How did they build the tunnels in NYC?

Tunnel workers (affectionately known as 'sandhogs') dug through the mud by pneumatically pushing cylindrical shields through the river bottom. Those shields held back the earth, making way for construction of the thick tunnel walls, built of cast iron rings filled with concrete.



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Today, underwater tunnels are often created with humongous tunnel-boring machines (TBMs) — sometimes called moles. These machines cost millions of dollars, but they can create large tunnels in a very short time. A circular plate with disk cutters rotates to cut through rock as the machine inches forward slowly.

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President Roosevelt broke ground for the tunnel on Oct. 2, 1936, by pushing a ceremonial button. During the next three years, the tunnel's two vehicle-carrying tubes were carved 10 stories below the surface of the East River, through Manhattan schist, limestone, gneiss and dolomite.

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Because they're stronger that way. Tunnels are circular to take advantage of the characteristics of soil and rock. Soil and rock are resistant to crushing forces (compressive forces). By rounding the ceiling, the weight of the soil and rock from the top to are balanced over the entire tunnel, increasing its strength.

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Because we dig while reinforcing them. Once a tunnel is dug, the walls are sprayed with concrete and immediately hardened. Also, steel frames called steel support and steel rods called rock bolts are used to reinforce the tunnel so that it can be dug without collapsing.

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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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Many of the disused subway stations and tunnels running under NYC are closed to the public for safety reasons, but there are still ways to see them. In some cases, you can catch glimpses of disused subway tunnels or subway platforms while riding past on currently operating lines.

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The Sandhogs of New York - out of sight and underground, the many Irish immigrants who dug as deep under the Big Apple as skyscrapers are high.

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“The first infrastructures of this type were built at the end of the 19th century, and at present there are nearly 200 underwater tunnels built worldwide. Although some are used for water and electricity supply, most are used to house road or rail connections.

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