Wind Turbine Foundations

Onshore wind turbines are typically installed in rural or remote locations with optimal wind conditions. The foundation must be designed to support a tall, slender structure while withstanding cyclic loading over time.

Geotechnical surveys are vital to assess soil characteristics, groundwater levels, and load-bearing capacities. Foundations for onshore turbines are generally constructed on flat or moderately sloped terrain and must be transportable and installable with minimal environmental disruption.

There are several common foundation types for onshore wind turbines, chosen based on site-specific conditions:

1. Gravity-Based Foundations – This is the most widely used onshore foundation type. It involves a large concrete wind turbine foundation that relies on its own weight to resist the loads. The soil bearing capacity must be sufficient to support the heavy concrete slab, which can be 15–20 metres in diameter.
2. Pile Foundations – Pile foundations are ideal where ground conditions are weak or where the topsoil has poor load-bearing capacity. Steel or concrete piles are driven or bored deep into the ground to transfer loads to more competent soil layers.
3. Rock Anchored Foundations – In rocky terrains, foundations may use rock anchors to secure the base of the turbine directly into bedrock. This reduces the need for large concrete volumes and is suitable for hilly or mountainous locations.

Several foundation types are used for offshore wind farms, depending on water depth, seabed conditions, and turbine specifications:

1. Monopile Foundations – Most common for shallow to medium water depths (up to 30 metres), monopiles consist of large steel tubes driven into the seabed. They provide a simple, cost-effective solution and are quick to install. Aarsleff offers experience in pile driving techniques suited for marine environments.
2. Jacket Foundations – These lattice-style, multi-legged steel structures are suitable for deeper waters (up to 50 metres or more). They offer high stability and reduced weight compared to monopiles, especially in uneven seabeds.
3. Gravity Base Structures (GBS) – Made from reinforced concrete, GBS rest on the seabed and are ballasted to provide stability. Suitable for shallow waters with solid seabeds, they require seabed preparation and substantial transportation logistics.
4. Floating Foundations – For very deep waters where traditional foundations are unfeasible, floating foundations tether turbines to the seabed with mooring lines and anchors. While still emerging, this technology is advancing rapidly and presents new opportunities for offshore wind development.

The construction of wind turbine foundations follows a systematic process to ensure quality and reliability:

1. Site Investigation – Comprehensive geotechnical and hydrological surveys are conducted to assess ground or seabed conditions.
2. Design Engineering – Based on the site data, foundation designs are created and validated to handle all load conditions and environmental factors.
3. Ground Preparation – The construction area is cleared, levelled, and, if needed, dewatered or stabilised for foundation installation.
4. Foundation Installation – For onshore projects, this may involve excavation, rebar placement, and concrete pouring for gravity bases or pile driving for deep foundations. Offshore installations require marine piling vessels, cranes, and specialist divers or remotely operated equipment.
5. Quality Assurance – All construction phases are rigorously monitored for compliance with engineering specifications, tolerances, and environmental requirements.