Failure mechanism of single pile-friction footing hybrid foundation under combined V–H–M loadings by PIV experiments and FE method

Abstract

The traditional monopile foundation is confronted with challenges in the context of the new generation of offshore wind turbines with greater power capacities. On this basis, the single pile-friction footing hybrid foundation is investigated, whose bearing capacity is largely improved by combining a circular friction footing at the mudline. This paper discusses the failure mechanisms and bearing capacities of this hybrid foundation in sand under combined vertical-horizontal-moment (V–H-M) loadings by laboratory experiments and the finite element method. By adopting Particle Image Velocimetry (PIV) technology in model tests, failure mechanisms of a single pile and the hybrid system are compared. The results show that the cavitation and compaction phenomenon can be captured in the depth range of 0–0.7 pile embedment depth) for the hybrid foundation. Also, due to the settlement of the footing, a deformation area with a concave area and a small peak value can be found under the footing, which is quite different from that of the pile under V–H-M combined loadings. Intensive parametric studies were performed through FE method, and the results indicate that increasing the footing diameter has a more pronounced effect on the bearing capacity compared to that of increasing the length-diameter ratio of the pile.