Analytical Solutions of Nonlinear Consolidation for Composite Pile–Improved Ground with Anisotropic Soft Clay Considering Time- and Depth-Dependent Well Resistance and Stress Dispersion

Composite piles are commonly installed in soft ground to enhance load-bearing capacity. The remarkable anisotropy of natural soft clays can strongly influence the consolidation process of composite pile–improved ground. In addition, time-dependent clogging and depth-dependent well resistance may significantly impair the drainage performance of the gravel shell in composite piles. Based on the equal-strain assumption, this study develops a nonlinear analytical consolidation model for composite pile–improved ground that explicitly incorporates soil anisotropy, time-dependent clogging, depth-dependent well resistance, nonlinear soil behavior, and stress dispersion. To capture the anisotropic behavior of soft clay, a constitutive model with an inclined elliptical yield surface, a size hardening law, and a rotational hardening law is introduced. The analytical solutions under instantaneous loading are derived using the method of separation of variables combined with Bessel functions. Model performance is validated through several existing analytical consolidation models for composite grounds and a practical project in Malaysia, followed by a comprehensive parametric study. The results demonstrate that soil anisotropy significantly affects compressibility, while anisotropy, clogging parameters, and stress dispersion exert a remarkable influence on both the consolidation behavior and the distribution of excess pore pressure in composite pile–improved ground.