Work is nearing completion on several portions of the Benicia-Martinez Bridge seismic retrofit in Northern California. Crews from the FCI Constructors and Interbeton Inc. joint venture are finishing up cast-in-drilled-hole construction and grouted-pipe piling on the last of nine footings. In addition, wall and column pours to strengthen the piers are progressing across the Carquinez Strait. Retrofits of steel trusses will be wrapping up this fall.
All construction materials have been supplied from barges working at high tide to avoid harming ecologically sensitive wetlands. As many as 13 barges a day must negotiate swift currents in both directions through the narrow channel, and must navigate around oil tanker traffic. Workers on the pier footings work from barges, while those retrofitting the steel trusses must tramp along a catwalk beneath the bridge deck.
Approximately 3 million pounds of structural steel and about 12 million pounds of rebar have been added to strengthen the bridge. Debris from the 17 holes drilled into each concrete pier footing was dumped onto barges and ferried up the Sacramento River to a landfill. About 48 miles of soil and rock have been drilled.
In late August, crews began work on the seismic isolation bearings and expansion joints. The bearings are the largest friction pendulum bearings ever built, weighing over 40,000 pounds each. Joint venture crews are raising the bridge up to 1 foot, 1/4 inch at 22 locations to accommodate the bearing replacement. Workers are using masonry saws to remove the concrete catcher blocks of the existing bearings, which are located at the tops of the concrete piers, directly under the roadway trusses. Hydraulic jacks are then used to hold up the bridge and all its traffic. The old bearings are cut out with an oxygen lance, the new bearings are installed, and the bridge is lowered back onto them. The bearings are 13 feet in diameter, and have a lateral displacement capacity of 53 inches. Their design bridge weight plus traffic weight load is 5 million pounds.
In addition, after retrofitting the bearings at piers 3 and 13, joint venture crews will begin retrofitting the expansion joints. This will consist of demolishing the old concrete expansion joints and replacing them with steel and elastomeric concrete.
The retrofit of the 6,156-foot-long Benicia Martinez Bridge is scheduled for completion in April of 2001, with the exception of significant change-order work in the footings and walls at piers 3 and 13. The bridge carries 6 lanes of traffic, averaging 100,000 vehicles a day. It is one of the largest bridges to date to be seismically retrofitted.