The Inner Workings of Gravity Base Foundations
We’re thrilled to share our latest video, which offers more detailed information on gravity base foundations—a proven wind turbine foundation system.
Built from reinforced concrete, gravity base foundations are specifically designed to withstand the powerful forces exerted by wind turbines. In this video, we guide you through the arrangement of the rebar that fortifies the structure, and we break down the steps involved in the construction process. Over the years, this system has undergone continuous refinements to improve its reliability and resource-efficiency (see our blog on shape optimization of gravity-base foundations). Nowadays, the gravity base foundation has become an established solution for providing durable support for towering turbines while minimizing material usage.
Explore this video to discover the unseen foundation that drives the future of wind energy and supports our renewable energy ambitions.
Gravity based foundations, commonly used for onshore wind turbines, are shallow systems that rely on their mass and the weight of the backfill for stability. Extending only 7 to 12 feet below ground, they are a proven foundation system that is suitable for various soil conditions. Let's take a closer look at the main components and construction sequence of a standard gravity-based foundation:
The first concrete layer, known as the mud mat or blinding, is made of lean, unreinforced concrete and serves as a clean working surface for the foundation construction activities. This layer is placed only after the foundation subgrade has been approved for conformity with the assumed geotechnical design conditions.
Next, the anchor bolt cage is either brought in pre-assembled or assembled on-site and then set and leveled on rigid supports. The anchor bolt cage consists of sleeved steel rods spanning between a steel embedment ring towards the bottom of the foundation slab and a template ring at the top of the foundation.
Once the anchor bolt cage is set and leveled at the exact spot of the wind turbine, foundation reinforcement is added starting with the bottom mat and continuing with vertical pedestal bars, support chairs, shear reinforcement and then top mat reinforcement. The bottom mat bars are typically supported on small concrete blocks known as dobies, ensuring the rebar is fully encased in concrete.
The vertical slab edges are then formed, and the main slab concrete pour follows, encasing the rebar and forming the bulk of the foundation.
Once the slab concrete sets, the remaining pedestal reinforcement is added, and the pedestal is then formed and poured.
Once the foundation concrete gains sufficient strength, soil backfill is placed and compacted in layers on top of the foundation slab for additional stability and protection.
Summary
In the above video, we dive into more details on how these critical foundations, made of reinforced concrete, are engineered to handle the immense forces generated by wind turbines. From the intricate rebar layout to the step-by-step construction process, you'll see how this system is optimized for constructability and reliability. These elements are expertly engineered to support wind turbine foundations that surpass industry standards for stability, efficiency, and durability. At civil renewables, these principles drive every foundation design with a strong focus on making them more affordable, sustainable and resource efficient.
