The elastoplastic model can more accurately simulate the elastoplastic behavior of soil in the process of loading, so as to determine the soil resistance more accurately, which holds great significance in calculating the bearing capacity of pile foundations. However, the current study has not found that the elasticity of soil is taken into account to analyze the dynamic behavior of pile foundations. To study the dynamic response of pile foundation under horizontal cyclic load, theoretical calculation methods and model tests are applied. Based on the flexural differential equation of pile and considering the inertia force of the pile under harmonic load, the analytical solutions for the displacement and bending moment of pile foundation under horizontal cyclic load are obtained. The accuracy of the calculation method is confirmed through comparison with experimental results. An analysis is conducted to examine the impacts of harmonic load amplitude and frequency, foundation reaction coefficient, and pile bending stiffness on the plastic height. The changing rules of the pile bending moment and pile displacement with harmonic load amplitude, foundation reaction coefficient, and pile bending stiffness are studied. By comparing the theoretical and experimental results with numerical methods, it is found that the general trend of the experimental and theoretical results is consistent. It is found that as the harmonic load frequency increases, the foundation reaction coefficient decreases, and the harmonic load amplitude increases, there is a corresponding augmentation in the plastic height of the soil, pile displacement, and bending moment.

Pile-anchor foundations, serving as one of the anchoring solutions to ensure the safety and stability of floating offshore wind turbines, are primarily subjected to inclined loading induced by anchor chain forces, resulting in significantly different bearing behavior compared to conventional vertically loaded pile foundations. However, experimental research on the inclined pullout performance of anchor piles remains insufficient. To address this gap, this study employs a self-developed servo-controlled loading system to investigate the pullout bearing characteristics of anchor piles in dry and saturated sand, considering factors such as pullout angle and loading point depth. The research results show that from the load–displacement curve of the model pile, it can be found that with the increase in displacement, the load it bears first gradually increases to the peak, then decreases, and then gradually stabilizes. The loading angle has a significant impact on the bearing performance of pile-anchor foundations. As the loading angle increases, the failure mode shows pullout failure. When the loading angle increases from 30° to 60°, the bearing performance of the pile foundation decreases by approximately 63%. When the depth of the loading point increases from 0.22 times the pile length to 0.78 times the pile length, the diagonal anchor tensile bearing capacity of the model pile increases by approximately 45%. When the depth of the loading point is the same, the distribution patterns of bending moment and shear force are basically similar. However, the smaller the loading angle, the larger the value. This is because the horizontal load component plays a dominant role. The compression of the piles above and below the loading point, as well as the bending moment, shear force and axial force under saturated sand conditions, are similar to those in dry sand, but their values are reduced by about 50%. It can be seen that the soil conditions have an influence on the bearing characteristics of pile foundations.

Concrete-filled FRP (Fiber Reinforced Polymer) tube composite piles offer superior corrosion resistance, making them a promising alternative to traditional piles in marine environments. However, their performance under cyclic lateral loads, such as those induced by waves and currents, requires further investigation. This study conducted model tests on 11 FRP composite piles embedded in sand to evaluate their behavior under cyclic lateral loading. Key parameters, including loading frequency, cycle count, loading mode, and embedment depth, were systematically analyzed. The results revealed that cyclic loading induces cumulative plastic deformation in the surrounding soil, leading to a progressive reduction in the lateral stiffness of the pile–soil system and redistribution of lateral loads among piles. Higher loading frequencies enhanced soil densification and temporarily improved bearing capacity, while increased cycle counts caused soil degradation and reduced ultimate capacity—evidenced by an 8.4% decrease (from 1.19 kN to 1.09 kN) after 700 cycles under a 13 s period, with degradation rates spanning 8.4–11.2% across frequencies. Deeper embedment depths significantly decreased the maximum bending moment (by ~50%) and lateral displacement, highlighting their critical role in optimizing performance. These findings directly inform the design of marine structures by optimizing embedment depth and load frequency to mitigate cyclic degradation, ensuring the long-term serviceability of FRP composite piles in corrosive, high-cycle marine environments.