Claremont Tunnel Seismic Upgrade

This 80-year-old tunnel crossing the Hayward fault in the San Francisco Bay Area is 18,065 feet (5,506 m) long and 9 feet (2.7 m) in diameter. It carries up to 175 million gallons per day of treated water to more than 800,000 residents. After the magnitude-6.9 Loma Prieta earthquake in 1989, owner/operator East Bay Municipal Utility District identified the Claremont Tunnel as its key facility requiring seismic upgrades.

Jacobs Associates served as prime consultant, leading a dream team of tunneling experts that identified engineering alternatives and completed final design. During construction, Jacobs Associates also provided construction management support, resident engineering, and inspection services.

The team decided to renovate the existing tunnel and construct a bypass tunnel to reroute water through the primary and secondary Hayward fault zones. The geology consists of sheared to intact sedimentary, volcanic and metamorphic rocks, including mélange. The design is the first of its kind. An expanded vault section across the fault accommodates up to 8.5 feet (2.6 m) of lateral offset without water-flow interruption. Steel set and rebar reinforcing around the shotcrete- and concrete-lined vault is designed to curve like a spine during an earthquake. Two smaller tunnels excavated on both sides of the bypass tunnel and backfilled with concrete prevent water from eroding the ground if the lining is offset in an earthquake. Inside the bypass tunnel, a heavily armored carrier pipe rests on sliding cradles that can shift within the vault as an earthquake offsets the tunnel, ensuring uninterrupted water flow.

The Claremont Tunnel has garnered two prestigious awards: the 2006 ASCE San Francisco Section’s Award of Special Innovation, and the 2009 ASCE OPEL/OCEA Charles Pankow Innovation Award for its novel design features.