Numerical Investigation of Mechanisms Affecting Performance of Cyclically Loaded Tension Piles in Sand

Offshore wind turbines supported on jacket structures are subject to many cycles of axial loading due to wind and waves, which may densify the soil around the piles and decrease the lateral stress on the soil-pile interface. Static axial loads may cause dilation of adjacent soil and increase the lateral stress. Results from model tests have demonstrated the potential for increases and decreases in pile stiffness, capacity, and pullout rate depending on the combination of static and cyclic loads, but the fundamental mechanisms are not fully understood; a one-dimensional, axisymmetric finite-element model is developed to investigate these mechanisms. The Dafalias-Manzari bounding surface plasticity model is used for the soil. Downward shear and cavity expansion at the pile interface are used to simulate installation, which is followed by the application of static tension and cyclic loads. Static tension causes initial contraction of near-pile soil, followed by dilation if the tensile load is further increased. Presence of a moderate static tension results in increased stiffness initially in one-way cyclic loading. With additional cycling, overall contraction in the far field leads to reduction of lateral stress and localized dilation (loosening) at the interface. Furthermore, if the cyclic loads cause small plastic deformations, however small, the numerical model suggests that tension piles would eventually pull out. Limitations of the numerical model are critically assessed.

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  • English

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  • Accession Number: 01717629
  • Record Type: Publication
  • Files: TRIS, ASCE
  • Created Date: Aug 5 2019 3:02PM