Largest ever testing of wind turbine piles completed
DONG Energy and ESG have just completed one
of the most comprehensive pile testing campaigns ever. Initial results
show great cost reduction potential for the offshore wind industry.
The two testing sites, located
in Cowden, England and in Dunkirk, France, carried out tests on 28 piles
in order to assist the development of new design methods for offshore wind
farms. 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.
Furthermore, 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.
The testing has been undertaken
by the joint industry project PISA and was performed 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 28 piles were pulled sideways into the soil until failure.
Alastair Muir Wood, Lead Geotechnical
Engineer 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."
Bladt and Dansteel supplied
piles of three different diameters for the tests; the piles with a diameter
of 2 metres are some of the largest ever tested. During testing, other
instrumentation was used including fibre optic strain gauges installed
by Marmota Industries. In total, 28 tests were conducted primarily investigating
the static monotonic but also the response under cyclic lateral loading.
Steve Turner, Project Director
from ESG, who undertook the testing, said: "The
PISA project has provided some of the most challenging testing we've ever
undertaken. With the largest test, we were simultaneously monitoring more
than 250 different precision instruments, whilst applying a load greater
than the weight of 37 London double decker busses."
The PISA academic working group
now has six months to analyse the data collected and use it to confirm
the new design methods. Their final report is due to be delivered to the
project partners in January 2016.
Jesper Skov Gretlund, R&D
Project Manager at DONG Energy, said: "The
PISA Project is a great example of inter-industry collaboration to solve
a common problem. 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 next challenge is to analyse all of the data collected in order to
refine our methods and apply these findings to our foundation designs."
This testing has been undertaken
as part of the research project PISA (pile soil analysis), which is
being carried out by an industry working group headed by DONG Energy and
involving EDF, RWE, Statoil, Statkraft, SSE, Scottish Power, Vattenfall,
Alstom and Van Oord. PISA is being run under the framework of the Carbon
Trust Offshore Wind Accelerator (OWA).