Claremont Tunnel Seismic Upgrade

The Claremont Tunnel Seismic Upgrade project protects the tunnel and nearby water supply in the event of seismic activity. The tunnel carries treated water from the Orinda Filtration Plant through the Berkeley Hills to three distribution aqueducts and accounts for 70% of the water supply for EBMUD's customers. Atkinson constructed a concrete-lined horseshoe bypass tunnel measuring 2,000 linear feet and 16 feet in diameter. This work enhances the existing tunnel's structural integrity, particularly where it intersects the Hayward Fault. The new tunnel design incorporated an expanded vault section spanning 100 feet across the primary fault zone. In this vault, an 85-foot-long, six-foot-diameter steel pipe, three inches thick, was installed to safeguard the water supply against debris in the event of an earthquake.

The vault's engineering considered the need to accommodate up to 1 foot of creep over the tunnel's design life and the possibility of a 7.5 magnitude earthquake-induced offset. This section of the tunnel, spanning the fault, was specifically designed to withstand up to 8.5 feet of lateral offset without disrupting water flow. The expanded vault section played a crucial role in safeguarding and ensuring a consistent water supply for East Bay Municipal Utility customers.

To create the bypass tunnel, a combination of drilling and blasting techniques, as well as roadheader methods, were employed for excavation. In addition to the construction of the new bypass tunnel, a comprehensive tunnel rehabilitation and contact-grouting program were systematically executed throughout the entire existing 18,065-foot tunnel. This program aimed to fill significant voids behind the aged concrete lining and address the deterioration that had occurred over the past 80 years. Additionally, vertical wing walls and sound walls were constructed at the portal to mitigate noise levels for residents residing within 300 feet of the portal entrance.

The upgrade of the Claremont Tunnel earned the 2009 Charles Pankow Award for Innovation from the American Society of Civil Engineers (ASCE). Out of a pool of 75 projects submitted, the EBMUD Claremont Tunnel Project was recognized for its pioneering design, which was crucial in securing the water supply for millions of customers in the event of a major earthquake.