Effects of Helical Anchor Geometry on Long-Term Performance of Small Wind Tower Foundations Subject to Dynamic Loads-Article

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The study evaluated how the number of helical plates affects long-term performance of anchors used for guyed small wind towers. Researchers instrumented a 10-kW wind tower to measure cable loads and vibrations, then reproduced representative operating and extreme wind loads in field tests of five anchors with two, three, or four helices. The anchors were tested under repeated dynamic tension for two to four weeks, with site soil and water-table conditions monitored.<br /><br />All anchors showed some initial movement under seating loads, likely related to installation disturbance or shaft alignment. After seating, performance differed by geometry. The tested two-helix anchor developed substantial, ongoing creep—even under loads within a factor of safety of two. The authors suggest it may have penetrated a weak soil layer or had insufficient bearing area, though the limited number of tests prevents a firm explanation. Three- and four-helix anchors generally showed little additional movement under working and extreme loads. The three-helix anchors performed well, while the four-helix anchors offered no clear performance advantage sufficient to justify their additional material in this study.<br /><br />The authors therefore identify the three-helix configuration as the most economical option for dynamically loaded wind-tower guy anchors, provided it is installed to the required torque and in suitable soil. They caution that installation torque alone does not guarantee resistance to future creep: soil layers, water-table changes, and anchor placement also matter. They recommend considering a preloading cycle to seat anchors before attaching guy cables, while noting that unusually large seating movement may signal a poor or inclined installation. Because the results come from a small, site-specific field program, additional testing is needed to confirm the effects of helix number and size.

Keywords

helical plates

wind tower anchors

guyed small wind towers

dynamic tension

anchor creep

soil conditions

water table

three-helix anchor

four-helix anchor

installation torque