Throughout their lifespan, monopile foundations supporting offshore wind turbines inevitably experience horizontal loads from waves, winds, and currents, resulting in cumulative deformation. It has been believed that deformation caused by horizontal loading weakens the interaction between the pile and the soil, leading to a reduction in the ultimate uplift bearing capacity of the pile foundation. However, there is a scarcity of literature investigating this issue, particularly regarding monopiles used in offshore wind turbine installations. Therefore, this study aims to explore the impact of horizontal cyclic loads on the ultimate uplift bearing capacity of monopile, focusing on the pile–soil interaction. To achieve this, a series of 1 g model tests were conducted on a rigid model pile embedded in silt with varying relative compaction. The test results indicate that the ultimate uplift bearing capacity of the pile is significantly diminished after experiencing horizontal cyclic loading, and the extent of reduction is closely linked to the amplitude of the horizontal deformation. A semi-empirical model is developed to predict the ultimate uplift bearing capacity of the pile foundation following horizontal cyclic loading. The key findings of this study are as follows: (1) The earth pressure in the active zone gradually decreases with an increasing number of cycles, while the earth pressure in the passive zone experiences a slight increase under horizontal cyclic loading. (2) The position of the pile rotation center under horizontal cyclic loading is approximately 0.84 times the depth at which the pile is buried, and this relationship appears to be independent of soil density and cyclic load ratio. (3) The variation of earth pressure corresponding to the horizontal deformation of the pile in the active zone can be divided into three phases: a rapid decline phase, a slow decline phase, and a stable phase. (4) The reduction in the ultimate uplift capacity is influenced by the cyclic ratio and number of cycles but does not appear to have a significant relationship with soil density.

Pile foundations are commonly used to support structures subjected to complex loading conditions. In seismic-prone regions, understanding the soil–pile interaction under cyclic loading is essential for ensuring the stability and safety of these foundations. Numerical modeling is an effective tool for predicting the nonlinear behavior of soil under seismic excitation, but selecting an appropriate constitutive model remains a significant challenge. This study investigates the seismic behavior of pile groups embedded in soft clay using advanced finite element analysis. The piles are modeled as aluminum with a linear elastic response and are analyzed within a soil domain characterized by two kinematic hardening constitutive models based on the Von Mises failure criterion. Model parameters are calibrated using a combination of experimental and numerical data. The study also examines the influence of pile spacing within the group on seismic response, revealing notable differences in the response patterns. The results show that the nonlinear kinematic hardening model provides a more accurate correlation with experimental centrifuge test results compared to the multilinear model. These findings contribute to enhancing the understanding of soil–pile interaction under seismic loading and improving the design of pile foundations.