How did they build the subway under the East River?

William Parsons, the project's chief engineer, used a variety of techniques for underwater digging. Sometimes hydraulic shields were used; other times methods were improvised, like digging a trench in the riverbed, then sinking the tunnel roof down on top of it.



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The work was primarily done by open excavation, also called the “cut-and-cover” system. The typical subway route (called “road” in this text) was built near the surface with a flat roof and “I” beams for roof and sides and supported between tracks with columns.

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Large portions of the subway outside Manhattan are elevated, on embankments, or in open cuts, and a few stretches of track run at ground level. In total, 40% of track is above ground. Many lines and stations have both express and local services.

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Most tunnels are lined with something like stone or concrete that is strong in compression (i.e. something that can be squeezed a lot without crushing).

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The project began in 2013 with the excavation of two vertical shafts in Newburgh and Wappinger to gain access to the subsurface. These shafts, 845 and 675 feet deep respectively, were completed in 2016. A massive tunnel boring machine completed excavation of the tunnel on Aug.

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NYC Transit assistant chief of the Division of Stations Branko Kleva told Slate that the mysterious black gunk is actually a material called mastic, which the city has used to seal and waterproof the tunnel structures.

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It is the first tunnel known to have been constructed successfully underneath a navigable river. It was built between 1825 and 1843 by Marc Brunel, and his son, Isambard, using the tunnelling shield newly invented by the elder Brunel and Thomas Cochrane.

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The four lines under the river are numbered south to north, lines 1 and 2 running beneath 32nd Street and Lines 3 and 4 under 33rd Street.

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THE world's first metro, now the world's oldest system, is the London Underground in England, which is more commonly known as the Tube, which was opened in 1863. At 402 kilometers in length the London Underground is also the world's second longest metro system.

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The Shanghai Metro is the world's longest metro network at 803 kilometres (499 mi) and has the highest annual ridership at 2.83 billion trips. The New York City Subway has the greatest number of stations with 472.

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In addition to the 665 miles of active subway tracks running beneath the city, the concrete hides an entire world of secret tunnels and subterranean spaces. If you dare to venture where the sun doesn't shine, some of these hidden worlds are open to explore on guided tours. Why does New York City have secret tunnels?

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