November 8, 2007 By Tamara Warta
The San Francisco-Oakland Bay Bridge is a vital artery for Northern California commuters, carrying nearly 300,000 vehicles per day. So closing the span for seismic upgrades presented state transportation officials with perhaps the ultimate high-profile and high-pressure project.
The California Department of Transportation (Caltrans), working with a team of private contractors, devised a plan to demolish a 350-foot stretch of roadway and slide a new, seismically strengthened piece of road in its place using a series of computer-controlled hydraulic jacks. The work needed to be done entirely over the three-day Labor Day weekend, with the bridge returning to service in time for commuters to return to work on Tuesday morning.
Following a carefully choreographed process, Caltrans and the California Highway Patrol closed the bridge at 8 p.m. on Friday Aug. 31. Work was completed by 6 p.m. Monday, Sept. 3 -- 11 hours ahead of schedule.
"We're tremendously proud to be able to open the bridge early," said Caltrans Director Will Kempton, in a statement released after the project's completion. Besides replacing the roadway, located on what's known as the Yerba Buena portion of the bridge, the project included installation of improved signs, alerts and electronic toll collection booths. The entire procedure cost around $40 million and is only phase one in a handful of planned improvement initiatives.
Caltrans worked with C.C. Myers, a Sacramento, Calif.-based construction firm, which in turn hired several subcontractors to help with the planning and demolition stages of the weekend project. Mammoet, a Dutch firm specializing in heavy lifting projects, devised the method for sliding a new, pre-constructed section of road into the cleared out portion of highway.
The new section of roadway was built months in advance of the project and was situated east of Yerba Buena Island, which is at the center point of the bridge, until traffic was cleared from the span. Sixteen computer-controlled hydraulics, known as a skid jacking system, were mounted beneath the 6,700-ton section of new roadway, which needed to be lifted and moved approximately 100 feet into place.
With such a vital bridge being taken out of commission, time and coordination were of the essence. The majority of the 70-hour project was devoted to demolition of the old roadway, which was handled by Silverado Contractors, a demolition company based in Oakland, Calif. Once demolition was finished, Mammoet's skid jacking system eased the new road into place.
"Installation of the rail system on the lower deck of the bridge went simultaneous with the final portions of demolition, and the actual move of the structure took only two hours -- and was estimated to take five," said Caltrans spokesman Bart Ney.
Mammoet's proprietary system was particularly attractive to Caltrans due to its ability to both push and pull hydraulically. "Since this type of operation is not common, it takes a company with worldwide experience to perfect it," Ney said.
Tracks were placed along the lower level of the double-decked bridge, and the new roadway was rolled into place using the hydraulics. The computer-driven moving system is modular, so it can be shipped from site to site. According to Ney, it took a little less than a week to set up the system for the Bay Bridge project, followed by two days of testing.
Getting the Word Out
How did Caltrans retrofit the bridge without triggering massive gridlock, especially during a busy holiday weekend that included Oakland A's baseball games and the season opener for UC Berkeley's football team?
Warning drivers of the bridge closure posed almost as big a challenge as the seismic upgrades themselves, according to agency officials. Caltrans started by alerting commuters through electronic traffic-condition signs, providing routine reminders to motorists months ahead of the scheduled Aug. 31 shutdown