Underwater sound characteristics from down-the-hole pile drilling for a coastal construction activity

Abstract

Sound generated by pile installation using a down-the-hole (DTH) hammer is not well documented and differs in character from sound generated using conventional impact or vibratory hammers. This study describes underwater acoustic characteristics from DTH pile drilling during the installation of 0.84-m shafts within 1.22-m steel piles associated with a cruise ship terminal construction in Ward Cove, Alaska. The median single-strike sound exposure levels measured at 10 m were 138 and 142 dB re 1 μPa2s for each of the two piles, with cumulative sound exposure levels of 188 and 193 dB re 1 μPa2s at 10 m, respectively. The sound levels measured in this study were significantly lower than previous measurements of DTH pile driving, and the sound is determined to be less impulsive in this study as compared previous studies. These differences likely result from fact that the DTH hammer used at Wade Cove did not make direct contact with the pile, as had been the case in previous studies. Further research is needed to investigate DTH piling techniques and associated sound-generating mechanisms and to differentiate the various impulsive structures from anthropogenic underwater noise in general.