Addressing ground constraints for onshore wind projects

While grid connection and planning considerations often take early focus for onshore wind projects, the physical and geological characteristics of a site ultimately govern how, and in some cases whether, a project can be built. The physical and geological characteristics of a site influence not only how turbine foundations are designed, but also the constructability of access tracks, crane hardstands, substations, cable routes, and other supporting infrastructure. If difficult or variable ground conditions are identified too late, they can drive redesign, programme delays, construction complexity, and increased cost.

At the centre of this ground constraints challenge is the installation of turbine foundations. Over a design life of 30 years or more, these structures must reliably transfer the blades’ significant static and dynamic loads into the ground while making sure the turbine continues to perform within specification throughout a wide range of operating loads and environmental conditions.

In order for foundations to ensure the turbine’s long-term performance, the strength and stiffness of the site’s ground needs to be fully characterised. Subsurface conditions are rarely uniform and variations in soil type, rock quality, layering, and groundwater levels all influence how loads are distributed and how the ground will behave over time, influencing foundation stability. This is particularly relevant because many wind developments extend over large areas and ground conditions may vary significantly between individual turbine locations.

Without an adequate understanding of the subsurface environment, developers face increased uncertainty around project design, programme, cost, and constructability, meaning ground and geological site conditions should be treated as a project delivery risk which needs to be adequately defined early, before it becomes a critical path constraint for onshore wind development.

Steps to mitigate ground condition risk

Addressing ground-related risk for onshore wind projects is rarely about a single intervention; it’s about combining several practical steps to reduce uncertainty and support a robust and buildable design. Typically, this starts with getting a much clearer understanding of the ground conditions early on, through detailed desk studies followed by a design-led ground investigation strategy tailored to the project’s requirements. Depending on the site conditions, this may include boreholes, trial pits, in-situ testing and, where appropriate, geophysical surveys to characterise the ground and determine the engineering parameters required for design. Where peat is present or anticipated, additional investigations such as peat depth probing and peat landslide hazard and risk assessments may also be required. Groundwater monitoring is also important, as high groundwater levels and poor drainage can affect soil strength, excavation stability, earthworks performance, foundation behaviour, and construction requirements.

Once there’s a better understanding of what’s below ground, design decisions can respond accordingly. Turbine locations, for example, don’t have to be fixed from the outset – small adjustments in position (known as micro-siting) can help avoid the worst ground conditions, whether that’s deeper zones of weaker soils or areas of instability. These changes can make a noticeable difference, often simplifying foundation design and reducing the amount of earthworks required without materially affecting energy yield.

Early geotechnical information can also support optimisation of the foundation solution itself. A better understanding of ground conditions and their variability can help avoid unnecessarily conservative designs and identify where simpler foundation solutions may be appropriate, potentially reducing excavation, concrete volumes, ground improvement, or the need for more complex foundation systems.

However, ground conditions are inherently variable, and no amount of investigation removes that entirely. Projects that run the most smoothly are those that accept this, accurately defining foundation types but also building in some flexibility – whether that’s allowing room for small layout changes or carrying contingency in programme and cost. Taking a structured, risk-based approach means that when issues do arise, they can be managed without derailing the entire project.

How SLR can help

Ultimately, ground conditions influence timelines in two key ways: by introducing uncertainty that requires time to resolve, and by affecting the speed and complexity of construction activities. Projects that fail to recognise this early often experience delays, while those that invest in understanding and designing around the ground from the outset are far better placed to maintain programme certainty.

SLR’s Geotechnical Engineering teams have extensive experience in evaluating ground conditions and supporting the design of onshore wind turbine foundations to suit the ground conditions of the site. Get in touch with our teams to learn how we can support your project.