The Slurry Wall — An Innovation At the Time

GEORGE TAMARO: An Italian innovation, slurry walls were first used in 1949. The Port Authority was very courageous to use them in 1967, since slurry walls had not previously been used to this particular extent. The first step was to excavate a slot in the ground several feet across that ultimately formed the shape of the reinforced concrete wall. Using a clamshell bucket, we excavated soil from within this slot, replacing the ground with a mixture of clay and water, which kept the slot from collapsing. When we got to the top of the bedrock, we chiseled a key into the rock at the bottom, giving us a watertight connection. We then installed a reinforcing steel cage into the slot.

Once the cage was secured in position, we put concrete into a hopper at the top of a long "tremie" pipe that extended down to the bottom of the slot. As we placed concrete into the slot forming a panel, we drew slurry out of the slot, reversing the initial excavation process; the three-foot concrete wall panel then hardened in the ground. During excavation, the face of the wall was exposed one level at a time. To support the wall against pressure from the water, soil and streets, we drilled steel tieback tendons through the wall, down 100 feet to the rock, and then 35 into the rock for an anchorage. Later, we cut the tieback anchors and buried them within the wall once the new basement slabs were installed and the floor system could support the slurry wall.

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