TBM Lowered at the New Crystal Springs Bypass Tunnel
October 8, 2009 - The Tunnel Boring Machine (TBM) that will be used to mine the New Crystal Springs Bypass Tunnel (NCSBT) was lowered into its launch shaft on September 30, 2009. The single shield TBM and trailing gear are 155 feet long. The main body is 12'-2" in diameter with a taper to its tail shield, which is 11'-11" in diameter because of the potential to encounter squeezing ground. Hitachi-Zosen fabricated the cutterhead and shield, Rotek provided the main bearing, and Herrenknecht fabricated the 17-inch disc cutters. M.L. Shank Co., Inc. designed the machine, and the Shank crew assembled it and built the trailing gear on the project site.
The NCBST will provide redundancy to the existing pipeline and will improve the delivery reliability. The existing pipeline is a 96-inch prestressed concrete cylinder pipe that was installed in 1969 below the hillside along Polhemus Road. The pipeline and soils in this area are subject to failure during high precipitation or major seismic events. This pipeline is a critical link in the transmission system, carrying water from the East Bay to peninsula cities and San Francisco.
Jacobs Associates is leading the construction management team, which includes client (San Francisco Public Utilities Commission) staff and the Shank/Balfour Beatty Joint Venture, which is the general contractor on the project.
Video coverage of the event can be found on www.tunneltalk.com.