Abstract
Foundations for offshore wind turbines (OWTs) are mainly open-ended piles that are subjected to cyclic loadings caused by winds, waves and currents. This study aims to investigate the dynamic responses of open-ended pipe pile under lateral cyclic loadings, as well as the characteristics of the soil plug and surrounding soil. Both large-scale indoor model test and discrete element simulation were adopted in this study. The test results show that the resistance of each part of the pipe pile increases linearly with depth during the process of pile driving. The pile side resistance degradation effect was also observed along with the friction fatigue. The soil plug formation rate decreases gradually with an increase in the pile depth. The influence range in the surrounding soil is about 5~6 times of the pile diameter. The cumulative displacement of the pile head increases with the number of cycles. Lateral tangential stiffness and lateral ultimate bearing capacity decreases with an increase in number of cycles. The severe disturbance range of soil around the pile is 2~3 times of the pile diameter. The center of rotation of the pile body is about 0.8 times of the pile body depth. The side frictional resistance and lateral pressure of the pile body is found to fluctuate along the pile body. Additionally, the lateral pressure and side friction resistance decreases gradually with decreasing tendency of the former more than the latter.
Highlights
The open-ended pile is a common option of foundations for offshore wind turbines (OWTs)
The deformation characteristics of pile foundations under cyclic loadings are important for the safety of OWTs
Matlock [1] proposed the p-y curve calculation method, which was adopted by the US American Petroleum Institute (API)
Summary
The open-ended pile is a common option of foundations for offshore wind turbines (OWTs). Large amounts of research concerning the large-scale pile group have been conducted These studies include the extensive experimental tests subjected to cyclic lateral loading [19,20,21,22], which reveals the highly nonlinear nature of the pile-soil-pile interaction, and the analysis method for laterally loaded pile groups, that takes into account the non-linear behavior of the soil and the non-linear response of reinforced concrete pile sections simultaneously by the newly proposed Boundary Element Method (BEM) approach [23]. Understanding the micro-mechanisms is essential to interpret the macro-behavior in complex geotechnical issues [27] In this paper, both the numerical simulation and model test were used to the reveal the comprehensive responses of the soil-pile system during the long-term lateral loading, including the micro-mechanisms and macro-behaviors both inside and outside the pile. A double-walled pile system was applied in both the tests and numerical simulation to separate the internal and external frictions
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