In 1614 early Dutch settlers of Manhattan landed on the shoreline of the Hudson River near what is today Greenwich Street, just east of the 9/11 Memorial & Museum. Over the past 400 years, Manhattan’s footprint has expanded outward, having been filled during various periods of development with demolition debris, marine construction, abandoned ships, and city waste.
As construction of the World Trade Center was commencing in the 1960s at a 16-acre area of landfill known as Radio Row, the Port Authority of New York and New Jersey had to determine a way to build the two largest skyscrapers in the world on a site that was once submerged within the Hudson River. The solution to this challenge was to employ an innovative Italian construction technique—never before used at this scale in the United States—known as the slurry wall method. This involved building an underground perimeter wall that would stop the entry of river water into the site and permit excavation down to bedrock, where the Twin Towers’ foundations would be built.
The slurry wall method was patented in Italy in the late 1940s by the ICOS Company. It was then introduced during construction of Milan’s subway system in the 1950s. The technique was brought to the United States in the 1960s and used on small projects before being employed at a larger scale for the construction of the World Trade Center in 1967.