Assessment on earthquake-induced liquefaction around a hybrid monopile foundation for offshore wind turbines with a transition layer model

Offshore wind turbines are currently being developed to have a large size. A hybrid monopile foundation, which is composed of a single pile and a wheel, is advantageous in terms of bearing capacity and liquefaction resistance in liquefiable soil. In this study, the seismic response of a hybrid monopile foundation was investigated using a verified numerical model. Earthquake-induced liquefaction around the foundation was assessed by considering the influence of the foundation dimensions. In the numerical model, a pile-soil contact element was proposed using a transition layer model that effectively buffered the pile-soil interactions. The soil characteristics were evaluated based on the distribution of excess pore water pressure. The liquefaction resistance of the shallow layer was improved by the wheel, and the pile length had a negligible influence on the seismic response. Larger wheel diameter and thickness demonstrated a more pronounced improvement in the anti-liquefaction ability. The influencing zone was determined based on the liquefiable area and had a conical shape under the wheel. This study quantitatively investigated the liquefaction characteristics of a hybrid monopile foundation and provided insights into the numerical calculation of dynamic pile-soil interactions.