Trench Cutter Case Histories and Their Possible Application for Offshore Piles as Relieve Drilling

As of 30th June 2013, according to the European Wind Energy Association, there are 1,939 offshore wind turbines, with a combined capacity of 6,040 MW. They are fully grid connected in European waters in 58 wind farms across 10 countries. About 70 % of the foundations used for wind energy are monopiles with a diameter up to 6 m. The monopiles are installed by using hammers. However, there are situations where the piles cannot be installed without the “driving and drilling technique”, above all in the glacial areas, where glacial tills, boulders or cobbles can be encountered. A new technology for supporting the installation of monopiles is the monopile-trench cutter. The following paper describes four onshore trench cutter case histories in hard geology. Based on several projects, a correlation between net cut performance and uniaxial compressive strength (UCS) values of the in situ rock is briefly described. The variation of the cut performance decreases logarithmically with increasing UCS values. However, the data showed are only based on projects already performed, and it is not possible to extrapolate the data for future projects in similar geological conditions. The findings of this paper want to show how the trench cutter technology might be a suitable technology for supporting monopile installation in difficult sea beds. Besides, the information contained in this manuscript wants to be an aid for contractors involved in offshore pile installation.