The importance of the geophysical survey for a Wind Farm

Today we speak about geotechnics…yes!, geotechnics, that activity that sometimes sounds strange but is so essential for the development of a proper wind farm project.

More specifically, we will see in detail tomographic refraction tests and MASW analysis.

This information is key for wind turbine foundation design but also can be needed for several other activities, such us for instance estimation of excavation (earthworks cost is linked to the hardness of the materials) and seismic design.

Geophysical works for a Wind Farm in Egypt, 2021
Geophysical works for a Wind Farm in Egypt, 2021

The analysis of the elastic modulus had been typically done with laboratory tests until a few years ago, when geophysics techniques began to be widely implemented (sometimes with unclear goals and misunderstood results).

The main advantages of these on site tests are:

  • Characterization of real terrain conditions taking into account the large magnitude of the structure it will support and its three-dimensional behaviour, rather than extracting small samples that could be not representative of the system as a whole
  • The possibility to obtain the dynamic parameters of soil stiffness, which are often the dimensioning factor due to the need to achieve a certain rotational rigidity for the wind turbine

It is important to highlight that some soils don´t seem to be apt to withstand the ever-larger loads of today’s wind turbines if they are tested using “classical” methods (odometer, triaxial, etc…).

However, the same soils show a better performance when geophysical techniques are used to analyse them, mainly because they are less conservative, more realistic and more appropriate for dynamic loads and quite relevant foundation dimensions.

One more comment on dynamic parameters of soil stiffness: it´s worth noting that correlations that were widely used to estimate dynamic values from static values used to imply, depending on the type of terrain, wide uncertanties.

In some cases the values were unfavourable and did not allow to optimize the dimensions of the foundation. In others cases, unrealistic values reduced the level of safety in designs.

For all these reasons geophysical survey is strongly embedded in the way wind turbine foundations are currently designed, so the IEC 61400-6:2020 has made changes in its latest edition (see Annex L) to improve and adjust the calculation methodology.

Variation of shear modulus with soil strain

As a summary, take into account that optimization and accuracy within geotechnical calculation can lead into an optimization of the foundation, so be aware of the importance of geophysical survey for a wind farm and opt for a more comprehensive geotechnical study, appropriate to each case, modern and based on international regulatory updates.

3 responses to “The importance of the geophysical survey for a Wind Farm”

  1. Sue Page Avatar
    Sue Page

    There is currently a proposed wind farm project called Lava Ridge in Southern Idaho. 25 miles northeast of Twin Falls, Idaho. The plan is for 400 740ft tall wind turbines, over 400 miles of roads, transmission lines and buildings.

    Citizens are considered as the Environmental Impact Statement doesn’t have any testing to show the land can withstand this project.

    The area is on top of the Snake River Plain Aquifer which is part of the Volcanic Geographical Axial spanning westward from Yellowstone westward through the volcanic areas of The Craters of the Moon, Wilson_Butte_Cave and into Salmon Falls and Thousand Springs..
    It is the high desert with winds, heat and snow.

    There isn’t any testing planned until after the BLM grants the company, LPPower, a lease.

    They have advised there will be blasting twice a day for over 500 days. There will be the vibrations from the heavy-duty equipment, the wind turbines themselves and how will the Lava strata hold up. We think it will crush the Lava tubes, contaminate the sole source drinking water for Southern Idaho.

    What’s your opinion? What testing should we require?
    Any help would be appreciated
    Thank you
    A concerned citizen of Southern Idaho

  2. Echo Stuhlberg Avatar
    Echo Stuhlberg

    My biggest concern is what damage will be done to the aquifer. There has not been enough studies done on how it would affect the aquifer. If the blasting closes off the aquifer there would be no water in Jerome and Gooding counties from the wind farm to the canyon at Thousand Springs.

  3. Hi Lift Cranes Avatar

    Uncategorized may be the category, but the importance of wind farms in our sustainable future is anything but uncertain. These impressive turbines harness the power of nature, providing clean and renewable energy. They are testaments to human ingenuity and our commitment to reducing carbon emissions. Let’s continue to explore and embrace innovative solutions that make wind power a key component of our global energy landscape.

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