Owner San Francisco Public Utilities Commission
Lead Design Firm Jacobs Associates
Construction Manager Jacobs Engineering Group Inc.
Contractor Michels/Jay Dee/Coluccio JV
Pipeline Engineer SFPUC
MEP Engineer URS
Geotechnical Engineer Fugro West
Completed seven months ahead of schedule, the Bay Tunnel Project provides an essential water conduit underneath San Francisco Bay in an environmentally and seismically sensitive area. The 15-ft-dia, fivemile- long tunnel shaft runs 110 ft below the bay to deliver water to 2.4 million customers.
The project was the first to use a tunnel boring machine (TBM) under the bay. Construction included a 124-ft-deep diaphragm slurry-wall launch shaft with an outer diameter of 64 ft and 3-ft-thick walls. A 12-ftthick reinforced concrete tremie slab keyed into the shaft walls at the bottom. A watertight exit shaft extended 93.5 ft deep on the east side of the bay.
Without access points beyond the two shafts on either end, crews used an earth pressure balance TBM to handle a wide range of geologic and high groundwater-pressure condicontions. In addition, the lack of midpoint access required the assembly of a conveyor system more than 10 miles long to remove tunnel spoils.
The project team tightly controlled cost change orders and implemented seven major initiatives that saved $12.7 million. One initiative led to the use of ground-freezing technology for the exit shaft, which not only saved money, but reduced risk of water intrusion and prevented damage to the surrounding fragile marshland ecosystem.