New Milestone for No. 7 Subway Extension Project

7 Line Subway Extension Photo

The second of two 1,000 ton tunnel boring machines has reached the chamber adjacent to the current terminus for the No. 7 train underneath 42nd Street. This marks a major milestone in the $2.1 billion project that will extend the No. 7 line to 34th Street and will support the growth of an emerging community on the West Side. The project is funded by the City of New York and managed by the MTA.

The tunnel boring machine (TBM) broke through into 200 ft. x 50 ft. x 40 ft. deep receiving chamber just below the Port Authority Bus Terminal in close proximity to the bus terminal foundation and utilities, as well as the 8th Avenue Subway Line. This is where the new tunnels will connect with the existing No. 7 Line terminus at Times Square.

"This marks the final leg of the second of two, 1,000-ton tunnel boring machines that have mined more than a combined 9,300 feet to reach this point," MTA Chairman and CEO Jay H. Walder said. "It's a major milestone working toward the completion of a project that will increase capacity within our transit system and help redevelop a vital part of our city that will spur future growth."

The two TBMs will be partially disassembled here and backed up to where they started tunneling at 26th Street and 11th Avenue where they will be lifted out of the shaft.

The receiving chamber under the bus terminal was excavated by controlled drill and blast in 2009. Through coordination and cooperation with the Port Authority, the 24-hour construction operation was completed in six months instead of 2-3 years as originally planned. The work was coordinated in a way that minimized disruption to the bus terminal and the traveling public, and was completed without a single complaint from the public.

The TBMs were launched in the summer of 2009 from an underground assembly chamber located at 26th Street. As the machines mined, they placed pre-cast concrete lining rings along the excavated tunnel, making up the permanent liner of the finished tunnel.

Tunneling north from 34th Street presented unique challenges, as the tunnels run under Amtrak/NJ TRANSIT tunnels, tunnels to the former New York Central Line, the Lincoln Tunnel and the Port Authority Bus Terminal and ramps.

Work will now commence on station entrances and finishes, as well as support facilities such as ventilation and traction power substations. Customers will be able to take advantage of the new service in December 2013 as scheduled.