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AllWave-PDP Vibratory Driving Predictions Anholt Wind Farm

 

anholt kaartje

In January 2012 Dong Energy started the installation of 111 large mono pile foundations for the Anholt Offshore Wind Farm in the Kattegat sea in Denmark. The monopiles were installed with the heavy lifting vessel Svanen (Ballast Nedam), using a hydraulic impact hammer.  As regulations are becoming demanding regarding underwater noise emissions from pile driving activities, alternative pile driving methods and noise reduction measures are being considered. For this reason, Dong Energy is investigating the possibilities of using a large vibro hammers for the installation of the monopiles. Apart from noise aspects, the use of vibro hammers also offers better possibilities to meet the tolerance requirements, since a pile can easily be extracted and re-driven.

 

As part of this research, a full scale test with a vibrator on 2 of the monopiles was planned at Anholt. The test piles were 39-40 m in length, and had a diameter of 5.3 m (reducing to 4.9 m in the conical part at the top), a wall thickness varying from 45 to 65 mm and a weight of 270-280 tons. The piles had to penetrate 17-19 m into the seabed, that mainly consists of dense, calcareous sand.

 

Dong Energy hired Allnamics Geotechnical Experts to perform Vibratory Driving Predictions (VDP) for both test piles using the AllWave-PDP software program. After driving the piles DONG Energy provided allnamics with the installation records for post-analysis. These test results were very interesting, and confirmed that vibro hammers are suitable for the installation of monopiles, at least in sandy soil conditions similar to the Anholt project. Compared to the test results the VDPs  were generally on the conservative side, which provided us with valuable feedback to further improve our AllWave -PDP modelling.

 

More information about the project can be found at the official website:

http://www.dongenergy.com/anholt/EN/Pages/index.aspx

anholt vibrator anholt impact hammer

 

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