Paula Wallis, TunnelTalk

Four very close bids came in yesterday, November 11, to build the first ever tunnel under the San Francisco Bay in Northern California. All of the bids were well under the Engineer's estimate, and a mere $97 thousand separates the two lowest bidders as contractors compete for a backlog of projects to see them through uncertain economic times.

Fig 1. Bay Tunnel alignment

The numbers are still being verified, but unofficially Michels/ Jay Dee/Coluccio JV is the apparent low bidder with a bid of $215.3 million, narrowly undercutting Obayashi/Kenny JV's bid of $215.4. Traylor/Shea JV submitted a bit of $224.7 million followed by Flat Iron West with a bid of $245.6 million.

The lowest bid is almost $35 million below the Engineer's estimate of $250 million. Like many owners with secure revenue sources, the San Francisco Public Utilities Commission (SFP?UC) is benefiting from the economic downturn. So far the commission has saved more than $100 million on 10 contracts associated with its $4.2 billion water system improvement program or WSIP, including the Bay Tunnel.

"We are happy with the level of interest on the Bay Tunnel and the number of bids received," said Johanna Wong, Project Manager for the SFPUC. Wong said another major tunneling project in the Bay Area delayed the bid opening for the Bay Tunnel. "Many of the contractors were also bidding on the 4th bore of the Caldecott Tunnel in the East Bay for the California Transportation Department," said Wong. "When Caldecott was postponed, all the bidders requested an extention on the Bay Tunnel deadline as they were all too busy working on the Caldecott bids that were due September 29." Michels/ Jay Dee/Coluccio JV did not bid on Caldecott. The apparent low bidder for that contact is Tutor Saliba with a bid of $215 million, which is about 20% below the Engineer's estimate.

Last month Jay Dee/Coluccio/Michels, JV was awarded the second tunneling contract for the 3.15 mile (5km) University Link (U-Link) light rail system in Seattle. The JV's bid of $153.5 million was about 12% below Sound Transit's original cost estimate for the project. Jay Dee/Coluccio/Taisei JV also holds the West Tunnel contract for Seattle's $1.8 billion Brightwater conveyance tunnel.

Fig 1. Three tunnels and other elements of the SFPUB's $4.2 billion Water System Improvement Program

The Bay Tunnel is one of three major tunneling projects for the SFPUC. On Tuesday, November 10, the Commission approved the New Irvington Tunnel Project to construct a new 3.5 mile long tunnel parallel to the existing tunnel between the Sunol Valley south of Highway I-680 and Fremont, California. With funding secure that bid process is schedule to begin November 17.

The third major tunneling project is already under construction. Shank/Balfour Beatty JV was awarded the Crystal Springs Bypass Tunnel in October 2008 with a bid of $55.7 million. In early October 2009, the newly assembled TBM was lowered approximately 155ft into the south shaft to begin excavating the 4,200ft long tunnel on the San Francisco Peninsular.

Crystal Springs Tunnel TBM

The Bay Tunnel will extend under the San Francisco Bay south of the Dumbarton Bridge, from East Palo Alto to Union City on the East side of the bay (Fig. 1). With only one access shaft at either end of the 5-mile x 9ft (8km x 3m) diameter tunnel, access will be a major challenge along the alignment that will reach depths ranging from 75ft to 110ft (22-33m). EPB excavation is specified for the drive in mostly sandy and silty clays. A section of Franciscan bedrock near the end of the drive will require outfitting the TBM with disk cutters for the final push to the eastern shaft. Jacobs Associates designed the Bay Tunnel and Jacobs Engineering was awarded the construction management contract.

Two of California's largest active faults, the San Andreas and the Hayward, border the tunnels general route. Given the seismic activity in the Bay Area, tunnels, which are more resistant to earthquake damage and provide less surface disruption than pipelines or immersed tubes, are generally preferred. However, BART's Transbay Tube, built in the 1960's, is still one of the longest immersed tubes in the world, and it survived the devastating 1989 Loma Prieta Earthquake without damage.

Still, environmental considerations also dictate the construction method. A bored tunnel will avoid environmentally sensitive habitats and surrounding salt marshes. Current inspection and maintenance on the existing pipeline crossing built on a system of trestles more than 70 years ago is difficult. Access is denied six months out of the year in these sensitive habits that host over 280 species of migratory birds, and are home to the endangered California clapper rail and salt marsh harvest mouse.

Construction on the Bay Tunnel is schedule to begin early next year.

References

Water tunnels to recharge aging system - TunnelTalk, Sept 2009
Bay tunnel (video) - TunnelTalk, March 2008
Crystal Springs Tunnel awarded - TunnelTalk, October 2008

SFPUC