A $4.45-billion, nearly decade-long effort to build the first major expansion of New York City’s subway system in 50 years was bound to have surprises along the way, but few were as showstopping as a stretch of fractured rock below the intersection of Second Avenue and 91st Street. The first phase of the Second Avenue Subway, which runs 1.8 miles on Manhattan’s East Side, already promised huge tasks of building three new stations below 72nd, 86th and 96th streets; upgrading a station at 63rd Street and connecting to a tunnel built decades ago in East Harlem; and tackling that work in a crowded mix of massive high-rise and aging low-rise buildings.

The project that extends the Q Line north and now serves 176,000 passengers daily—greatly reducing congestion on the transit system’s only other Upper East Side service on Lexington Avenue—also has set a new bar for station design that optimizes rider experiences and uses modern technology.

But to get there, there was a lot of rock to carve, muck to remove, foundations to support and—in the conditions under that tricky intersection—ground to freeze. Despite multiple boring tests, the project team found a patch of softer soil and unstable rock at the eastern tunnel’s planned mouth late in planning because it was right under the 91st Street-Second Avenue intersection, and it threatened to hold up progress of the tunnel boring machine (TBM) needed to cut caverns for the two new stations further south.

S3 Tunnel Connectors—a consortium of Skanska USA, Schiavone and J.F. Shea Construction on that contract—devised a backup plan to drill the west tunnel first and then use a ground-freezing technique in the east tunnel area that would stabilize the soil enough for the TBM to bore through the area. That work, which took place in 2011, also required shortening the west tunnel’s length in that contract and transferring it to a separate mining phase in order to stay on schedule. The technique, which entailed drilling small pipes into the ground and circulating chilled brine through them to freeze the soil enough to behave like rock, had worked for Skanska on the 7 Line subway extension project on Manhattan’s West Side, and it did the trick on Second Avenue.

“We had to decide what to do on the spot,” says Chu Ho, chief geotechnical engineer on the project at Arup, which in a joint venture with AECOM led all engineering and architectural design services.

Such quick solutions led to what may be the project’s most notable achievement of all—hitting its fiscal and schedule targets, says Craig Covil, Arup principal. After breaking ground in 2007, the Metropolitan Transportation Authority set a goal in 2009 to open the new line in December 2016, and made it with a free preview for dignitaries on New Year’s Eve.

“The clear highlight was opening on time and on budget,” he says. “Revenue service started on the morning of Jan. 1.”

Massive Partnership

MTA as project owner was conductor of an orchestra of contractors and consultants, with big partnerships in star roles. Those involved Arup and AECOM on design and structural, civil, geotechnical and MEP engineering; contractor teams including S3, other Skanska ventures with Traylor Brothers and with L.K. Comstock; an E.E. Cruz- Tully Construction joint venture, among others; and WSP Parsons Brinkerhoff, now WSP, as construction manager.

The design side had 32 subconsultants, says Chris Bennett, AECOM chief engineer in the New York region. “At the peak of design, we had 350 people on the project.” It worked smoothly on the design front, says Richard Potter, the project’s chief MEP engineer at Arup for 15 years. “We were able to integrate teams from various companies,” he says. “No one was trying to push corporate agendas.”  The same ethic bolstered the construction side, according to Brian Hotchkiss, AECOM project architect on later phases. “Getting all the trades working together, seeing it all on the same page, was a big thing.,” he says.

Such coordination was critical on a project conceived in the 1920s but not  started until 50 years later. After completing several sections of tunnel, city officials facing the mid-1970s budget crisis abandoned the project. Today’s incarnation may one day run 8.5 miles down the East Side if the MTA proceeds with all planned phases, a concept mapped out by the design joint venture, says Bennett. “Phase 2 will take it up to 125th Street,” he says.

There were a number of bumpy moments, of course. In 2009, officials ordered the evacuation of a six-story walk-up building at 93rd Street when inspectors found facade cracks. A pair of controlled blasts went awry three years later, one of which sent chunks of rock and debris up into the street and through building windows, although without causing injuries. City firefighters also had to rescue a sandhog stuck in the mud at the dig’s bottom at 96th Street after heavy rain in 2013.

But the project’s safety record across 15 million worker-hours—a U.S. Occupational Safety and Health Administration recordable incident rate of 2.8 and lost-time accident rate of 1.38—was below industry standards, and there were no deaths.

High Expectations Deep Underground

Two highlights stand out across a decade of construction and nearly two decades of design: the complex, muscular efforts to break, drill, cut and drain the elements to carve the new tunnels and the elaborate, exacting work to create stations that are both striking public spaces and intricate puzzles of utilities and systems behind the walls.

The digging involved boring, excavation, blasting, cut-and-cover and other methods to create 2.65 miles of tunnels and station caverns, including the 800-ft-long TBM launch box that would later become the 96th Street station. The TBM cut 12,800 ft of twin-track, 22-ft-1-in.-dia tunnels and stations that are up to 64 ft wide, 1,600-ft long and 100 ft deep.

The team encountered a stew of geologic conditions. “We ran into hard rock—Manhattan schist—glacial deposits, soft soils, underground water,” says Arup’s Ho.

It all was under a teeming cityscape, packed with utility lines and building foundations of every size and condition, says Richard Giffen, Arup’s chief structural engineer on the project. “We had to modify and protect these buildings, and each station required major modifications,” he says. “Thirty-story buildings have columns that drop down into the project.”

The team undertook great efforts to establish tolerances, measure structural movement, shore foundations, create retention systems, stabilize ground, remove muck and manage water conditions and other stresses, Ho says.

The effort also played matchmaker—connecting south to the 63rd Street Station, which needed a near-complete upgrade, and to already built tunnels to the north, which are at higher elevation than the new alignment, Giffen says. “These were complicated sequences of tying into the existing structures and supports … and in some cases demolishing and rebuilding,” he adds.

Each station was its own epic, requiring a modern battery of ventilation, track, signal, lighting, power and communications systems, along with high standards for air temperature management, passenger navigability and visual appeal through design and artistic finishes.

In order to open column-free spaces for passenger flow, the team had to fit a complex array of mechanical, electrical, drainage and other support systems in tight spaces behind station walls, says Jim Collins, station design manager and coordinator at AECOM. “They didn’t want to use extra cubic yards there,” he says. “At the start, we were designing it all in [two dimensions] because [building information modeling] systems were in their infancy.”

A final payoff is in new station design guidelines for MTA evolving from the final production documents, which are meant to be a flexible, lasting legacy of the Second Avenue undertaking, according to Ken Griffin, AECOM’s chief architect who was on the job in its early days. “We helped them build a road map for what should be in a modern station,” he says.

It captured the project’s merging of old and future, says Don Phillips, a deputy project manager at Arup in the early going. “The subway was 100 years old, but we had to make this a 21st-century, even 22nd-century system.”

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