VTA has just made a $76 million purchase to help bring BART to Santa Clara. The transit agency purchased its Tunnel Boring Machine (TBM), a massive piece of machinery that will drill a tunnel for the BART tracks to travel through to connect San Jose and Santa Clara.
VTA has already started preparing for the TBM’s arrival at its work site. In early August, work began at VTA’s Newhall Yard, near the Santa Clara Costco, to help make room for the boring machine. It’s the key piece in the expansion that will create five miles of train tracks in both directions.
What is a Tunnel Boring Machine?
VTA says the TBM will “remove soil deep from underground forming a tunnel, while keeping the street above intact, like a mole.”
There is a large cutterhead at the front of the TBM, which rotates and digs through soil and rock. A conveyor system inside the machine helps move the soil and rock out of the hole.
VTA released a diagram of the TBM, which shows the different parts, including the cutterhead, bulkhead, compressed air lock, screw conveyor, excavation chamber, drive motors, thrust rams, segment erector and tail seals.
How big is the TBM?
According to VTA, the TBM is nearly 54 feet in diameter. The agency says it will be designed specifically for this project to meet the “project’s unique characteristics and requirements.”
This project is unique because it’s one of the first single-bore tunnel systems used in America. All of the tracks, trains, boarding platforms and other parts of the facility will exist in a single tunnel.
What’s more, the TBM itself is the third largest ever built according to VTA. The largest one used was in Hong Kong. The second largest was “Big Bertha,” which was used in Seattle.
How will VTA ensure the BART tunnel is safe?
To ensure the tunnel stays intact, crews will use cement tunnel lining segments installed as the TBM moves forward in creating the underground tube.
Special measures will be taken to ensure that the pressure from the soil and water do not compromise the stability of the tunnel, especially if there is an earthquake.
In the end, the interior diameter of the tunnel is expected to be 48 feet, with approximately 4 feet of concrete and other material surrounding it.
Where will the Tunnel Boring Machine travel to connect Santa Clara and San Jose?
It will still be a few years before the TBM arrives in San Jose. There are 18 months of construction that still need to be done at the plant in Germany that is making the machine. Then, it will be shipped to the Newhall Yard, where it will take about six months to set up.
Once the machine is ready, VTA will start the digging east toward the Berryessa/North San Jose BART Station. It is expected to dig anywhere from 30 to 40 feet each day. At that pace, the five-mile-long tunnel should take about three to four years to complete.
The TBM is expected to emerge at the East Portal on the east side of Highway 101 near Las Plumas Avenue in San Jose.
For more details on the Tunnel Boring Machine and the VTA’s plans for the BART extension into Santa Clara, visit the VTA’s website and search for “Bart Silicon Valley Phase II Project.”
