The project’s signature features include the construction of GCM station caverns, concourse and the connecting high-rise escalators, which are adorned with beautiful glass, marble finishes and arches that replicate the aesthetics of the historic GCT.
The station caverns required blasting under GCT to enlarge bored tunnels and create two 60-foot-wide by 80-foot-deep caverns, which are separated from the lower level of GCT by approximately 40 feet of rock. The 350,000-square-foot passenger concourse was created from extensive reconstruction of GCT’s western lower-level track area, where existing structural elements were reframed to create space for the high-rise escalators.
“WSP’s primary role was to provide geotechnical and structural design and construction support for the station caverns and high-rise escalator shafts.” Cicileo said.
Several innovative tunneling and ground treatment techniques were employed for this project, including the first full-sized, soft ground pressurized face TBMs used in the New York area.
“These tunnels pushed the limits of soft-ground TBM operation to minimize the need for cut and cover construction in Harold Interlocking,” said WSP’s Jeff Rice, GEC’s former deputy director and lead structural engineer.
The Northern Boulevard Crossing tunnel was the first in the area to use ground-freeze methods and the sequential excavation method, and various ground treatment methods were used to support the Queens tunneling. Then there’s the Manhattan tunneling work, which included innovative uses of tunnel drives to minimize drill and blast operations.
Extensive monitoring and state-of-the-art drill and blast techniques resulted in efficient material removal, and no impact to the surrounding infrastructure.
“The project was constructed with minimal impact to the community,” Cicileo said. “The Manhattan side of the project has been likened to orthoscopic ‘keyhole’ surgery, with minimal impact at Grand Central Terminal and limited construction traffic in Manhattan.”
A primary illustration of this is the removal of rock removed from the tunnels and station caverns. Instead of removing the rock onto the surface streets of Manhattan, the material was conveyed through the tunnels and directly into Queens, where its removal was much less intrusive to the community and to the Rail Road.
“The work in Queens was more visible, but the safety and performance of the railroads remained foremost considerations,” Cicileo added.