Crews from the Southland Tutor Perini JV met underground recently at the completion of one of four tunnel headings that comprise the New Irvington Tunnel project, a 3.5-mi component of San Francisco Public Utilities Commission’s $4.6 billion Water System Improvement Program (WSIP) to repair, replace, and seismically upgrade the Hetch Hetchy Water System’s aging pipelines, reservoirs and dams.
WSIP includes more than 80 projects spanning seven counties from the Called a “hole-through” in tunneling terminology, the road header teams from the Irvington Portal in Fremont and the Vargas Shaft 4,500 ft away shook hands somewhere under the mountainside and formally completed this section of tunnel excavation.
According to SFPUC General Manager Ed Harrington, the new tunnel will provide an additional seismically-designed connection between water supplies from the Sierra Nevada Mountains and the Alameda Watershed to Bay Area water distribution systems.
Dan McMaster, Hatch Mott MacDonald, the New Irvington Tunnel’s construction manager, says, “We are almost 50% complete on tunnel excavation and now the crews will be heading east out of Vargas to meet up with Alameda West Portal heading next year.”
McMaster says the tunnel was excavated using conventional mining methods, including a road header (a tracked tunneling machine) and, in sections of hard rock, controlled detonations. In May 2011, a 55-ton road header was lowered down the 115-ft Vargas Shaft and began to grind its way west. A month later, miners at the Irvington Portal in Fremont began tunneling east and set the two crews on a collision course, according to the SFPUC.
Following the hole-through, miners are now preparing the tunnel for the installation of 102-in. diameter steel pipe. The pipe, manufactured in California, is installed in 50-ft sections and welded together inside of the tunnel. The much longer 14,400-ft Alameda West-Vargas tunnel segment is currently being excavated and is expected to hole through in fall 2013. Construction of the entire project is scheduled for completion in fall 2014.
In other WSIP news, the SFPUC awarded a $31.3 million construction contract to Steve P. Rados, Inc. to begin work on the seismic retrofit of two major water pipelines at the three traces of the Hayward Fault near the Mission Blvd/I-680 Interchange in Fremont. The professional service firm of EPC Consultants was also awarded an $8.5 million contract to assist the SFPUC in the construction management of the project.
The project will include the construction of a new 300-ft-long articulated concrete vault at one fault trace and a new 2,000-ft segment of BDPL 3 pipeline across the fault traces. The project also addresses improvements to BDPL 4.
SFPUC and URS consulting engineers designed a system that includes 72-in.diameter ball joints plus slip joint, and articulated concrete vault to accommodate the planned displacement. The new articulated concrete vault has been extensively tested at Cornell University, says the SFPUC. The ball joints have been designed to withstand the displacement of an earthquake on the Hayward Fault.
Construction is anticipated to begin in August 2012 and is the last of the large projects to be awarded for the WSIP infrastructure upgrades. They include more than 80 projects spanning seven counties from the Central Valley to Downtown San Francisco of which 74 projects are either in construction or completed.