2008 Recipient:

The Dey Street Tunnel Project is a Design Build project which connects two transportation hubs – the new PATH station at the site of the World Trade Center and the New York City Transit (NYCT) Fulton Street Transit Center – with a tunnel beneath Dey Street in lower Manhattan and creates two new concourses beneath two existing subway stations. Upon completion, the Fulton Street Transit Center will help streamline the connection between 10 NYCT subway lines.

The challenges of the Dey Street Tunnel project included underpinning and excavation below two active subway stations (600 linear foot total) for construction of the concourses; design and construction of floating concrete slabs to serve as support for the train and street loads, one in particularly difficult ground; installation of secant pile walls adjacent to historic and prominent buildings in a congested urban working environment; construction of a 300-foot long, cut-and-cover tunnel beneath an active city street; and related challenges working with existing structures that are over 100 years old.

The signature piece of the Dey Street Tunnel Project is a 300-foot long concrete tunnel beneath Dey Street between Broadway and Church Street in lower Manhattan that will connect the PATH Station and the NYCT Fulton Street Transit Center. Originally designed as a steel bent structure, the design-build team developed an alternate design using a reinforced concrete tunnel as a better, more efficient way to design and build the tunnel. With a 29’ width and 17'-9" height as the standard dimensions, a concrete tunnel was more flexible when encountering a "notch" to avoid existing building vaults and a 15' depressed section was included to accommodate existing utilities.

One of the unique challenges for the Dey Street Tunnel project was underpinning and excavating below two active subway stations without interrupting the weekday train schedules, all while meeting the aggressive construction schedule proposed by NYCT. The Fulton Street Station on the Lexington Avenue Line was originally constructed in the early 1900s, and the Cortlandt Street Station on the Broadway Line was placed in service in 1918. Both stations' invert slabs rested on grade and were underpinned with minipiles installed with the station structures using low head room rigs. In order to maintain regular train service, Skanska had to perform the work during 55-hour track outages on consecutive weekends. Due to the aggressive schedule, the design-build team came up with an innovative top down approach for underpinning the subway lines by installing the permanent track slab as part of the temporary underpinning of the subway. The use of 8,000 psi high early concrete for the track invert slabs was one of the reasons the contractor was able to meet the project schedule and to have trains running at 5 am on Monday morning.

Below the underpinned subway stations are two new concourses 300 feet by 100 feet. To support the subway and street loading, each station uses 5 foot floating slabs. Originally designed as pile supported mats, the design team used floating mats to support the underpinning structure, results in the savings of both cost and construction time.

The Dey Street Tunnel is an integral part of the Fulton Street Transit Center, which in turn is a major component of effort to rebuild and revitalize lower Manhattan. The tunnel should open for use in November of 2012.

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