Client Santa Clara Valley Transportation Authority (VTA) just reached a major milestone with the purchase of the near 16.4m diameter TBM that will bore the 8km of single bore tunnel for the US$6.9bn BART Silicon Valley Phase II Project (BSVII) in San Francisco.
This $76M TBM will be one of the largest machines ever built. Multiple payments will be made to the manufacturer, Herrenknecht at key milestones of design, production, delivery, assembly, and launch of the TBM.
The significant tunnel diameter 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, whilst the 14.6m i.d. thickness of the segmental lining is based on the pressure from the soil and water surrounding the tunnel and important safety requirements in the event of an earthquake.
Herrenknect will design, manufacture, assemble, test, and then disassemble the TBM at their factory in Schwanau, Germany. Approximately 18 months after manufacturing begins, the TBM will be shipped from Kehl, Germany across the ocean to California to be reassembled on-site at the West Portal, located at the future Newhall Yard. Reassembling the TBM will take approximately six months on-site before it is ready to be launched into the area’s high water tables and geology of sands, gravel, silts, and clays in the South Bay.
The TBM will launch at the West Portal and will dig 9m – 12m each day travelling east towards the Berryessa/North San Jose BART Station, taking approximately three to four years to complete the tunnel. Once tunnelling is complete, the TBM will emerge above ground at the East Portal on the east side of US 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 tunnelling 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.
During the May 2022 VTA Board of Directors meeting, the Board awarded Kiewit Shea Traylor, a joint venture between Kiewit Infrastructure West Co, JF Shea Construction, Inc., and Traylor Brothers Construction (KSTJV), the tunnel and trackwork contract for VTA’s BART Silicon Valley Phase II Extension Project at price of US$235M.