New Crystal Springs Bypass Tunnel Excavation Completed
On March 24, the Tunnel Boring Machine (TBM) for the New Crystal Springs Bypass Tunnel reached its goal: termination of excavation at the base of the completed North Shaft, after traveling 4,200 feet from the South Shaft, where it was launched on November 10, 2009. The best day of excavation was 83 feet, and the overall average since start of excavation on November 10 was 40 feet per day. The TBM was designed by M.L. Shank Co., the shield was manufactured by Hitachi Zosen, and the cutters were provided by Herrenknecht, but most other components were fabricated and assembled on-site between July and October of 2009. Shank/Balfour Beatty JV is the general contractor for the project, and Jacobs Associates is providing construction management services for the project owner, the San Francisco Public Utilities Commission.
The planned construction approach was to complete the North Shaft, including the steel pipe installation by mid-2009, and to leave the shield in place when TBM excavation was completed. The TBM will be "gutted" and salvageable parts backed out of the tunnel and retrieved from the South Shaft. The next big piece of work includes installation of welded steel pipe in the tunnel and backfill with cellular grout, as well as installation of near-surface pipelines, valves, and vaults at the South Shaft. Shutdown #1, which involved near-surface piping at the North Shaft being tied into the Sunset Supply Pipeline during a limited system-wide outage, was completed ahead of schedule on March 2.
