To launch, the machine pushed off of a steel frame as its cutter head began to spin. As it tunnels, the machine will stop every five feet to install the concrete segments that make up the tunnel’s lining. The concrete segments are installed within the back of the TBM’s cylindrical shield. The machine lifts the segments into place, and then crews bolt them together. Hydraulic jacks within the shield then push off of the newly installed tunnel lining, propelling the massive machine forward. A crew of about 10 people operates the machine and bolts the tunnel segments together.
The Central Subway is expected to open to the public in 2019.