The Central Subway’s two tunnels — one for northbound trains and one for southbound trains — will be constructed using state-of-the-art excavators known as tunnel boring machines (TBMs). For the past few months, TBM supplier Robbins has been busy building the Central Subway’s two TBMs — and we have photos of their progress.
The Central Subway tunnels will travel beneath downtown San Francisco, bypassing congested streets to quickly transport customers through some of the city’s most bustling and heavily traveled areas. Starting next year, two TBMs will build the tunnels, digging at a rate of about 40 feet per day far beneath the surface of the city. Prefabricated tunnel segments will be put in place as the TBMs advance, with a crew of about seven workers operating the machines and welding the segments together.
Each TBM consists of a rotating cutting wheel (the cutter head), a cylindrical steel shell (the shield) and a 300-foot train of tunnel-building contraptions (the tail). It takes about a year to construct this complex construction equipment.
Once the TBMs are ready, they’ll by shipped across the Pacific Ocean, arriving in San Francisco next year to begin building the city’s first subway tunnel in decades.
Here are photos of the Central Subway’s partially built TBMs:
Part of the TBM cutter head support.
A cylindrical segment that will be part of the TBM shield.
Another view of the cutter head support.
Parts to be incorporated into the TBM tail.
More TBM tail components.