Dredging and operations of a heavy-duty deepsea quay wall for offshore wind energy
CEDA Dredging Days 2017 - Sustainable Dredging - Continued Benefits
Putteman J., Broos E.J., Bosschieter C.G., Tuunter L.T.C.
Abstract: Due to the increasing demand for offshore wind energy in Western Europe, a new terminal is built at the Maasvlakte 2 in the Port of Rotterdam (the Netherlands) to expand the production and storage capacity of the market leader in the production of monopiles (foundation elements) for wind turbines. The terminal is referred to as the Offshore Terminal Rotterdam. The 500 meters long deepsea quay wall consists of a 18 meters wide concrete relieving floor and a substructure comprising a combined wall, concrete foundation piles and 60 meters long steel tension piles. The quay wall is built on the crest of an embankment which is subsequently removed by means of a trailing suction hopper dredger. The quay wall is designed for the largest jack-up vessels operating in the North Sea. As the penetration and extraction of the legs of the jack-up system pose a potential threat for quay wall stability, extensive analyses of measured spudcan penetration are performed based on bathymetric surveys. Furthermore, the impact of the spudcan on the subsoil is assessed by cone penetration testing (CPT). In order to limit spudcan penetration near the quay wall, a 8 meters thick clay layer is dredged and replaced by a vibro compacted sand fill. The clay removal is the most challenging part of the dredging works, as the clay has to be removed as deep as NAP -30.00 m and one jacking position is simultaneously available for operations. The suitability of the sand fill for vibro compaction is compared to literature. The quality control procedure of the compaction process is based on cone penetration testing. CPT results before and after compaction are compared. With cone resistance values well above 30 MPa, vibro compaction proved to be successful.
Key words: offshore terminal, spudcan penetration, soil replacement, vibro compaction