Research on shear characteristics of pile–soil interface under cyclic loading

Abstract

Offshore wind turbine constructions are developing rapidly in China. Generally, large-diameter rigid steel piles are used in offshore wind turbine foundations. However, existing design methods for pile foundations with bearing capacity are often based on small-diameter flexible piles and are inapplicable to real situations. Simultaneously, thick layers of clay cover the fields. Therefore, the shear characteristics of pile–clay interface require examination to optimize design methods. A large-scale interface shear test model corresponding to laboratory tests is established using PFC software, and the micro-parameter values are validated. The simulation results well follow the laboratory test results, and the model accurately reflects pile–clay interactions during shearing. Based on the simulation model, the shear characteristics of the steel–clay interface under different normal loads, cyclic load frequencies, and cyclic load amplitudes are analyzed. With an increase in normal load, the shear strength of the steel-clay interface increases gradually, whereas it slightly decreases with an increase in the cyclic load frequency and amplitude; particularly, the effect of amplitude is significant. The mechanical response of clay at a mesoscopic scale is analyzed. Results show that the greater the normal load, the greater the horizontal displacement of particles. However, the influence of cyclic load frequency and amplitude is the opposite: normal load does not change the contact force distribution of soil particles, and clay volume change is determined by the normal load. Thus, this study provides support for bearing capacity prediction of offshore wind farm pile foundations.