Bay Tunnel
The Bay Tunnel is a, utility tunnel from Newark to Menlo Park. It is the first bored tunnel under the San Francisco Bay. As part of the Hetch Hetchy water system, the tunnel carries drinking water for the City and County of San Francisco and is owned and operated by the San Francisco Public Utilities Commission.
Background
After reaching the Bay Area, the Hetch Hetchy aqueduct split into four pipelines which all cross the Hayward fault. Pipelines 1 and 2 cross the San Francisco Bay to the south of the Dumbarton Bridge, partially upon a 1920s-era bridge and partially upon the Bay floor. Pipelines 3 and 4 run around the south of the bay. The four pipelines were built between 1925 and 1973.By 2009, pipelines 1 and 2 across the bay leaked badly, causing plants to grow at the seams. The pipelines were also vulnerable to rupture due to earthquakes. However modern federal environmental laws made accessing and maintaining the pipeline difficult.
Construction
The Bay Tunnel replaces the existing bay crossing of Bay Division Pipelines 1 and 2, and connects to a new Bay Division Pipeline 5. Construction began in, and the tunnel was finished on and began service in. The project finished on-time and under-budget at $218 million, down from the $313 million estimate.Construction required digging two shafts; one to assemble and launch the tunnel boring machine, and one to receive and extract it. The launching shaft was dug next to the existing Ravenswood Valve House in Menlo Park, to a cylindrical diameter of and depth of. During construction the tunnel featured a rail people-mover, overhead earth conveyor belt, and other utilities. Excavation rates reached up to per day. The receiving shaft was built in Newark to a cylindrical diameter of and depth of. Ground freezing was used to prevent groundwater movement and avoid leakages during excavation of the receiving shaft. Fifty freeze pipes were installed to a depth of around the circumference of the shaft, and additional freeze pipes were installed through the center to freeze the bottom of the shaft.
The tunnel's construction is part of SFPUC's $4.6 billion Hetch Hetchy Water System Improvement Project which was a response to the 1989 Loma Prieta earthquake.