Image source: lohud.com
The design-build team Tappan Zee Constructors that is building the Tappan Zee Bridge is installing the over 200-ft long steel pipe piles using a relatively simple concept to mitigate vibration impacts on fish – a bubble curtain. Such curtains have become more common as an approach to mitigate potential impacts (pardon the pun) on aquatic life when large piles are driven over water. The vibrations from the hammer impact on the pile during driving are reduced or dampened by a curtain of bubbles generated around the pile by compressed air. An item in the December 26th ASCE Smart Brief linked an article in The Journal News (White Plains, NY) highlighting the use of the curtain on the Tappan Zee project.
A rubber-looking sleeve covered the hammer where it met the pile, dampening some of the noise in the air. Underwater, however, it was a curtain of bubbles serving as the aquatic equivalent of earplugs for fish and other creatures in the Hudson River.
Aluminum rings are slid over the pilings like the rings on a shower curtain rod before any banging starts. Air pumped into the rings produces a sheath of bubbles in the water around the pile. The froth generated in the water is called a bubble curtain.
“Bubble curtains are designed to protect the fish in the area from the noise generated by the hammer impact below the water level,” said Walter Reichert, project manager for Tappan Zee Constructors. “This divides the water into basically two sections. It greatly reduces the sound waves.”