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Caisson foundations needed for next generation of wind farms, says expert

Future deep water wind farm developments and government targets will demand a different foundation design approach from the current monopile technique used in the UK, an Oxford University expert has said.

Oxford University lecturer Byron Byrne said monopile foundation construction was too expensive and time-consuming to allow government targets for wind energy capacity to be met by 2020, and other foundation designs would be more time and cost effective. Byrne was speaking at last night’s Geotechnique lecture at the ICE in London.

“Construction of monopiles for the turbines currently being installed is a costly and lengthy process and to meet government plans for 33GW capacity from wind by 2020, faster foundation solutions are needed,” he said. “To meet this aim around 800 wind turbines must be installed each year and a further 300 year will need to be replaced, so the industry needs to find an alternative.”

Byrne said mono or multiple suction caissons could be a viable alternative as they can be installed quickly. He said he was pleased that the Dogger Bank development was to use the system for its met masts. “While a caisson solution is not suitable for every ground condition, this approach will drive down the cost and time to build wind farms,” Byrne said. He urged developers to carry out field trials to prove the technology.

Wave, wind and load challenges

Byrne highlighted the issues of designing monopile foundations to cope with wave, wind and vertical loads imposed by the turbine and location.

He said future generations of wind farm projects would face increased challenges.

“Round 1 wind farms were relatively closer to shore but the current Round 3 developments are in deeper water. Round 4 sites are in deeper water still,” he said.

“The natural frequency of the pile must avoid the frequencies generated by the blades and the rotational frequency,” Byrnee said.

He went onto look at the issues related to the performance under cyclic loading of monopiles and the stiffness response to accumulated rotations from the various forces. He said these issues could have serious impact on fatigue in the structure and more field testing is needed to fully understand the potential problems.

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