Study on cumulative displacement and secant stiffness of monopiles in sandy soil under the effect of cyclic lateral loads

Monopiles are the most used offshore wind turbine foundation. They are also used in oil docks and dolphin piers. Monopiles are usually 2 to 8 meters in diameter. In these piles, the ratio of free length to diameter is about 5 to 15 and the ratio of driven length to diameter is about 2 to 6. The basic concepts for monopiles in deep water are still unclear. Thus current methods lead to non-economic designs. The main purpose of this study is to investigate the mechanical behavior of a monopile under the influence of cyclic lateral loads in sandy soils. In this research, 9 Tests were designed and implemented to geotechnical centrifuge modeling at 40g acceleration. The model pile is a 5.1cm in diameter steel pipe installed in Firouzkouh-161 sand and the cumulative displacement and secant stiffness of the system were investigated by cyclic lateral loading. Based on the results of the modeling, formulas have been proposed to estimate the displacement and stiffness of these piles under the effect of different cyclic lateral loads. The results of this research show that the most important factors in the cumulative deformation of the monopile head are the type and cyclic load amplitude.