Overview

New York City’s Number 7 Subway Line, known as the Flushing Line, is the system’s busiest, linking the borough of Queens to Times Square in Midtown Manhattan. This project extends the existing Number 7 Line subway service via a 1.5 mile extension from Times Square to the new 34 Street – Hudson Yards station located at West 34th Street and 11th Avenue, with additional train storage tracks south to West 25th Street.

About the Project

LiRo, in a joint venture, provided program and construction management for the project, which included the underground station extending approximately 1,200 ft along 11th Avenue from West 32nd Street to West 37th Street. The station features high-end finishes such as stainless steel tile wall panels, painted steel ceiling panels, granite floor tile and entails three public floors: the upper mezzanine, the lower mezzanine, and the platform level. It also includes inclined elevators used for ADA access. Highlighted scope of work included:

• Tunnel excavation, primarily with two Herrenknect Hard Rock Double Shield 22.5′ diameter tunnel boring machines.
• A 950′ by 65′ x 66′ station cavern at West 34th Street, constructed by drill and blast methods of underground construction.
• Installation of five shafts, averaging 110 ft deep and 39 ft in diameter. The shafts were installed both by excavation in soft ground and drill and blast in rock. The finished shafts were lined with steel fiber-reinforced shotcrete.
• Multiple fan plants, HVAC facilities, traction power substations, facility power substations, circuit breaker houses, fare collection and communications and signal rooms.
• Construction of steel and concrete structures for stations and other facilities, construction and installation of tracks, drainage, third rail power and other electrical systems, signals, communications, HVAC, and tunnel ventilation systems.
• Full fit-out of the 34th Street Terminal for operation and commissioned with the Number 7 Subway Line Extension, including major building work to create a complete station.
• BIM Services: 3D modeling, clash detection, and walkthrough and 4D sequencing, scheduling, and tracking.

Project Challenges & Solutions

Accomplishing this massive undertaking presented many challenges associated with boring through a combination of solid rock and soft ground beneath heavily used facilities such as the Port Authority Bus Terminal. Two Tunnel Boring Machines (TBMs) manufactured in Germany by Herrenknecht were used to mine the tunnels through solid rock and for the first time in the world a tunnel boring machine drilled through a “ground freeze” area while simultaneously placing precast tunnel liners. This was accomplished under 11th Avenue between West 26th and West 28th Streets. Controlled “drill-and-blast” methods were used to excavate the underground facilities. Total excavation resulted in over 409,000 cubic yards of rock. The A, C, and E subway routes, running north – south under 8th Avenue, also needed to be protected during construction of the Number Line Extension. These lines, above the work area, required extensive underpinning. There were no disruptions in service to those subway lines throughout the entire construction operation.

Outcome

The new 34th Street Station is a modern marvel with 21st Century amenities that links to 18 subway lines. The extension line was an integral part of the City’s redevelopment plan connecting the rest of the city to this new developing neighborhood and offering easy access to the Jacob Javits Convention Center, the High Line, the Hudson River Park, and ferries.