WSP led conceptual, preliminary and final design for the subway extension, assisted the MTA in development an overall construction program and contract packaging arrangements, provided construction support services, and—as a consultant to the contractor—served as systems integrator, responsible for ensuring that mechanical-electrical-plumbing (MEP) systems perform as designed.
The 34th Street station, the first new station in 25 years and the 469th in the system, is deep by New York City subway standards—125 feet underground—and is reached by escalators and inclined elevators. Most New York City subway stations are relatively shallow and easily reached by stairways, in accordance with William Barclay Parsons’s plan for the subway system he designed in the 1890s.
The extension of the No. 7 subway line runs from the previous terminus at Times Square, west under West 41st Street, and south under 11th Avenue to West 34th Street, although tail tunnels for train storage extend to West 25th Street. As part of the design process, more than a half-dozen other alignments were studied before the route under 11th Avenue was selected.
Designing the project posed a number of challenges, including:
excavation and construction of a tunnel under the Port Authority Bus Terminal that also served as a receiving chamber for the TBMs;
tunneling and construction in close proximity to existing structures, including two Amtrak tunnels and three tubes of the Lincoln Tunnel under which the new tunnel passes. In some cases the new tunnel comes as close as 20 feet to existing tunnels;
extensive underpinning of subway station at 8th Avenue and 41st Street and underpinning existing No. 7 tail track tunnel columns; and
coordinating the design of No. 7 systems building structures with the designs of private development overbuild structures.
The need to avoid the existing tunnels, buildings and other infrastructure required relatively deep tunnels—about 100 feet deep in most places. The tunnels were excavated by two tunnel boring machines (TBMs). As the TBMs dug the tunnels, a cavern for the station was mined through the drill-and-blast method.
Excavation for the tunnels began in May 2009 and was completed by June 2010. The TBMs were lowered into a shaft at the southern end of the tail tunnel and removed from a shaft near the Port Authority Bus Terminal in August 2010, once excavation was complete.
