Dutzbo
The two largest caissons, which support the two main towers of the
bridge, are 100 feet by 190 feet, and weigh 16,000 tons each. The two
caissons for the flanking piers are 77 feet by 124.5 feet, and the
four smallest caissons are 46 feet by 100 feet. Each caisson is 40
feet high, and has exterior walls that are 34 to 45 inches thick.
The caissons were constructed in a natural clay pit at Grassy Point,
Rockland County, which is about 10 miles north of the bridge site.
This pit, which is 32 feet below the river's surface at its deepest
point, was the largest natural dry dock in the world. About 350,000
gallons of water were pumped out to permit construction of the
caissons. All eight caissons were transported by barge to the bridge
site, the first of which arrived on October 13, 1953.
Once the caissons arrived, they were floated into their exact position
by maneuvering them into a fender system built for each pier. Open
wells lined with corrugated, galvanized iron were run vertically
through the compartmentalized walls of the caissons. The caissons were
then filled with water and sunk atop a five-foot blanket of sand and
gravel about 42 feet below the river surface.
from
www.nycroads.com/crossings/tappan-zee/
