Saturday morning, Nov. 16, 2013, at 4:10 a.m. the first vehicles drove through the new, two-lane, 3300-ft long Fourth Bore of the Caldecott Tunnel. The long-planned $417 million project provides congestion relief along SR 24 to residents and workers in the East Bay, and brings to an end the daily process of switching the traffic direction of the third bore to accommodate travel between Alameda and Contra Costa counties.
The new Fourth Bore features wide travel lanes, roadway shoulders, bright lighting, emergency exits along the length of the tunnel, and state-of-the-art fire and life safety systems. The tunnel’s incident detection and response systems underwent extensive testing before Caltrans began the traffic realignment needed for the new SR 24 lane configuration utilizing the Fourth Bore.
Construction began in January 2010 by contractor Tutor-Saliba Corp. The fourth tunnel parallels the existing third tunnel and has seven interconnecting personnel passageways to facilitate maintenance and emergency access.
The fourth bore tunnel was being constructed by the sequential excavation method (SEM), which provides the required flexibility to construct a wide-span tunnel in weak and variable ground conditions. The sequential excavation was performed by roadheader, with pre-support measures ranging from spiling to pipe canopies. A waterproof membrane was placed on the inside face of the initial support – a mix of reinforced shotcrete, lattice girders and rock bolts, followed by the construction of a cast-in-place reinforced concrete lining.