The underwater noise from impact pile driving was studied by using a finite element model for the sound generation and a parabolic equation model for propagation. Results were compared with measurements taken with a vertical line array deployed during tests at the Vashon Island ferry terminal near Seattle in November 2009. Tests showed that the dominant underwater noise produced by impact driving is from the Mach wave associated with the radial expansion of the pile that propagates down the pile after impact at supersonic speed.
The effectiveness of surrounding the pile in the water with a double-walled steel tube, also called a temporary noise attenuation pile (TNAP), to reduce the underwater sound caused by pile driving operations was also investigated. Tests and analysis showed that the noise attenuation capability of the TNAP was limited to approximately 10 dB because of the unconstrained propagation of Mach waves directly from the sediment into the water.