Gov. Arnold Schwarzenegger's plan to save hundreds of millions of dollars and speed construction of the new Bay Bridge by replacing the single- tower suspension design with a concrete skyway may not be so simple after all.
A plain concrete causeway is less complex than a suspension bridge, but it has its own difficulties and plenty of unknowns. The state has already discovered some of the pitfalls on the skyway section of the eastern span now under construction, which documents show is beset by huge cost overruns.
Caltrans also has been plagued by overruns on the new Benicia Bridge -- another concrete skyway.
In making the administration's case to the state Senate last week for building the skyway, Will Kempton, director of the Transportation Department, argued that the concrete viaduct is "a real simple structure'' and something with which Caltrans engineers are familiar.
"We have the experience of 1.3 miles of skyway construction going on just east,'' Kempton said. "This project will be similar to that project.''
But Caltrans figures show that the cost of the twin concrete viaducts now under construction is projected to soar 55 percent over the $1.04 billion contract awarded to Kiewit-FCI-Manson in 2002. The final price tag will be 62 percent more than Caltrans first estimated in 2001, the documents show.
"Can you believe that?'' said state Sen. Tom Torlakson, D-Antioch, a critic of the governor's skyway proposal. "That's a pretty huge off the mark.''
The threat of complications, and the delays and cost overruns they would bring, could erode support in the Legislature for Schwarzenegger's skyway plan. The administration's pitch has been that switching designs would shave $300 million to $500 million from the $5.3 billion cost of the eastern span and enable the state to finish the bridge by 2012 -- as quickly as the single- tower suspension span, which is fully designed and ready to build.
Caltrans officials blame the skyway overruns on a variety of problems, including higher-than-expected costs for cement and steel, and increased overhead expenses for both the contractor and the state.
The state has encountered a different set of problems on the other major span being built as a concrete skyway, the new Benicia-Martinez Bridge. But the effect has been the same -- the cost of the five-lane bridge parallel to the existing span on Interstate 680 has soared to $1.1 billion, about $405 million over 2001 estimates and almost four times Caltrans' original 1985 estimate of $286 million.
Those overruns, Caltrans officials said, were the result of an unanticipated threat to fish, the unforeseen discovery of weak rock requiring innovative drilling methods, and difficulty in finding building materials that fit the design of the bridge.
Some of the same underwater uncertainties would face any engineer trying to design and build an extension of a Bay Bridge concrete skyway to Yerba Buena Island.
The project would require construction of two or three additional foundations in a particularly deep, mucky part of the bay where soil conditions aren't entirely known. They could encounter unpleasant geological surprises, said engineers, architects and bridge construction experts.
"It's probably the toughest area of the bay to build foundations,'' said one Bay Area bridge engineer, who requested anonymity out of fear of losing business from the state.
The suspension span that Schwarzenegger wants to dump would require a large single foundation to support its tower. But it faces far fewer uncertainties, because geotechnical tests have been completed and construction was under way when the governor proposed his switch. The work has since been halted.
Caltrans has drilled "a significant amount'' of soil samples in the area to prepare for possible skyway construction, Kempton told the Senate Transportation and Housing Committee. But he acknowledged that much more geotechnical work needs to be done.
"They don't even know what's down there yet,'' said an international construction engineer, who also requested anonymity for fear of losing work opportunities. "You'll have one surprise after another, and you won't end up saving any money."
Robert Luffy, president of American Bridge, part of the consortium that turned in the lone bid on the single-tower suspension span that Schwarzenegger is trying to drop, said the uncertainties and difficulties of building in the bay are what is really driven bridge costs skyward.
"What's being missed here is the lack of realization of the site,'' he told the Senate committee. "It's not the design that's so unusual -- it's the site.''
Part of what makes the site unusual is the need to avoid blocking a deep- water shipping channel just east of Yerba Buena Island. Adding foundations and columns for the bridge will squeeze the channel and require careful placement of the foundations, engineers say.
It could also require construction of one segment of bridge deck reaching more than 700 feet between columns. And that's stretching the limits of concrete construction, engineers say, especially in a seismically unstable area.
Concrete spans are heavy and require larger support columns to make them stable. That increases costs and gives the segment of the bridge a bulky look.
Changing the design of the final 2,000 feet of the bridge also would require new seismic studies and modifications to the points where the new section of concrete viaduct would connect to the portion now under construction, and where it joins the approach to Yerba Buena Island.
"This is not a simple case of mix and match,'' said Ephraim Hirsch, a San Francisco civil engineer.
Kempton disagrees with such concerns, and still says the skyway is the best choice. "We have to move quickly,'' he said at the committee hearing, "and we believe the skyway offers the best option to build a safe bridge in a reasonable time at the lowest cost.''
E-mail Michael Cabanatuan at [email protected]. |
