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Case Studies: Current Projects

Extensive Conveyor System Crosses New York Highway

Project Overview

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 (the ‘Tunnel to Nowhere’) will become operational when the East Side Access Project is completed in 2013.

The project, awarded to the Dragados/JudlauJV, is located in a range of geology from soft ground to hard rock. Twin 13.7 km (8.5 mi) long Manhattan Approach Tunnels will 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, currently excavating the Westbound tunnel, will bore two headings on the project, requiring a design that allows for swift retraction and re-launching. The machine will bore 2.6 km (1.6 mi) towards Grand Central Station, and will then be retracted 2.0 km (1.2 mi)through the newly bored tunnel, leaving all tracks and tunnel support structures in place. The machine will then be re-launched at a “Y” shaped intersection to bore another tunnel at a slightly higher elevation.

The Robbins High Performance (HP) Main Beam machine has been designed using a segmented, bolt-only cutterheadfor swift disassembly. For retraction, the outer components of the cutterheadwill first be removed. The shielded front section of the TBM, designed as an “umbrella”, can then be retracted using hydraulic extensions. The extensions allow 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 involves nine separate conveyors handling muck simultaneously from the two tunnels. Two extensible fabric belt conveyors (914 mm/ 36 inches in width) travel behind the Eastbound and Westbound TBMs, and dump 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 is transported up the 23 m (75 ft) deep Queens shaft using a fixed-length, steel cable vertical conveyor. Once the muck has reached the top of the shaft, it is transferred to the Rail Yard using three overland conveyors and a radial stacker. The second overland conveyor, 37 m (120 ft) in length, crosses 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 sits approximately 6 m (20 ft) above Northern Boulevard and under pre-existing rail lines. Muck is then transferred from the overland conveyors to a radial stackerin the Sunnyside Rail Yard. The radial stacker can then rotate through 60 degrees to deposit muck in kidney-shaped piles with a capacity of 8,400 cubic meters (11,000 cubic yards).

Updates of this project will be posted as boring continues.

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