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United Kingdom

United Kingdom

Gallery: Pile testing that suggests monopiles could use 35% less steel

UK: ESG, a testing and compliance group, has set up new design codes and synchronised up to 220 separate instruments to create offshore monopile load testing with the potential to significantly reduce costs.

  • UK testing firm ESG designed new load tests for monopiles, for the Carbon Trust's Offshore Wind Accelerator Pile Soil Analysis project

    UK testing firm ESG designed new load tests for monopiles, for the Carbon Trust's Offshore Wind Accelerator Pile Soil Analysis project

  • The site in Dunkirk northern France features dense sand ground for the tests

    The site in Dunkirk northern France features dense sand ground for the tests

  • The site in Cowden, north-east England provided stiff clay soil. Both soil types replicate soil types in the North Sea

    The site in Cowden, north-east England provided stiff clay soil. Both soil types replicate soil types in the North Sea

  • Hydraulic rams and high level instrumentation on 2m diameter pile, simulating the lateral force of waves or wind

    Hydraulic rams and high level instrumentation on 2m diameter pile, simulating the lateral force of waves or wind

  • A medium pile of 0.762m diameter and large 2m diameter pile undergo forces of later load through a cable

    A medium pile of 0.762m diameter and large 2m diameter pile undergo forces of later load through a cable

  • Testing instrumentation for below seabed level - a total of 220 instruments were used during testing

    Testing instrumentation for below seabed level - a total of 220 instruments were used during testing

  • The instruments were placed on and in the piles, to allow validation of the results

    The instruments were placed on and in the piles, to allow validation of the results

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Working in partnership with Dong Energy as part of the Pile Soil Analysis (PISA) project, ESG conducted large-scale field testing of wind-turbine monopiles. A total of 28 scale-model monopiles of varying sizes were examined across two onshore sites with different soil types. The stiff clay soil of the site near Cowden, north-east England, and the dense sand ground of the other site near Dunkirk, northern France, replicated soil types found in the North Sea, said Dong.

The testing company developed new design codes for testing piles, using a wide range of tools such as retrievable extensometers and in-place inclinometers. The test rigs used hydraulic capability, data logging and synchronisation of up to 220 separate instruments for different loading conditions.

The project finished in September.

The project's technical manager, Alastair Muir Wood, said that the initial results from the campaign showed "traditional design methods in these soils are very conservative".

The test results suggested that 35% reduction in steel could be made, using reduced metal thickness and narrower or shorter monopiles in these soil types. This would make monopile foundations cheaper.

PISA was launched in 2013 through the Carbon Trust Offshore Wind Accelerator programme, a UK government-supported agency that promotes cheaper offshore wind power.

Oxford University was heading the investigation with support from Imperial College, London, and University College, Dublin. Industry backers included: Dong, RWE, Statoil, SSE and Scottish Power.

The data is undergoing further analysis.

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