The first phase of the Second Avenue Subway extension in the Upper East Side of New York has opened to the public, following a near 100 year wait.
The project was first proposed in 1929 but was subsequently delayed several times over the last century. The Metropolitan Transportation Authority (MTA), which is responsible for public transportation in New York, said that it was New York City’s biggest expansion of the subway system in 50 years.
The first phase of twin tunnels has cost $4.45bn (£3.6bn) and runs from East 63rd Street to East 96th Street, connecting into the existing metro system. However, when complete, the full-length subway line will run 13.7km along Manhattan’s East Side from 125th Street in Harlem to Hanover Square in Lower Manhattan with 16 new stations.
Three separate Skanska joint venture (JV) teams – S3 Tunnel Connectors (Skanska, Schiavone, Shea), STJV (Skanska, Traylor Brothers) and CSJV (Comstock, Skanska) – worked simultaneously to complete different sections of the project.
“The scope of the project was immense: boring two new subway tunnels 33 city blocks long that included accommodation for three new stations and the miles of connections – water, sewer, electrical, utility and even traffic signal wiring – that ran along and through it,” said Skanska USA civil vice president of operations Gary Almeraris.
Almeraris added that to create an “enormous” subterranean “launch box” or starting point where the tunnel boring machine (TBM) could be assembled and start its work, 408,000t of rock was excavated in the construction of the new 86th Street station alone.
“We engineered a special underground support system for a 30-storey residential tower in order to safely excavate the foundation of the building to create a space for an escalator at the corner of 83rd Street, for an entrance to the subway station,” explained Skanska executive vice president Mike Viggiano.
Skanska said that the construction techniques used differed between the two tunnels. It said that while the west tunnel had gone through predictably hard Manhattan schist (rock), the East tunnel path traversed a “sloppy, messy material” filled with water and soil, making it almost impossible to dig a clean path.
“We did something really cool – we froze the ground,” said Viggiano. “Our team drilled pipes into the ground and filled it with chilled brine to harden the soil and made it act like rock. That process took about four months and gave us a safe, solid structure for the project.”
It is estimated that the first phase will serve an estimated 200,000 people a day.
The initial phase is an extension of the existing “Q” line, but will be rebranded the “T train” when the full project is complete.