Failure Envelopes of Single-Plate Rigid Helical Anchors for Floating Offshore Wind Turbine.

Helical anchor is a kind of novel foundation for floating offshore wind turbines, which should be subjected to combined tensile loading caused by wind, wave and current. However, the research about the capacity of helical anchor was mainly examined under uniaxial loading and scarcely explored under combined loading. In this study, three-dimensional finite element limit analysis is adopted to assess the bearing capacities of single-plate rigid helical anchors with different ratios of helix to shaft diameter, D_H/D_S and embedment ratios L/D_S. Result shows that the vertical, horizontal and moment bearing capacities increase with increasing D_H/D_S and L/D_S. The normalized V-H failure envelopes expands with increasing L/D_S, while the normalized V–M failure envelopes tend to contract with the increase of D_H/D_S. With increasing D_H/D_S or decreasing L/D_S, the normalized H-M failure envelopes expand when the horizontal and moment loading act in the same direction and contract when they act in the opposite direction. The effect of D_H/D_S and L/D_S on the shape of H–M failure envelope become insignificant when L/D_S ≽ 4. A series of failure mechanisms under different loading conditions were observed and can be used to explain the trend. Besides, a series of approximate expressions were proposed to fit the uniaxial bearing capacities and the failure envelopes. [ABSTRACT FROM AUTHOR]