New York's Metropolitan Transportation Authority completed tunneling for the first phase of the Second Avenue Subway when a tunnel boring machine (TBM) reached the Lexington Avenue-63rd Street station, breaking into the existing tunnel.
The completion of tunneling marks a major milestone in the $4.45 billion project that will provide service from 96th Street to 63rd Street as an extension of the Q train.
The TBM began its journey in March and completed the east (northbound) tunnel after making a tight, westerly curve into the existing 63rd Street Station. The tunnel will now receive the concrete lining, which provides the permanent tunnel structure. The work is part of the initial $392 million tunnels and shafts contract that was awarded in March 2007 to Skanska, Schiavone and Shea Tunnel Constructors, JV.
The 485-ton, 450-foot-long TBM used a 22-foot diameter cutterhead to mine 7,789 linear feet averaging approximately 60 linear feet a day. The average depth of the tunnel is 70 feet. During the first 200 feet, the TBM mined through ground which has been frozen, a technique which engineers employ to harden soil, or decomposed rock, enabling the excavation process.
The TBM began mining the 7,209 linear-foot west (southbound) tunnel in May 2010 from the launch box at 92nd Street and was then disassembled and pulled back to 92nd Street where it started its second run this spring to mine the east tunnel.
Work is currently underway to rehabilitate the Lexington Avenue-63rd Street station to accommodate the future Q extension. It will now take approximately three weeks to partially disassemble and pull back the TBM through the tunnel by locomotive. The TBM will be completely dismantled once it returns to the launch box and will be sent back to the contractor’s facilities.
Phase I of the Second Avenue Subway will serve more than 200,000 people per day, reducing overcrowding on the Lexington Avenue Line and restoring a transit link to a neighborhood that lost the Second Avenue Elevated in the 1940’s.
When Phase I is complete in December 2016, it will decrease crowding on the adjacent Lexington Avenue Line by as much as 13 percent, or 23,500 fewer riders on an average weekday. It will also reduce travel times by up to 10 minutes or more (up to 27 percent) for those on the far east side or those traveling from the east side to west midtown.
The line is being built in phases, with the Phase I of the Second Avenue Subway providing service from 96th Street to 63rd Street as an extension of the Q train, including three new ADA-accessible stations along Second Avenue at 96th, 86th and 72nd Streets, and new entrances to the existing Lexington Avenue-63rd Street Station at 63rd Street and Third Avenue.
