page_title: Eastern span replacement of the San Francisco–Oakland Bay Bridge
section_title: Skyway Viaduct
hierarchical_section_title: Eastern span replacement of the San Francisco–Oakland Bay Bridge / Design and construction / Skyway Viaduct
caption_attribution_description: English: New Eastern span of the San Francisco-Oakland Bay Bridge as of 29 May 2008.
context_page_description: The eastern span replacement of the San Francisco–Oakland Bay Bridge was a construction project to replace a seismically unsound portion of the Bay Bridge with a new self-anchored suspension bridge and a pair of viaducts. The bridge is in the U.S. state of California and crosses the San Francisco Bay between Yerba Buena Island and Oakland. The span replacement took place between 2002 and 2013, and is the most expensive public works project in California history, with a final price tag of $6.5 billion, a 2,500% cost overrun from the original estimate of $250 million. Originally scheduled to open in 2007, several problems delayed the opening until September 2, 2013. With a width of 258.33 ft, comprising 10 general-purpose lanes, it is the world's widest bridge according to Guinness World Records.
  The Bay Bridge has two major sections: the western suspension spans and their approach structures between San Francisco and Yerba Buena Island and the structures between YBI and the eastern terminus in Oakland. The original eastern section was composed of a double balanced cantilever span, five through-truss spans, and a truss causeway.
context_section_description: The skyway viaduct connects the SAS portion of the bridge with the Oakland shore. By 2007, 75 percent of the skyway portion was completed. Since this section crosses the shallower portion of the bay, the foundations were constructed within sheet-pile cofferdams. By mid-2009, the final connection of the viaduct portion with ground level at the eastern end was being finished and the pedestrian walkway was being attached to the completed sections.
  Rather than set pilings deep enough to reach bedrock, the pilings are founded in firm archaic mud below the soft mud deposited by distant placer mining in the late 19th century. Since even the archaic mud is too weak in this concentrated load application for conventional vertical friction piles, large diameter tubular piles were driven (inside the pumped-dry cofferdams) at angles, forming a "battered" (splayed) footing, through the archaic mud into the firm aggregated sand, mud, and gravel of the Alameda formation. Where long pilings were needed, segments were welded together as completed segments were installed.
  When all pilings were in place, a reinforced concrete pad was poured at the bottom of the cofferdam to form a footing for the column, subsequently cast in place around rebar using reusable metal formwork.
  A single viaduct segment located over each column was cast in place using forms. Pairs of precast span segments, fabricated in Stockton, were barged to the location and lifted into place with a specialized cantilever lift. (Cantilever lifts, counterweights and other equipment and materials were lifted either by a barge crane or by a jack-up crane located between adjacent columns.) Once in the proper location, the opposing segments could then be joined with through tendons (cables within conduits that are tensioned with jacks), forming a balanced cantilever over the column. Eventually, the gap in spans between columns was closed, forming a tendon-reinforced beam.
  The Oakland Touchdown is a curved elevated roadway that connects the skyway to the Oakland shore (the beginning of the bridge). The curve is required to bring the alignment to that of the existing ground-level approach road. Like the Yerba Buena Island Transition Structure (YBITS) to the west of the main span, this section is also an end segment of the new bridge and is being constructed at the same pace as the YBITS. The construction process consists of two phases, the first phase already completed (westbound traffic side). The eastbound touchdown could not be completed until the existing roadway was out of the way. This was done by constructing a gentle swing to the south so that the touchdown may be completed. The first stage of this work was to move the eastbound traffic to the south was completed with only minor traffic delays during the 2011 Memorial Day holiday (May 28–30). The driving experience has been improved, without the problems that came with the infamous S-curve. A second stage to move the westbound traffic into the space made available required the construction of an elevated approach. This was completed on February 19, 2012. This recently designed procedure is expected to save time in the total effort, speeding the completion of the span. The Oakland Touchdown was completed in March 2013.
  On the three-day weekend beginning 8:00 PM Friday, February 17, 2012, the westbound lanes were shut down to allow the connection of the approach roadbed with the new temporary structure. The execution of this task was dependent upon weather, dry conditions being required for re-striping the lanes, and it was not determined until a few days before that the work would be done on this weekend. Originally scheduled for completion by 5 A.M. on Tuesday, February 21, the work was completed 34 hours ahead of schedule, and opened to traffic at approximately 7:15 P.M. on Sunday, February 19.
caption: New and old approach spans (May 2008)
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