Building a bridge is a long, complex and expensive undertaking. With construction now underway on three bridges in the Bay Area, the California Department of Transportation (Caltrans) and the Metropolitan Transportation Commission (MTC), acting as the Bay Area Toll Authority, have been confronted with a variety of problems, ranging from a lengthy design process for the new East Span of the San Francisco-Oakland Bay Bridge to protection for endangered fish at the Martinez-Benicia bridge construction site.
Unfortunately, delays for construction projects usually add to costs. This was certainly true for the Bay Bridge, where the extended design process may have been a factor in raising the cost to $2.6 billion. For the Benicia-Martinez Bridge, delays imposed by fish protection requirements threatened to send the project back to the drawing boards, or at least swallow money which had originally been allocated to other projects in the region.
In 1995, the total cost of the Benicia-Martinez Bridge was estimated at $286.4 million. The cost escalated due to a redesign to meet Coast Guard requirements, updated seismic analysis, more railroad crossings and changes at the northern end to satisfy concerns of the San Francisco Bay Conservation and Development Commission. Boosted by a strong economy, bids came in well above estimates, and in September 2001, Kiewit Pacific Company was awarded a $286.6 million contract for the main span of the bridge, with additional contracts needed for interchanges and approaches.
Other engineering problems were also encountered, but the greatest stumbling block became apparent in Spring 2002, when dead fish were discovered after a round of pile-driving. Many of the fish which swim through the Carquinez Strait and pass under the Benicia-Martinez Bridge are endangered or threatened species, including striped bass, salmon and steelhead, sturgeon, Delta smelt and Sacramento splittail. Other work on the bridge continued, but pile-driving was immediately discontinued while Caltrans consulted with the National Marine Fisheries Service and the California Department of Fish and Game.
Unlike the new span of the Carquinez Bridge, which is a suspension bridge (the first to be built in the Bay Area in decades), the Benicia-Martinez Bridge's second span will be supported by almost 75 deep-water piles and additional piles in shallow water at each end. The deep-water piles are 160 feet long and eight feet in diameter and must be pounded through mud into bedrock by hydraulic hammers. Each blow may move the pile only a fraction of an inch but creates 200 decibels of noise, which radiates outward in a shockwave which can be lethal to fish nearby. Fish rely on air in swim bladders to position themselves in the water, but the pressure in the bladders can be affected by shockwaves and burst the bladders, killing the fish.
Caltrans had developed a technique, using a "curtain" of air bubbles to absorb the shockwaves, to protect fish near construction for the new Bay Bridge span. However, because of differences in the areas around the two bridges, the air bubbles were not as effective at the Benicia-Martinez site. Caltrans began to experiment with variations, including one that held the air bubbles between the piles and a metal sleeve. This was cumbersome and expensive to use, and could have added $164-$300 million to the cost of the bridge if used for all pile-driving.
Meanwhile, resource agencies proposed to limit pile-driving to times of the year when the endangered species were not migrating in large numbers through the area, or to periods of slack tides when fish were not moving around.
By January 2003, it was clear that unless Caltrans and its contractors could find an solution which was both cost-effective and acceptable to the resource agencies, piles would not be in place by Fall 2003, an essential milestone for completing the bridge. With delay costing thousands of dollars per day, other projects to be funded from toll revenues were in jeopardy. These included deck rehabilitation on the Richmond-San Rafael Bridge, and a new Interstate 880-Highway 92 interchange.
In late January, Caltrans began testing a new version of the bubble curtain, generated by a cage of pipes around the piles. Underwater sound tests measuring decibel levels were satisfactory; regulatory agencies extended the pile-driving permit, which was set to expire at the end of February to protect fish as they began to migrate in March. The remaining piles should be in place within three to six months. The bubble curtain technique promises to be useful for the seismic retrofit on the Richmond-San Rafael Bridge, as well as the new Bay Bridge span.
A new timetable and financial picture are taking shape for the Benicia-Martinez Bridge. The revised opening date for the bridge has now moved from December 2004 to December 2005, and the projected total cost is now $570 million for the bridge, a new toll plaza and related interchanges, with some estimates putting it as high as $900 million. While the high estimate may not be realized unless some new problem arises, MTC is considering resources to pay for the increased costs which have already been incurred, and hoping to avoid similar problems on the other bridge construction projects.
Leslie Stewart
For more information:
Rod McMillan, MTC, 510-817-3260; rmcmillan@mtc.ca.gov
Greg Bayol, Caltrans, 510-286-6169