Case Study: The Use of Post Tensioned Piles for Wind Turbine Foundations-PPT Presentation

PPT Presentation

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The case study describes post-tensioned pile-cap (PTPC) foundations for 63 wind turbines at a Texas wind farm. The 3.15–3.4 MW turbines, with 125 m rotors and 87.5 m towers, imposed high overturning loads and demanding serviceability requirements. Subsurface conditions varied among clay, weaker and denser sands, and mixed soils; stronger layers were sometimes encountered at 50–55 ft.<br /><br />Each PTPC consisted of a 33-ft-diameter, 6-ft-thick cap supported by 24 soil anchors, each 18 in. in diameter. The anchors were designed for a 299-kip allowable tension load and locked off at 398 kips. Four pile lengths, approximately 41–53 ft, were selected to account for soil conditions and the potential for pile refusal in stronger layers.<br /><br />Thirty-five APGD and continuous-flight-auger (CFA) piles were load-tested, with and without post grouting, using PTI soil-anchor procedures. Tests assessed creep, apparent free length, and performance under increasing tension. Non-post-grouted piles generally showed inadequate capacity, failed criteria, or excessive movement. Post grouting substantially increased the capacity of both pile types; post-grouted APGD piles performed slightly better in tension than post-grouted CFA piles.<br /><br />Despite that performance advantage, APGD installation caused significant grout communication and increased pore-water pressure, slowing production and adding uncertainty. CFA piles with post grouting were therefore selected as the preferred solution because they reduced grout communication, improved installation productivity, and provided more consistent, quantifiable installation criteria. Overall, the project demonstrated that post grouting can make pile foundations suitable for the high tension demands of wind turbine foundations, while construction practicality is also essential to selecting the final system.

Keywords

post-tensioned pile-cap

wind turbine foundations

Texas wind farm

post grouting

soil anchors

APGD piles

CFA piles

overturning loads

load testing

pile capacity