New Crystal Springs Bypass Tunnel
Summary
The New Crystal Springs Bypass Tunnel was part of the SFPUC’s $4.6 billion capital improvement program to repair and seismically upgrade its aging pipelines, tunnels, reservoirs, and dams. The SFPUC determined that replacement of the pipeline with a deep underground tunnel and pipeline would most effectively ensure continued delivery of drinking water after a major seismic event.
- 4,200-foot long (1,280 m), 12-foot-diameter (3.7 m) conveyance tunnel
- 8-foot (2.4 m) welded steel pipe final lining
- Highly variable rock conditions
- Seismic upgrade of critical infrastructure
Scope of Work
Delve Underground led project construction management for the SFPUC, which included 11 subconsultants and 2 SFPUC staff members. Construction management services consisted of resident engineering, office engineering, scheduling, cost control, contract administration, quality assurance inspection, and environmental monitoring.
This new 4,200-foot-long (1,280 m) tunnel lies at depths of up to 160 feet (49 m) underground. It was excavated using a 12-foot-diameter (3.7 m) shielded disc-cutterhead tunnel boring machine, which encountered highly variable rock conditions, typical of Franciscan Complex bedrock. Initial tunnel support consists of precast concrete segments, which house the 8-foot-diameter (2.4 m) welded steel pipe final lining.
Challenges & Innovations
Project challenges included environmental restrictions, proximity to homes, and a request by SFPUC Water Supply and Treatment to shorten the duration of a shutdown to minimize project risk.
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Large Project of the Year Award ASCE San Francisco Section, 2011
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Liberty Mutual Safety Award ASCE San Francisco Section, 2010