A $12.2 billion extension of California’s Bay Area Rapid Transit heavy-rail system has reached a major milestone: Time to send in the tunnel boring machine.
The Santa Clara Valley Transportation Authority reports it has completed excavation for the West Portal Launch Structure, from which the TBM will begin its work 75 feet underground between Santa Clara and San José.
In 2023, VTA paid $76 million for a 54-foot-diameter Herrenknecht tunnel boring machine customized for the Phase II extension to operate in higher water tables and the geology of sands, gravel, silts and clays found in the region. The TBM will travel 30-40 feet per day east from the West Portal Launch Structure and complete the final five-mile tunnel in three to four years.
The electric-powered TBM is being assembled on site. The 48-foot-diameter tunnel will contain two independent track ways, one for each direction of train travel.
The TBM's cutter-head rotates to dig, while excavated soil, rocks and debris are removed through a conveyor system and hauled off site. The same conveyor system sends in the concrete lining segments, each weighing 40,000 pounds. An estimated 54 lining segments will be installed each day and sealed with grout.
Powered byThe project’s tunneling and track work contract was awarded to the Kiewit Shea Traylor joint venture, and crews first broke ground on the launch structure in 2024.
When finished, the BART Silicon Valley Phase II Extension Project will extend the BART Silicon Valley service across four new stops from the Berryessa Station through downtown San José to Santa Clara via five miles of subway tunnels and 48 heavy rail vehicles. The resulting single-bore infrastructure will be owned and operated by VTA.
The BART Silicon Valley Phase II Extension Project is set to become the largest infrastructure project in Santa Clara County after work is completed in 2034. The project’s $490 million construction management contract was awarded to Bechtel Corporation, while the $125 million general engineering contract went to Mott McDonald/PGH Wong Engineering Joint Venture.
According to VTA, the Phase II extension will serve 55,000 riders daily. Phase I of the BART Silicon Valley Extension Project opened in 2020 as a 10-mile, two-stop extension of the BART system from Warm Springs Station in Fremont, proceeds through Milpitas and ends in the Berryessa area of north San José.
