27 Victor Proceedings
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Foundations: Proceedings of the Second BGA International Conference on Foundations, ICOF2008. Brown M. J., Bransby M. F., Brennan A. J. and Knappett J. A. (Editors). IHS BRE Press, 2008. EP93, ISBN 978-1-84806-044-9. www.ihsbrepress.com 27 HELICAL ANCHORS AS WIND TOWER GUYED CABLE FOUNDATIONS R. T. VICTOR and A. B. CERATO University of Oklahoma, Civil Engineering and Environmental Science, 202 W. Boyd, Norman, OK 73072, USA [email protected] SUMMARY: The current research is dedicated to developing design parameters and installation charts for the use of helical anchor foundation elements in application with 1 to 10 kW guyed and free standing turbines. The effects that dynamic loading and varying water table conditions have on the pullout capacity of helical anchors are the focus topics of t his research. This study supports better predictions of helical anchors’ capacities without intensive and intrusive soil tests. Field testing was performed on four -helical anchors that were installed vertically to designated torque values to be tested for pullout capacity (tension). Static tests, short- and long-term, were performed on three anchors (one 4-helix and two 2-helix), and dynamic testing was conducted on one anchor (2-helix) in long-term testing followed by a static short-term pullout test. The conclusions obse rved from static and dynamic testing include the effects on an anchor’s static uplift capacity from dynamic loading and influences from varying groundwater conditions, and the validation and further establishment of the torque correlation method. The findings in this paper indicate that cyclic loading influences on static uplift capacity are dependent on installation conditions, and that a rising groundwater table lowers the installation torque predicted uplift capacities. Keywords: cables, cyclic loading, guyed cable foundations, helical anchors, wind turbine foundations. INTRODUCTION The proposed application of this study is to use helical anchors as a foundation system for small wind turbines (1–10 kW) guyed wires (tension applications). Helical anchors are currently used to anchor guyed wires of cell or transmission towers. However, the increased dynamic vibrations that a wind turbine adds to the tower and foundation system under working loads, as well as under extreme conditions (e.g., straight line winds, ice load or sudden furling shocks), require additional knowledge about the behavior of helical anchors under field conditions. These field conditions were simulated in this study by instrumenting a working tower to gather data on wind speed, direction and variability and tower response. These tower responses were then transmitted to the helical anchors in
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