Noise from the installation of offshore wind turbines could be reduced by 90-95% thanks to a new method.
Dutch installation specialist GBM Works is developing the technique to reduce the noise pollution caused by driving foundation piles into the seabed.
The method involves ‘fluidising’ the seabed with water jets, which ensures the monopiles sink much quicker and with significantly less noise.
“Driving foundation piles for wind turbines into the seabed causes vibrations, pressure waves and – in particular – also a great deal of noise,” said Ben Arntz, founder and director of GBM Works. “When a steel foundation pile with a diameter of eight metres is driven, the noise production can reach a level up to 180 decibels. The vibrations, the pressure waves and the loud noise have a negative effect on underwater life… International guidelines are expected to become stricter in the coming years. Our new method responds to this.”
As part of the new technique, dozens of water jets spray seawater into the seabed. Its consistency becomes similar to “quicksand”, Arntz said, decreasing its resistance and allowing the foundation pile to sink into the seabed.
A vibratory hammer also replaces the hydraulic pile-driving rig, which is used in conventional installations and causes considerable noise as it strikes the steel foundation. The vibratory hammer consists of rotating disks mounted on top of the monopile, which vibrates and sinks into the fluidised ground.
The new system was tested at Maasvlakte port in the Netherlands. Sixty-two test installations were done with four set-ups – two with the jet gun system and the vibratory hammer, and two with the vibratory hammer alone. Strain gauges were supplied by testing specialist HBK to measure the vibrations and deformations of the monopiles.
“Most of the data now has been analysed,” said Wouter Verschueren, data and model engineer at GBM Works. “We saw, for example, that the foundation piles with the vibratory hammer alone penetrated the ground no further than three or four metres because the soil resistance became too high.
“With the jet gun and the vibratory hammer, the piles easily went to a depth of 10m, while the speed at constant force quadrupled. In a subsequent test cycle underwater, the noise production of the solution with the vibratory hammer and the jet gun will be compared to that of a traditional pile hammer. A pile-driving rig in combination with a sound mitigation system is currently used.
“These are complex systems that operate with an underwater shield around the foundation pile to damp the vibrations and noise. GBM Works expects a noise reduction of 90-95% thanks to the new system.”
GBM Works recently received a subsidy of €1.8m from the Netherlands Enterprise Agency for the development of a prototype of the equipment.
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