The plan to build a second subway line serving Manhattan’s congested East Side has been on the city’s drawing board for eight decades. Now, having withstood financial crises and opposition by residents near the construction zone, the $4.45-billion first phase of the Second Avenue subway project is under way, with 7,200 ft of tunneling almost completed out of a total of 15,000 ft planned. And as crews begin freezing a 150-ft stretch of earth for the second tunnel, they also are trying to thaw the hearts and minds of opposition groups.
With the help of Rockaway, N.J.-based subcontractor Moretrench, a joint venture of Skanska, Schiavone and Shea (S3) has begun the approximately 10-week freezing operation on the east tunnel as part of its $393-million contract. By the time the 22-ft-dia tunnel-boring machine finishes its north-south excavation of the west tunnel and comes back out to the launch portal, the stretch will be ready for it, says Gary Almeraris, Skanska project executive. “As we mine through it, we will install an outer 7-in.-thick concrete liner in order to hold up the ground as it thaws and keep water out.” Once mining of that section is completed, the final concrete liner will be installed for both tunnels.
The section should take about a month to mine through, says Michael Horodniceanu, MTACC president. After that, another three months are needed to thaw out the earth gradually to avoid settlement.
The geology includes hills and valleys, schist, sand and silts, and even fault lines, says Tom Peyton, vice president of geotechnical for Parsons Brinckerhoff, which is leading the construction management team. Still, the need to freeze was unexpected. “When you work underground in variable geology, nothing is for sure until you see it,” says Almeraris. “There are only so many holes you can put in the street.”
As a result, tunneling began on the west tunnel first, rather than on the east. The S3 team had gained plenty of experience with ground freezing and TBMs thanks to its recent work on the No. 7 line extension. The team will install 109 double-walled pipes at angles of about 75 ft deep, through which will be fed chilled calcium chloride brine.
The cut-and-cover excavation of the launch box started in 2009 with a combination of controlled blasting and mechanical approaches. “We put a 30-in. gas pipe inside a 42-in. steel carrier pipe to protect it from blasts,” says Peyton.
The S3 team has been digging the west tunnel at an average of 42 ft a day. Up to sixty trucks a day carry out the muck from the huge entrance shaft at 92nd Street. Once the 850-ft-long TBM reaches its 65th Street terminus, it will be disassembled and pulled back to the launch-box portal at 92nd Street to bore the east tunnel, which will provide a link to an existing 63rd Street subway station.
S3 is building access shafts to enable mining of a 970-ft-long, 70-ft-wide and 50-ft-high station cavern at 72nd Street. A joint venture of Shea, Schiavone and Kiewit won the $447-million contract in October.
A joint venture of EE Cruz and Tully Construction has a $350-million contract for a 70-ft-wide, 50-ft-high, 1,000-ft-long cut-and-cover excavation of the 96th Street station structure. As J. D’Annunzio & Sons finishes up a $40.6-million open-cut excavation and utility relocation contract, Judlau Contracting is gearing up after it recently won a $176-million job for the station structure at 86th Street.
Design of the first phase is about complete, says Geoffrey Fosbrook, senior vice president with AECOM, the final designer in a joint venture with Arup. Back in the 1970s when initial designs started on the entire 8.5-mile alignment, says Fosbrook, “they were looking at cut-and-cover construction, soldier piles, timber lagging” for major portions of the tunneling work. He adds wryly, “I don’t think that would pass muster today.” Designers worked extensively with community feedback, in many cases relocating subway entrances in existing buildings, not down through sidewalks. “MTACC has worked hard to iron out the deals necessary to make that happen,” he adds.
Still, lawsuits have been filed by residents concerned about the impact of facilities and entrances, although MTACC officials say those structures should not affect construction. Goodwill efforts and community outreach continue. “Most projects don’t last so long, or [they] are linear,” says MTACC President Michael Horodniceanu. “We are here building in front of people’s living rooms for years.”
He put together a task force of project officials to deal with residents’ concerns. Between 92nd and 93rd streets, workers are alignin construction fencing, making room for sidewalks, improving signage and advertising for local shops. After community feedback, the team hopes the efforts will spread. The effort appears to be working. Last Christmas, Horodniceanu cooked dinner for the crews in the kitchen of a restaurant whose proprietor had been a vocal critic of the project.