Claremont Tunnel Seismic Upgrade
Over the course of two years, Atkinson constructed a concrete-lined horseshoe bypass tunnel, measuring 2,000 linear feet and 16 feet in diameter, to bolster the existing tunnel where it intersects the Hayward Fault. The new tunnel incorporates an expanded vault section, which spans 100 feet across the primary fault zone and encloses an 85-foot-long, six-foot-diameter, three-inch-thick steel pipe designed to protect the water supply from debris in the event of seismic activity.
The vault is designed to compensate for up to 1 foot of creep over the tunnel’s design life and the potential for a 7.5 magnitude earthquake induced offset. This section of tunnel across the fault was designed to accommodate up to 8.5 feet of lateral offset without water-flow interruption. The expanded vault section was designed to protect and maintain a reliable supply of water to East Bay Municipal Utility customers.
The bypass tunnel was excavated using a combination of drill and blast and roadheader methods. In addition to the new bypass tunnel construction, crews systematically performed a tunnel rehabilitation and contact-grouting program of the entire existing 18,065-foot long tunnel to fill considerable voids behind the old concrete lining and repair the lining that had deteriorated over the past 80 years. Other features included the construction of vertical wing walls and sounds walls at the portal to reduce noise levels for residents within 300 feet of the portal entrance.
Seismic upgrade of the Claremont Tunnel received the 2009 Charles Pankow Award for Innovation from the American Society of Civil Engineers (ASCE). Out of 75 projects submitted, the EBMUD Claremont Tunnel Project was recognized for its first-of-its-kind design to secure the water supply to millions of customers in the event of a major earthquake.