Numerical Simulation of Offshore Monopiles with Reinforcement in Shallow Soil Layer

With the development of large-scale offshore wind turbines (OWTs), monopile foundations require larger diameter and greater embedded depth to satisfy the higher bearing requirements. Large-diameter monopiles for OWTs are mainly loaded horizontally, and the horizontal resistance provided by the shallow soil plays an important role in the loading of the monopile foundation. Therefore, shallow soil reinforcement (such as cement grouting and bio-grouting) is an effective method to improve the bearing capacity of the monopile. In this study, the lateral static loading mechanism of a shallow-layer reinforced monopile was investigated by finite element method (FEM). The effect of reinforcements with different stiffness values (elastic modulus), different strengths (cohesion and friction angle) and different reinforced ranges (width and depth) was analyzed on the lateral bearing capacity, deformations, soil resistances, and soil resistance per unit length to pile deflection ( p-y ) curves of monopiles. Based on the numerical results, an empirical formula was proposed for predicting the reinforcement coefficient of the bearing capacity. The effects of different reinforcement parameters on the distribution of soil resistance were analyzed, and the soil resistances obtained by FEM were compared with those from a theoretical formula. It was found that the resistance provided by the reinforced soil was clearly reduced at the interface with the unreinforced soil, and the resistance of the unreinforced soil was not significantly affected by the reinforced soil.