Experimental assessment of the insertion loss of an underwater noise mitigation screen for marine pile driving

Because of the concern about potential effects on marine pile driving, the industry is developing silent marine pile driving concepts. One of the new concepts, which has been engineered by IHC Hydrohammer in the Netherlands, is the application of a steel Noise Mitigation Screen (NMS) around the pile with the option of an additional confined air bubble layer. Initially, this mitigation measure was tested on a relatively small scale in shallow water (6-7 m depth), see [1]. The first results looked promising. In October 2011, IHC Hydrohammer and TNO tested a full-scale NMS in deeper water (25 m) during the pile driving of the foundations of two new meteo-masts (MM) with an IHC S-800 hammer (maximal blow energy: 800 kJ). Geometrical properties of the piles can be found in table 1. The two identical masts were installed at two different locations. One in Germany, North Sea Ost (MM-NO), and one in the Netherlands, off the IJmuiden shore (MM-IJM). At MM-IJM measurement were conducted during the complete piling process. At MM-NO, measurements were conducted during restrikes on a pile which had been installed several weeks earlier, at almost the required penetration. The objective of the measurements was to assess the acoustic insertion loss of the NMS in dB as a function of frequency in 1/3 octave bands. Further, the Sound Exposure Level (SEL) per strike in dB re Pa2s at 750 m range from pile driving was assessed to check compliance with German legislation (160 dB SEL, see [2])