Stability of wind turbine foundations - accounting for gapping and eccentric loading : geotechnical engineering

In the last two decades, the global development model has shifted to idealise sustainable development, as well as to promote 'green' and renewable ideals. South Africa, following the example of other more developed nations, has tackled these ideals by beginning to supplement its energy production infrastructure with more sustainable alternatives and, with the exception of its planned new nuclear scheme, has committed to a reduction in non-renewable production methods over time. This was highlighted in the country's 2012 Integrated Energy Plan, where the National Energy Regulator committed to investing 1 600 MW a year in renewable energy infrastructure, of which half is dedicated to wind energy and the creation of wind farms. With this increase in scope, understanding the complexities of turbine engineering has never been more important for South African engineers. Foundation designs for these structures pose a series of complex challenges, due to the unique loading characteristics that turbines inherently possess, as well as the wide variety of soil conditions that exist within the South African wind energy corridors. One of these challenges is to provide a safe approximation of the bearing capacity, which must account for the extremely large gravity and moment loads that the structure experiences during normal operating conditions. This leads to very large eccentricities, which can often destabilise a footing to the point of failure. This article introduces and discusses the various turbine loads and how they can be theoretically accounted for in the design of a conventional gravity footing for a wind turbine structure.