A video posted on YouTube captures the moment when a roadheader, an enormous tracked tunneling machine, breaks through a wall of rock and earth and workers step through to greet their fellow miners on the other side. Titled "NIT's Road Header Rendezvous," the clip shows one grinning crew member shouting congratulations over the drilling noise as he reaches out to shake hands with a teammate.
The clip shows the moment on June 12 when the two mining crews working on the 3.5-mile New Irvington Tunnel project—the NIT—met below ground to complete the first of four tunnel headings. Two teams of miners had been steadily excavating an 8.5-ft-dia corridor, with one group moving eastward from the tunnel's Irvington Portal in Fremont and the other heading westward from the Vargas Shaft 4,500 ft away.
The $318-million New Irvington Tunnel, begun in May 2011, is one of 80 projects that comprise the San Francisco Public Utilities Commission's (SFPUC) Water System Improvement Program (WSIP). The $4.6-billion program will renovate and seismically upgrade the Hetch Hetchy Water System.
That network of waterworks channels Sierra Nevada runoff in the Hetch Hetchy Valley in Yosemite National Park 160 miles to the San Francisco Bay Area, providing water to about 2.6 million people in San Francisco, Alameda, Santa Clara and San Mateo counties. The program began in 2003 and is expected to be completed in 2016.
When finished, the New Irvington Tunnel project will parallel the existing water tunnel from the Sunol Valley south of Interstate 680 to Fremont.
With the Irvington-Vargas Shaft hole-through achieved, workers now will turn the roadheader eastward and plow toward another rendezvous, with a crew heading west from the line's Alameda section—a tunneling distance of 14,400 ft.
To keep the workers safe and the tunnel work flowing, overhead water fissures are blocked and a network of 23 dewatering wells has been installed. After the digging is done, crews will install a 103-in.-dia steel pipe composed of 50-ft-long segments. It can convey up to 300 million gallons of water per day to the Bay Area.
Southland Tutor Perini, a joint venture of Sylmar-based Tudor Perini Corp. and Southland Contracting Inc., Fort Worth, Texas, is the project's contractor team. Hatch Mott MacDonald, headquartered in Milburn, N.J., is the construction manager.
SFPUC project manager David Tsztoo says that building an alternative pipeline across the region's Sheridan Valley gives the agency the freedom to take the existing 80-year-old tunnel out of service for much-needed maintenance and repair.