The Lincoln Tunnel remains one of the defining achievements of 20th-century civil engineering, carrying traffic between Midtown Manhattan and Weehawken, New Jersey, beneath the Hudson River. Originally known as the Midtown Hudson Tunnel, the project required engineers to solve a difficult combination of problems: soft riverbed silt, water pressure, sections of rock near the approaches, the health risks of compressed-air construction, and the buildup of automobile exhaust inside a long underwater roadway.
The first tube was built under the direction of Port Authority chief engineer Othmar H. Ammann, with Ole Singstad serving as chief tunnel consulting engineer. Singstad brought crucial experience from the Holland Tunnel, where he had helped develop the ventilation system that made long underwater vehicular tunnels practical. Construction on the first Lincoln Tunnel tube began in 1934. That center tube opened in 1937, followed by the north tube in 1945 and the south tube in 1957.
The Tunneling Shield and the Hudson River Silt
Much of the riverbed along the Lincoln Tunnel alignment consisted of soft mud and silt, although workers also encountered rock near the approaches. Engineers could not simply excavate an unsupported passage beneath the river. Water and saturated soil placed continuous pressure on the work area, creating the danger of flooding or collapse if that pressure was not controlled.
The solution was shield tunneling combined with compressed air. A huge circular steel shield protected the men working at the tunnel face while hydraulic jacks forced the shield forward through the earth. The Port Authority described the jacks as producing a combined thrust of approximately 6,000 tons. In the soft riverbed, the shield could push directly through the silt. Where crews encountered rock, workers drilled holes, loaded explosives, blasted the rock, and removed the debris before the shield could advance…