The gravity-base (or inverted-T) foundation is the most common system for supporting onshore wind turbine towers. Gravity base foundations, or gravity foundations, are a proven choice for onshore wind turbines. Their name is derived from the fact these foundations rely on gravity for their stability. This shallow foundation typically extends 7 to 12 feet below the surface and relies on gravity to provide stability against overturning forces, hence its name. Over the past twenty years, the wind energy industry has experimented with various foundation shapes including various versions of the octagonal shape to settle on a circular design. Circular foundations have become the standard since the mid-2010s. This preference is due to the advantages they offer, reduced concrete and steel usage, improved constructability, and overall higher efficiency.

In this video, we outline the key steps involved in constructing a gravity-base foundation. Please note that the sequence presented is for educational purposes and may differ from the actual construction process, which can vary depending on site-specific needs.

• Base Slab: The bottom-most layer, often made of reinforced concrete, provides a large, stable base that rests on the ground. This slab spreads the load from the turbine and ensures that the pressure exerted on the soil remains within acceptable limits.

• Embedment Ring Placement: The embedment ring is a steel ring embedded in the concrete foundation, serving as the anchor point for the wind turbine tower. It is carefully positioned and leveled on the base slab using spacers to ensure precise alignment with the anchor bolts. The ring interacts with the bottom mat of rebar and keeps the anchor bolts aligned within PVC sleeves, allowing them to be tensioned after tower installation.

• Bottom Mat of Rebar: The bottom mat of rebar is placed on top of the embedment ring and extends into the anchor bolt cage. The rebar is supported by small concrete blocks called “dobies” to ensure the rebar gets fully covered by the concrete.

• Anchor Bolts Installation: The anchor bolts are positioned inside PVC sleeves that run through the base slab. These bolts are only attached at the bottom to the embedment ring and remain loose from the concrete, allowing them to be stretched out (tensioned) from the top. The template ring is placed on top to keep all the anchor bolts in line. It acts as a space holder during the main concrete pour. After the pouring, it is removed to allow for the grout layer, which will be poured in when the first tower section is placed and leveled.

• Top Mat of Rebar: The top mat of rebar, which includes bars for the conical section and the pedestal part in the center, is installed. These bars also extend through the anchor bolt cage.

• Concrete Pour: The main concrete pour is conducted, encasing the rebar and forming the bulk of the foundation.

• Soil Backfill: After the concrete has been set, dirt backfill is applied around the foundation to provide additional stability and protection.

• Pedestal: This is the central part of the foundation that connects the wind turbine tower to the base slab. The pedestal is usually cylindrical or conical and serves as the transition point where the loads from the turbine are transferred down to the base slab.

Civil renewable Inc. efforts were instrumental in establishing circular foundations in the United States as the industry standard. More details on these contributions can be found on our website at www.civilrenewables.com. Today, we continue to innovate, developing new foundation systems that further enhance efficiency by minimizing resource use and improving constructability. We look forward to sharing more about these innovative solutions, which we believe will further advance the industry toward greater efficiency and accessibility.

At Civil Renewables, we view wind turbine foundations as essential for more than just structural support—they play a key role in long-term stability, performance, and environmental care. While the gravity base foundation design is widely adopted, we are actively working on innovations that will improve its reliability, longevity and resource efficiency. Stay tuned for exciting advancements in foundation technology!