What is a Geotechnical and Geophysical Site Investigation & Why Does it Matter?

Wind has been driving human exploration and industry for millennia. From early wind driven sailing vessels and windmills used to grind grain and pump water to the surface, humanity’s innovations in harnessing the power of the wind have helped propel our civilization. More recently, wind energy has taken on a prominent role in powering our lives in a renewable manner. Wind energy is growing rapidly with offshore wind in particular offering large potential benefits due to its frequent and high-speed winds. Researchers have concluded that there are sufficient wind resources worldwide to meet all current energy demands, although there remain practical and political barriers to achieving this. While Asia and Europe are the current leading markets, the US has ample opportunities for new projects to be developed.

To harness this increasingly important resource, it is vital to understand the seabed and its subsurface. Marine sediments have complex depositional histories with consequently complex and varied structures and soils. Each element of an area’s geological history influences the seabed stratigraphy and presents unique structural features. In addition, the continuous impact of winds and currents create dynamic conditions that are more challenging than those seen onshore, with waves and storms pounding structures at the surface and seabed mobility altering the seabed over time. This affects everything from turbines and power cables to all of the supporting infrastructure and installation equipment needed alongside it, each in different ways, but which all have to be accounted for in the short and long term.

Considering that the largest installed turbine rises over 250m (820 ft.) tall from the water’s surface and weighs in at over 540 tons, it is easy to understand that there are extreme forces placed on the seabed. Wind turbines are only projected to increase in size in the future. At the same time, power cables connecting the turbines to the mainland can stretch for many miles where they will cross many features of the seabed. Without a proper investigation into the seabed’s ability to support these massive loads and extended cables, a project could experience sudden preventable failures that could be catastrophic.

To reduce this risk and the overall costs for a project, surveyors and developers perform detailed geotechnical and geophysical (G&G) site investigations of the seabed, the marine habitats in areas of interest and potential effect, and the subsurface conditions. Together, these inform the design and construction of an offshore wind farm, improving their safety and reducing the chances that an unexpected failure will occur.

Typically, a survey will start with a geophysical campaign. This may entail performing seabed imaging and mapping using tools such as multibeam echo sounders and side scan sonars to identify underwater obstacles and morphologic features - often through repeated surveys to see how the seabed changes over time. Seismic surveys are conducted to characterize the subsurface, visualize its layers and determine where geological structures are present such as buried channels or faults. Unexploded ordnance surveys use marine magnetometers to search for hazards of concern left behind by previous human activities.

Once the seabed has been mapped and sites are selected, a geotechnical investigation is performed that can provide direct information on the mechanical properties of soil and rock. This can be accomplished by directly testing the subsurface using tools such as cone penetrometers, or by extracting samples using equipment such as gravity corers, vibracores, or drill rigs that can provide samples for sophisticated laboratory testing programs capable of determining vital geo-mechanical properties. For benthic surveys, shallow grab samples may provide the necessary information of a seabed’s organisms and habitats. These types of data help ground truth and constrain the geological interpretations performed on the geophysical data. They may also provide valuable archeological information.

Integrating the data acquired during a G&G survey to create 2D and 3D ground models can provide a broad overview of a site’s geospatial variability and hazards while providing detailed information where it is needed most. While a survey can seem expensive upfront, history has shown that a properly executed and thorough survey can reduce the cost of a project by allowing the developer to foresee challenges and prepare solutions before they occur, avoiding costly delays and financial overruns.

With Alpine Ocean Seismic Survey’s history of performing G&G surveys in support of projects across all industries, we wanted to give a brief glimpse of what these investigations may look like in practice and why they are so important. From geotechnical to geophysical, we are proud to be able to assist in providing the high quality and specialized data the offshore industry requires.

While the offshore wind industry in the US is undergoing challenges in 2025, we foresee future opportunities for growth in the coming years here and abroad.

If you should see a research vessel working in your area, they may well be laying the groundwork for the construction of a new wind farm and contributing to the growing global renewable energy market and taking the next step in wind’s contribution to humanity’s progress.