Measurements of Pile Driving Noise from Control Piles and Noise-Reduced Piles at the Vashon Island Ferry Dock: Fid-Bau Portal

Measurements of Pile Driving Noise from Control Piles and Noise-Reduced Piles at the Vashon Island Ferry Dock

D. R. Dall’Osto / J. Laughlin / P. H. Dahl

As part of the Washington State Department of Transportation (WSDOT) pile attenuation test program, researchers from the University of Washington Applied Physics Laboratory (APL-UW) conducted underwater sound measurements on 7 and 8 December 2015 at the Vashon Island ferry dock. A WSDOT team operating closer to the construction barge also took measurements. The goals of the APL-UW team were to measure the underwater sound field over nearly the entire water column and away from interfering structures, as well as to make robust estimates of sound mitigation performance of two test pile designs in terms of sound exposure level (SEL) and peak pressure. Measurements on the R/V Robertson were taken at a range of 120 m from the construction barge complex and pile source location and at a water depth 12.5 m by using a vertical line array (VLA) that spanned 1.25 to 9.25 m in depth. A comparison of the 7 December measurements from the double wall test pile with the control pile showed reductions in peak pressure (8.7–13.5 dB), RMS pressure (8.8–12.7 dB), and SEL (7–10.3 dB). A comparison of the 8 December measurements from the mandrel test pile with the 7 December measurements from the control pile showed reductions in peak pressure (11.4–14 dB), RMS pressure (10.8–12.6 dB), and SEL (9.3 and 11.1 dB). The reduction in peak pressure generally increased as measurement depth on the VLA increased; for the RMS and SEL metrics, no trend was observed.