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Turbines issue spotted too late

Potential grouting problems affecting offshore wind turbine foundations could have been spotted much earlier if operators used more extensive monitoring equipment, an offshore expert told a recent meeting at the ICE.

Problems with the application of grout between the transition sections of the wind turbine towers and their monopole supports have caused them to slip downwards (NCE 22 April 2010). This problem could have been discovered earlier, he said.

“Problems with the grouting could have been spotted earlier with more increased monitoring,” said Per Sparrevik an expert adviser with research firm Norwegian Geotechnical Institute (NGI).

He added that offshore wind operators would only consider monitoring after turbines have been installed.

Slippage problem

The slippage problem prompted Norwegian risk and certification firm Det Norske Veritas (DNV) to issue new guidance last year.

Original designs were for a vertical connection between the monopile and transition piece connected by grouting. DNV’s new recommendation is for a conical monopile and transition piece preventing any settlement (see diagram).
Sparrevik was speaking at a joint British Geotechnical Association and Offshore Engineering Society lecture on offshore wind turbine foundations.

The grouting problem hit wind farms across Europe, including UK fleets at Gunfleet Sands off the east coast, and Burbo Bank in Liverpool Bay at the mouth of the River Mersey.

After the meeting Sparrevik told NCE that there was very little monitoring of offshore wind turbines across Europe and data which could help improve designs was not being shared.

“I hope that wind farms being subsidised will encourage more sharing of performance data,” said Sparrevik, adding that this has not been the case in the offshore oil and gas sector.

 

Readers' comments (1)

  • Forget sharing performance data on wind farms, why did they not learn from the offshore oil/gas industry's use of shear connectors in the grouted pile/pile sleeve annulus. We have known for forty years that simply grouting a smooth sided annulus does not work.

    Secondly how will the expensive conical section resist the tension forces produced by the bending forces.

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