The Santa Clara Valley Transportation Authority (VTA) has purchased a the Tunnel Boring Machine (TBM) that will dig the tunnel for the Bay Area Rapid Transit (BART) Silicon Valley Phase II Project (BSVII). The tunnel will contain five miles of train tracks in both directions and three station platforms to provide safe and efficient travel separated from congested roadways. The $76 million TBM will be one of the largest machines ever to be built.
The TBM will remove soil deep from underground forming the tunnel while keeping the street above intact. The front of the TBM includes a cutter-head, which rotates to dig through soil and rock. The material will then be removed through a conveyor system within the machine.
Size of the TBM
The TBM will be nearly 54 feet in diameter and is being specifically designed and built to meet this BSVII’s unique characteristics and requirements. The size of the tunnel was determined by the space needed for the tracks, trains, boarding platforms and other equipment and facilities needed in the tunnel to operate safely and efficiently. Massive cement tunnel lining segments will be installed, as soil is removed to create the structurally sound tube underground.
The thickness of the tunnel lining is based on the pressure from the soil and water surrounding the tunnel and important safety requirements in the event of an earthquake. The inner diameter of the tunnel will be 48 feet and the exterior of the tunnel will be just under 52 feet.
Santa Clara VTA’s TBM for the project will be the third largest TBM ever built. The largest TBM, Tuen Mun-Chek Lap Kok in Hong Kong, was 57 feet and 10 inches and Big Bertha in Seattle, Wash., was 57 feet and three inches.
Manufacturing of the TBM
The TBM will be purchased from Herrenknecht, a German manufacturing company that specializes in building customized tunneling equipment such as TBMs for projects worldwide. Herrenknect will design, manufacture, assemble, test and then disassemble the TBM at their factory in Schwanau, Germany. The TBM will be uniquely designed to operate in areas with higher water tables and the geology of sands, gravel, silts, and clays in the South Bay.
Approximately 18 months after manufacturing begins, the TBM will be shipped from Kehl, Germany, to California to be reassembled on-site at the West Portal, located at the future Newhall Yard. Reassembling the TBM will take approximately 6 months on-site before it is ready to be launched.
The TBM will launch at the West Portal and will dig 30 to 40 feet each day, traveling east towards the Berryessa/North San Jose BART Station, taking approximately three to four years to complete the five-mile-long tunnel. Once tunneling is complete, the TBM will emerge above ground at the East Portal on the east side of U.S. 101 near Las Plumas Avenue. Once it reaches the surface, it will be disassembled and the remaining parts and material are planned to be reused to the extent possible.
In preparation for the TBM arriving, VTA will be preparing the West Portal for tunneling operations by constructing on-site access points, excavating the portal, constructing and operating the facilities needed to produce the tunnel lining and establishing the excavated materials bin.
