Pile Design For Solar Farms And Reactive Clay Sites In Australia

S J Goodall and R S Merifield


There are many geotechnical aspects that require consideration during the design of solar farms. One key consideration, which is a major cost driver for these developments, is the design of the pile foundations supporting the solar arrays. The number of piles is often in the order of tens to hundreds of thousands and contributes to a significant portion of the capital cost of the project. The uptake of commercial scale solar is in its infancy in Australia with the first commercial size farm only commencing operation in late 2012. Consequently, we have limited local case studies for lightly loaded piles installed in reactive clay subjected to wetting and drying cycles on which to base a rational design methodology. Methods are available to analyse this type of problem. However, many are based on simplified assumptions, limited data sets, or can be difficult to apply in practice. Furthermore, some of the available methods rely on laboratory tests, such as swell pressure measurements, of which the results can be highly variable and difficult to rationalise, or insitu tests that are difficult to undertake in engineering practice. This paper provides an overview of the current state of practice in Australia for designing piles supporting solar arrays to resist expansive soil movements and presents some preliminary design charts developed using finite element analysis to assist designers with estimating the vertical pile movements and loads in piles associated with reactive ground movements.