstate 80 linking downtown San Francisco to the historic San Francisco-Oakland Bay Bridge. The project, delineated by Fifth Street and the bridge anchorage on Beale Street, included the replacement of six on- and off-ramps, as well as the double-deck roadways from Third Street to the an­chorage so that each deck will have independent columns and foundations.

“It was close quarters,” Morell says. “We were so close at times that we could reach out and touch existing buildings, not to mention that there were three active city streets that we crossed over that had to be open at all times.”

To overcome proximity issues, Tutor-Saliba, along with Caltrans, utilized a “retrofit by replacement” method in which the project was performed in a series of six elaborate stages. This included lane shifts, regular lane and ramp closures, and one partial bridge closure.

“The project was done in multiple stages in order to maintain the same number of lanes during weekly commute hours,” says Deanna Vilcheck, resident engineer for Caltrans.

Each stage involved the construction of a temporary structure upon which vehicles were rerouted. The old structure was then demolished and work began on the new structure in the original footprint. Drivers were rerouted back onto the completed replacement structure, and the temporary structure was demolished.

In all, crews used 14 million lbs of steel to build 25 temporary structures.  

Morell says the toughest part about getting both temporary and permanent structures up was getting foundation piles driven into varied soil conditions.

“We drilled into anything from soupy muck to very hard rock,” he says. “We had everything imaginable in the foundations on this project.”

He adds that as they got closer to the bay, such as on top of Rincon Hill, the ground was so hard they had to core down 80 ft through rock to get the piles placed.

And when they moved away from the water toward San Francisco, workers had to use friction piles because the bay mud was so deep they couldn’t reach bedrock.

“So we drilled a temporary case into the soupy bay mud and then built the pile inside of that,” he adds.  

Work on the 72-year-old I-80 structure began in 2003. The project, designed by Caltrans, is one of a series of seismic safety projects totaling more than $6 billion that will completely reinforce the historic 8-mi-long Bay Bridge.

Looking back on the five-year, nine-month job, Morell says he is most fascinated by the free-resting design of the bridge deck, which is unconventional for Caltrans.

“This structure is different from any other structure I’ve built,” he adds. “In typical [bridge] construction there is rebar that extends from the column up into the bent cap structure to resist the earthquake forces.”

But on this project, he says the roadway deck sits on top of piles and columns with pins on top of each column.

“[The bridge] is not connected in any fashion with rebar; it just sits up there,” Morell says. “And in the computer model it is able to move and rotate and flex substantially more than a traditional structure.”