Effect of Anisotropic Behavior of Soft Clay on the Nonlinear Consolidation of Composite Pile‐Improved Soft Ground Considering Size and Rotational Hardening

ABSTRACT Composite piles are a promising technique that improve the stability and loading capacity of soft ground, offering superior performance over traditional methods. Natural soft clays often tend to exhibit pronounced anisotropy, which can substantially affect the consolidation behavior of composite ground. This study presents an analytical consolidation model for composite ground that explicitly incorporates the anisotropic behavior of surrounding soft clay. The model is developed under the equal strain assumption, which is well‐suited for conditions beneath rigid loading platforms such as embankments or raft foundations. The annular equivalent method is employed to accommodate various practical geometries of composite piles. The mechanical behavior of the soft clay is characterized using a yield surface consistent with the S‐CLAY1 model, represented by an inclined ellipse to account for inherent anisotropy. The model integrates both size hardening and rotational hardening laws to describe the evolution of anisotropy under progressive loading. Comparative verification against existing analytical solutions confirms the accuracy of the proposed model. A detailed parametric study is conducted to investigate the influence of key anisotropic parameters, including the critical‐state friction angle , the evolution rate of rotational hardening , and the volumetric‐shear strain weighting factor , on the nonlinear consolidation behavior of the composite ground. Results indicate that higher accelerates consolidation due to increased soil stiffness, while lower values enhance system stiffness and excess pore pressure dissipation. Conversely, increasing reduces the effect of volumetric strain on rotational hardening, leading to greater compressibility and slower consolidation.