A comprehensive pile testing campaign has been completed by Dong Energy and ESG, with initial results indicating potential cost savings for the offshore wind industry.
A total of 28 piles have been tested at two different onshore sites in order to assist the development of new design methods for offshore wind farms.
The testing is part of the Pisa (Pile Soil Analysis) research project, carried out by an industry working group including Dong Energy, EDF, RWE, Statoil, Statkraft, SSE, Scottish Power, Vattenfall, Alstom and Van Oord.
The testing has been undertaken to assess and validate a new design method developed by the Pisa academic working group, led by Oxford University and including Imperial College London and University College Dublin.
The academic working group supervised the testing on site, as each of the piles was pulled sideways into the soil until failure.
The 28 tests were conducted primarily investigating the static monotonic but also the response under cyclical lateral loading. During the largest test, the team simultaneously monitored more than 250 different precision instruments while applying a load greater than the weight of 37 London double decker busses.
The testing took place in Cowden, England and in Dunkirk, France. The clay till site in Cowden and the dense sand site in Dunkirk represent typical surface soil conditions found in much of the North Sea.
Both sites have previously been used for pile testing activities, mostly targeting oil and gas engineering, meaning that a rich amount of field and laboratory soil data is already available.
Alastair Muir Wood, lead geotechnical engineer at Dong Energy and technical manager for the Pisa project, said: “We’re very pleased with the test results, which confirm that traditional design methods in these soils are very conservative.
“The results indicate that in these site conditions there may be opportunities for savings identified by reducing the quantity of steel in the foundation. In other words, there’s a savings potential that will contribute to reducing the cost of electricity.”
Jesper Skov Gretlund, R&D project manager, added: “If the thickness or length of the steel piles can be reduced by even a small fraction, the saving in cost is quite considerable since smaller construction vessels can be used and larger turbines constructed.”
The academic working group will now analyse the data collected and use it to confirm the new design methods. The group’s final report is due to be delivered to the project partners in January 2016.