Soil deformation under cyclic horizontal load in sand: Insights from experiments

In addition to making a significant contribution to the reduction of carbon emissions, the offshore wind industry has played a significant role in the production of green energy. However, the foundation of offshore wind turbines is threatened by extreme wave loads in the long-term during normal service. Such loads alter the strength and stiffness of surrounding sand affecting the ultimate capacity and serviceability of the pile foundation. To explore the interaction mechanism between pile and soil, this study combines a model test system with Particle Image Velocimetry (PIV) to study the deformation and stiffness degradation characteristics of the soil around piles under wave loading. The results indicated that the behaviors of the horizontal displacement at the pile top remain consistent regardless of the different triggers, and their general performance can be divided into three stages: linear, sluggish-growth, and stable-deformed stage. Furthermore, the deformation fields of passive zone soil mass exhibit a wedge-shaped distribution, while active zone soil shows significant differences under different loading conditions. In this study, the stiffness degradation model of the soil around the pile was optimized, and the calculated results are in good agreement with the experimental results. The model can be used to evaluate the stiffness degradation of soil under wave loading, and the research results can provide references for designing monopile foundations for offshore wind turbines.