A novel t-z model to predict the pile responses under axial cyclic loadings

Abstract

Jacket foundations are generally used for the offshore wind turbines (OWTs) with water depth more than 30 m. During the service period of OWT, the piles of jacket foundation are mainly subjected to axial cyclic loadings caused by winds and waves. Thus, the axial interaction between the pile and its surrounding soil is the key problem for the design of jacket foundation. In this paper, a novel t-z model was proposed to predict the pile responses under axial cyclic loadings. Model parameters were calibrated through cyclic interface shear tests, and then numerical studies were performed. The results indicate that the cyclic loading modes (two-way, one-way tension and one-way compression) and cyclic load amplitude have obvious effects on the pile axial responses, including accumulated pile displacement, pile axial force, pile-soil interface resistance. It is noted that the displacement of pile accumulates with a fast speed in the one-way cyclic tension mode. With the increase of load amplitude, the maximum residual axial force of pile increases downward significantly except for the shallow depth. The proposed t-z model is appropriate for the assessment of accumulated displacement evolution of jacket foundation at seabed level.