Geotechnical Design Challenges for Solar Farm Tracker Piles in Reactive Clays-Paper

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The paper examines geotechnical risks to solar-tracker piles installed in Australia’s reactive clays, where seasonal soil-moisture changes can cause ground heave, shrinkage and loss of lateral support. Although solar farms often use shallow piles to reduce costs, their long-term performance is uncertain and has received limited field-scale research.<br /><br />A central design concern is the depth of seasonal moisture change, commonly estimated using the Thornthwaite Moisture Index (TMI). TMI-based estimates rely on long-term averages and broad climate maps, which may overlook local conditions, extreme wet–dry events and future climate shifts. A case study shows that estimated suction depths can vary substantially between weather stations and over time; the authors argue that designers should assess the probability of exceeding average design conditions rather than relying on averages alone.<br /><br />The paper also highlights desiccation cracking, Gilgai ground undulations and soil jacking. Cracks may reduce soil support around piles, while wetting can produce uplift; repeated cycles may progressively lift shallow piles. Livestock grazing and vegetation changes can influence cracking and soil moisture. These effects are difficult to predict because long-term field data remain scarce.<br /><br />Existing analytical methods offer useful preliminary tools for estimating pile uplift, axial forces and lateral response, but their assumptions and limitations require caution. Cracks at the pile–soil interface can increase lateral displacement and bending moments, potentially raising structural and buckling risks.<br /><br />The authors recommend thorough site investigation, attention to local climate and ground variability, monitoring and use of local expertise. Designs should explicitly assess climatic extremes, cracking and long-term movement, and communicate residual risks to asset owners. Cost savings from shallow embedment should be weighed against whole-of-life performance; where risks cannot be reliably quantified or mitigated, conservative, robust designs are warranted. Further research and high-quality field data are needed to improve predictive methods.

Keywords

solar tracker piles

geotechnical risk

reactive clays

seasonal soil moisture

ground heave

Thornthwaite Moisture Index

desiccation cracking

pile uplift

lateral support

field-scale research