Abstract

During construction of four 2.05 MW wind turbines at Carsington Pasture the ground conditions revealed a complex and highly variable geology much worse than had been anticipated. Preliminary investigations and ground assessment carried out at the conceptual planning stage for the development by other parties had identified the nature and discussed the likely extent of the complexities. These preliminary findings had concluded that the site was located in an area of known karst weathering, with extensive ancient mine workings for lead, and abandoned silica sand pits. The preliminary studies and investigations had confirmed shallow head deposits overlying dolomitic bedrock with a variably pinnacoidal interface, and presence of occasional large pocket deposits consisting of unconsolidated sediments. These finding concluded by optimizing the siting locations for each structure. During development, the ground conditions revealed at each location differed significantly and it was realized early on that no single ground remedial solution would be possible to adequately reinforce and suitably improve the bedrock foundation base for the envisaged design life. The challenging ground conditions necessitated extensive non-intrusive ground investigation followed by shallow and deep intrusive investigation to better define the ground conditions. The paper describes the unexpected and unusual combination of ground conditions that were encountered and their implications for foundation development, and examines the development of the bespoke engineered ground solutions developed for each of the four turbines. The experience at Carsington Pasture provided direction for the successful development of a further two wind turbines in an adjacent site located at Ryder Point situated over equally complex ground conditions. The paper concludes with discussion of how the experience of the combination of difficult ground conditions encountered at Carsington Pasture and their management served to guide the investigation, foundation development and successful construction of wind turbines in the adjacent area, and demonstrates the wider value of project examples and experience afforded by case studies.

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