OAKLAND, CALIF.—The East Bay Municipal Utility District Claremont Tunnel Seismic Upgrade Project was awarded the 2009 Charles Pankow Award for Innovation from the American Society of Civil Engineers. The project was designed to safeguard the water supply of more than 800,000 people in the Oakland area from a magnitude 7 earthquake. The Claremont Tunnel, built in 1929, crosses the active Hayward Fault as it carries water more than three miles from the Orinda Water Treatment Plant to aqueducts serving all or parts of Oakland, Berkeley, Alameda and eight other communities. The winning project involved construction of a 1,570-foot-long bypass tunnel that runs through the fault and connects to the Claremont Tunnel east and west of the fault zone.
AMEC Geomatrix characterized the geologic conditions along the bypass tunnel alignment and provided the design team with the geotechnical and earthquake parameters needed to design the bypass tunnel. Jacobs Associates was responsible for the overall design and construction management support.
According to Jacobs, the Claremont Tunnel design was the first of its kind. An expanded vault section across the Hayward fault was designed to accommodate as much as 8.5 feet of lateral offset without interruption of water flow. The reinforcing around the vault was designed to curve like a spine in an earthquake, while two side drifts—smaller tunnels on both sides of the bypass tunnel—were completely backfilled with concrete to prevent water from eroding surrounding ground if the lining cracked after an earthquake.
Inside the bypass tunnel, a 130 million-gallon-per-day, 6-foot-diameter, 3-inch-thick steel carrier pipe provides additional protection for water conveyance. This is enough to maintain lifeline service to customers following a magnitude 7.0 earthquake. The pipe rests on sliding cradles that enable it to shift within the vault as an earthquake moves the tunnel.