Retractable Robbins TBM will burrow under Manhattan

The TBM will bore the Westbound Manhattan Approach Tunnel for the Metropolitan Transportation Authority's East Side Access Project. Twin rail lines will cross the East River via an existing submersible tube tunnel to accommodate increasing commuter demands between the areas of Queens and Manhattan.

Located in the middle of the city, the 23 m (75 ft) deep Queens shaft will serve as a portal for delivery of the Robbins TBM, as well as another hard rock machine boring the eastbound tunnel. The Robbins machine will be partially assembled at the bottom of the shaft, while final assembly of the machine will take place in an underground assembly chamber on the Manhattan side after being transported approximately 1.8 km through the submersible tube. Once the machine has bored an initial heading, the TBM will be de-mobilized and retracted to excavate a second heading running up to Grand Central Station.

In order to accomplish the mobilization/demobilization, the machine has been supplied with specialized features. A five-piece, bolt-only cutterhead design requires no welding for swift disassembly, while hydraulically positioned front, side, and roof supports can be retracted during TBM removal.

The expandable components allow the TBM to fluctuate from a 6.136 m (20.1 ft) diameter when fully retracted to 6.906 m (22.6 ft) when fully extended. The design will ease transport of the machine through varying cross sections of tunnel and through the smaller-diameter submersible tube. Once the TBM has been transported back into the assembly chamber, it will be re-launched approximately 305 m (1,000 ft) away from the first bore.

Muck will be removed from the site by a system of continuous conveyors, also supplied by Robbins. The system will transport muck via three overland conveyors to a storage site 366 m (1,200 ft) away. One of the overland conveyors (37 m/ 121 ft in length) will cross Northern Boulevard, a main thoroughfare. The conveyor will be designed as a totally-enclosed box truss with 152 mm (6 inch) wide flange beams at all four corners to support the structure 6 m (20 ft) above the roadway and under existing elevated rail lines.

Rock in the tunnels consists of Manhattan schist with gneiss from 80-200 MPa (11,600 to 29,000 psi) UCS. Groundwater infiltration is expected to be limited, though the tunnel will pass through two fault lines. Tunnel support will consist of cast-in-place concrete lining in weak areas, as well as steel ribs, rock bolts, and wire mesh depending on the geology.

Overall completion of the Manhattan Approach tunnels is expected to take about one and a half years. The completed East Side Access line is scheduled to be operational by 2013.

Contact information:
The Robbins Company
29100 Hall Street
Solon, OH 44139
USA

Brianna Home
Marketing Director
phone: +1 253.872.4484
eMail: homeb@robbinstbm.com
Web: http://www.robbinstbm.com

Desiree Willis
Technical Writer
phone: +1 253.872.4490
eMail: willisd@robbinstbm.com
Web: http://www.robbinstbm.com