4. The Manhattan Tower of the Brooklyn Bridge Sits on Sand
Each of the Brooklyn Bridge’s two massive granite towers weigh an incredible 90,000 tons each. In order to reach the bedrock below the river mud, massive caissons, basically giant diving-bells, were built to enable workers to excavate the tower foundation sites underwater. The top of these structures were made of 22 feet of pine fastened by bolts and pitch. The workers entered and exited the caisson via a primitive airlock.
As opposed to the Brooklyn side bedrock the New York side bedrock proved to be much deeper than originally estimated. As work approached nearly 80 feet down excavation had to stop, even though bedrock lay at least another 20 feet down. Far too many men were becoming ill with the feared caissons disease, better known today as the bends. Men suffered from joint pain, itchy skin, seizures, vision problems, and some suffered various levels of paralysis and eventual death.
The granite blocks making up the towers were laid right on top of the caissons. The 90,000 ton weight of each tower and the concrete poured inside each caisson squeezed the wood of the caisson roof making it waterproof and impervious to rot. Technically the Brooklyn tower rests on bedrock, while the Manhattan tower does not! The Chief Engineer and son of the Bridge’s architect, Washington Roebling, noted that the sand that the Manhattan tower’s foundation rests on had not shifted in millions of years and probably wouldn’t for millions more.