Traylor Bros., Inc. led the second largest contract in the system of tunnels being constructed to connect the Long Island Railroad (LIRR) commuter lines in Queens to Grand Central Station in Manhattan. Presently, the line only connects with Penn Station; the additional 24 peak-hour LIRR trains into Grand Central represent a capacity increase of about 30,500 new peak-hour seats, meeting the future needs of Long Islanders to reach Manhattan jobs.
The scope of work for the project included the construction of four 19-foot-inner-diameter railway tunnels totaling approximately 2 miles in length, three reception pits, and three shafts that included cross passages for emergency access and ventilation. The tunnels, comparatively shallow (between 20 and 70 feet below the surface), are located beneath the Sunnyside Rail Yard in the borough of Queens, New York City. The project connects the existing 63rd Street tunnel, using the open-cut structure created by the Queens open-cut excavation contract, to the mainline LIRR tracks. Two 22.5 foot Herrenknecht slurry TBMs were used in the difficult geological conditions, which included full face of granitic rock, mixed face of rock and soft ground, and full face of soft ground. The soft ground was mainly a dense glacial till containing numerous cobbles and boulders. Hyperbaric interventions were utilized for cutterhead maintenance, along with one frozen-ground Safe Haven. A one-pass precast concrete segmental lining was installed in the tunnels. A single three-compartment cross passage was constructed between two of the tunnels using Sequential Excavation Methods.
The most challenging aspect of the project was dealing with the highly variable ground conditions, which could have resulted in settlement beneath the active tracks of the rail yard. The team controlled settlement by using a slurry TBM system.