New York City’s East Side Access Project involves construction of a new subway line needed to relieve heavy traffic congestion between the boroughs of Queens and Manhattan. The line will serve approximately 160,000 commuters daily between Grand Central and Sunnyside rail stations.
Manhattan and Queens will be connected under the East River via the 63rd Street tunnel, a submersed double-deck tube. The submersed tube consists of reinforced concrete sections barged in place on the riverbed. The tube contains operational subway lines on the top deck, while the bottom deck will become operational when the East Side Access Project is completed in 2013.
The project, awarded to the Dragados/Judlau JV, is located in a range of geology from soft ground to hard rock. Twin 13.7 km (8.5 mi) long Manhattan Approach Tunnels run from the Manhattan side of the submersed tube up to Grand Central station, with geology consisting of schist, gneiss, and granite from 100 to 275 MPa (14,500 to 40,000 psi) UCS.
The Robbins TBM excavated the Westbound running tunnels, consisting of four short headings that required a design allowing for swift retraction and re-launching. A second Double Shield TBM, operated by SELI, was used to excavate the Eastbound running tunnels. The Robbins High Performance (HP) Main Beam machine was designed using a segmented, bolt-only cutterhead for easier disassembly. During retraction, the outer components of the cutterhead were removed first. The shielded front section of the TBM, designed as an “umbrella”, was then retracted using hydraulic extensions. The extensions allowed the bottom, side, and roof supports to move radially inwards, reducing the machine diameter from 6.7 m (22.0 ft) when fully extended to just 6.1 m (20.0 ft) with removal of the shield assemblies.
To remove muck, Robbins designed an extensive conveyor system utilizing every commonly recognized type of belt conveyor to transport muck more than 370 m (1,200 ft) away from the jobsite. The system design involved nine separate conveyors handling muck simultaneously from the two tunnels. Two extensible fabric belt conveyors (914 mm/ 36 inches in width) traveled behind the Eastbound and Westbound TBMs, and dumped via a crown-mounted cross conveyor onto a single 1,863 m (6,100 ft) fixed-length conveyor mounted inside the submersed tube.
From the tunnel, muck was transported up the 23 m (75 ft) deep Queens shaft using a fixed-length, steel cable vertical conveyor. Once the muck reached the top of the shaft, it was transferred to the Rail Yard using three overland conveyors and a radial stacker. The second overland conveyor, 37 m (120 ft) in length, crossed Northern Boulevard, a major thoroughfare in Manhattan. This conveyor was designed as a completely enclosed box truss to eliminate debris from reaching the roadway, and sat approximately 6 m (20 ft) above Northern Boulevard and under pre-existing rail lines. Muck was then transferred from the overland conveyors to a radial stacker in the Sunnyside Rail Yard. The radial stacker rotated through 60 degrees to deposit muck in kidney-shaped piles with a capacity of 8,400 cubic meters (11,000 cubic yards).
The Robbins machine made four drives, totaling 5.2 km (3.3 mi) beneath Manhattan. The machine first bored 2.3 km (1.5 mi) towards Grand Central Station, and was then retracted 2.0 km (1.2 mi) through the newly bored tunnel, leaving all tracks and tunnel support structures in place. The machine was re-launched at a “Y” shaped intersection to bore three more tunnels at varying elevations.
Boring on the first tunnel commenced on September 30, 2008 with a total of 907 boring hours, and the second, 540 m (1,770 ft) tunnel was finished on February 20, 2009 after 267 boring hours. A third 1.7 km (1.1 mi) long tunnel was completed in February 2010. By June 2010, the machine had completed its fourth and last 630 m (2,060 ft) long drive after 281 boring hours. The conveyor system operated at over 90% availability during the course of the four headings.
At the time of completion for the Robbins Main Beam machine, the SELI TBM was being readied to bore the third of its four Eastbound running tunnels.