Under the Streets of New York:

Contractors Construct 200-ft.-long
Mezzanine Under 53rd St.

by Jason Feldman

While standing on the corner of Lexington Avenue and 53rd Street looking for the project office of Slattery Skanska/Gottlieb Skanska, little did I know that 20 ft. below me crews were busy excavating a shaft for an escalator. Drivers and other pedestrians on 53rd Street were entirely unaware as well.

That's exactly what the Metropolitan Transportation Authority/New York City Transit and Slattery Skanska/Gottlieb Skanska, a joint venture, the project's Whitestone, N.Y.-based general contractor, wanted.

The Lexington Avenue and 53rd Street station in Manhattan is a major stop on the city's most crowded subway line. Overcrowding on the platform has been a problem that has dogged the MTA/NYCT since a connection to the No. 6 line was added in the mid-60s.

The connection was placed only at the Lexington Avenue side of the platform and there is only one set of escalators, which caused people to crowd into the first few cars of the E or V trains in order to get off near the escalator. The result has been extreme overcrowding on the narrow platform.

Enter the development team of this $53 million project. A solution was found through the design of a 200-ft.-long mezzanine that will connect the Third Avenue and Lexington Avenue ends. This new mezzanine will do away with the need to use the platform to transfer to the 6 train, thus reducing crowds on the platform.

Easier said than done.

Besides dealing with the usual mess of utilities below the streets of New York, workers also had to close some sections of the platform.

Yet under no circumstances could 53rd Street be closed during the day. The station itself is located under the bedrock of Manhattan. Its famous schist, which provides an excellent support for skyscrapers, is downright lousy if you need to dig through it. The station is almost 70 ft. below street level, which ensured a lot of digging. In addition, the 53rd Street station is located under the water table, with leakage a constant problem.

Decking System Ensures Smooth Traffic Flow
To ensure smooth traffic flow as per New York City Department of Transportation instructions, the development team created a decking system that, instead of just covering the street, goes from building line to building line.

It's one of the first decking systems to include both the street and sidewalk. It's an effective system, which needs to be seen from underground to be fully appreciated. It allows an area for work while traffic thunders overhead. The panels are made up of precast concrete and were placed during nights and weekends, the only time 53rd Street was allowed to close.

However, the decking system only provided for 17 ft. of headroom, said Norm Hirsch, project manager for Slattery/Gottlieb Skanska. The low headroom forced Underpinning & Foundations Constructors Inc. of Maspeth, N.Y., the project's foundation contractor, to modify a piece of equipment to fit in the provided space, said Ed Forte, the firm's vice president. "Some of this work was done from street grade and (some) below grade," he added.

Sorting out utilities was also a concern. Urs Bammert, project manager for Urbahn Associates, the project's architect, said maintaining service to the surrounding buildings, which include the Citicorp Building, the Lipstick Building and Memorial Sloan Kettering, was paramount.

"There was a sewer line right where we wanted to place the elevator," he said. In addition, a water main had to be spilt into two temporary pipes to supply water to the surrounding buildings.

A Difficult Dig
After the decking system was installed, crews began the excavation for the escalator and elevator. The constant threat of water infiltration was met with a secant pile wall, which acts as a cofferdam. To construct the wall, a modified drill bit was attached to a drill that can operate in low headroom, Hirsch said.

Then the machine drilled out a shaft that was 34 ft. deep to bedrock, which was then filled with concrete. The process was repeated until the desired dimensions were achieved.

Forte said that during drilling, "some old timber and concrete structures were encountered, so we had to drill through them and maintain the integrity of the wall."

After the secant wall was in place, crews began the process of excavating down to the platform. Once they reached bedrock, they had to dig by hand.

By late March, Slattery/Gottlieb had completed the excavation and was starting work on the mezzanine. "The goal is to get the new escalator in service by Oct. 15," Hirsch said. "We are working overtime and extra shifts to get this escalator open."

When crews reached the subway tunnel roof, extra care was taken to preserve the integrity of the arched roof, Bammert said. In addition, an extensive monitoring system was deployed to ensure against excessive vibrations from impacting the surrounding structures.

Mezzanine to Ease Crowding
The main push, the creation of the 200-ft.-long, 25-ft.-wide, 8-ft.-high mezzanine to connect the Third Avenue and Lexington Avenue ends of the station, began to be put in place in March. The result will allow passengers to transfer to the No. 6 line at any point in the station.

Ranabir Sengupta, a senior associate with Urbahn Associates Inc., said a serpentine wall will run down one side of the mezzanine and will introduce some curves to the otherwise boxy forms of the city's subway system. "We wanted to create a sense of space," he added. "We devised a curved wall that will create a sense of fluidity."

He said that the curved wall will be covered by artwork created by Al Held, a New York-based artist whose work has been shown at the Whitney. Held was brought on by the MTA's Arts-for-Transit program, said Sengupta. The Arts-for-Transit program has brought in numerous artists to design artwork that is being placed throughout the subway system.

There will be room next to the serpentine wall for mechanical equipment for the escalators and retail space, Sengupta said.

In addition to the work being performed for the mezzanine, work on the platform will include replacing the tile on the platform, repainting the tunnel walls and installing new lighting.

Work is scheduled to be completed February 2005.