Fast installation of a suction pile foundation have been combined with the advantages of a lower costs monopile in a new foundation concept, according to developer SPT Offshore.
The Netherlands-based offshore contractor’s new system uses three or four suction piles at the base that connects with a mono tubular section that sits on top.
SPT Offshore has said that the mono tubular approach is three times less expensive than a jacket solution. The company also said that they are fast to install – generally taking three hours – and are virtually noise free.
“From our vast experience after having installed more than 500 suction piles, we know that suction piles are significantly optimised if smaller outer diameters are being selected compared to its depth,” said a spokesman for SPT. “This reduces the weight and improves its reliability and strength. Furthermore, in order to make suction piles more effective, the suction piles should be placed horizontally further apart, hence this load transfer from the mono tubular to the suction piles requires a transition piece.
“The transition piece can be built out of steel or concrete and we have not yet determined which material performs best. Concrete has it pros and cons, it is cheap to fabricate but is heavier for handling by a heavy lift crane vessel. Steel has the benefits of being light and simple to build and the design process is more flexible and allows a shorter fabrication schedule. On top of the suction piles and also on top or possibly inside the transition piece there is room for added ballast, which can be pre-installed or combined with rock scour protection measures after installation.
“Suction piles are suited for 99% of the North Sea and most shallow water areas worldwide having sandy, clayey or layered soils. We are further detailing the design right now and are working towards a demonstration in the next 12 months.”