Early Dutch settlers landed near today’s Greenwich Street in 1614, on a shoreline that has since shifted outward through centuries of landfill. When the World Trade Center was built in the 1960s on this former Hudson River bed, engineers had to prevent river water from flooding the site. They used an innovative Italian technique—the slurry wall—on a scale never before attempted in the U.S. Crews dug 70-foot-deep trenches, filled them with bentonite slurry to hold back groundwater, then inserted steel cages and concrete to form 158 interlocking panels. Tie-back anchors were drilled into the bedrock as excavation progressed, creating the vast waterproof “bathtub” that made construction of the Twin Towers possible. The project set a new benchmark in foundation engineering and helped establish slurry walls as a standard technique worldwide.
