Claremont Tunnel Seismic Upgrade
The Claremont Tunnel crosses the active Hayward Fault to deliver water to over 800,000 residents in Northern California. Originally built in 1929, the tunnel required significant seismic upgrades. The project earned the Charles Pankow Award for Innovation from the American Society of Civil Engineers. It 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.
Atkinson began work on the Claremont Tunnel in 2004. Over the course of two years, crews 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 one foot of creep over the tunnel's design life and can endure a 7.5-foot, earthquake-induced offset. Side drifts on both sides of the tunnel were filled with lean concrete to prevent erosion to the host rock should an offset occur.
In addition to their work on the bypass, crews also rehabilitated the existing 18,065 linear-foot tunnel, performing systematic contact grouting throughout.