A Micropolar Continuum Model Considering Anisotropy Evolution of Natural Clay and Finite Element Analysis of the Bearing Capacity of Structured Undrained Foundations

ABSTRACT This study deeply couples soil anisotropy theory related to the major principal stress direction with nonlinear strain‐softening formula. Then, an MC‐matched DP model considering anisotropy evolution is developed within the micropolar continuum framework. The model effectively captures how structural degradation in natural clay without distinct stratification leads to progressive strength reduction and diminishing anisotropy during shear deformation. Numerical implementation is achieved using the ABAQUS UEL subroutine, and its reliability is validated through comparisons with experimental data and existing literature. The analysis of strip foundation bearing capacity on structured clay using this model demonstrates that both soil strength anisotropy and strain softening significantly influence the ultimate bearing capacity factor N c , with their omission leading to overestimated results, particularly under smooth base conditions. Meanwhile, the anisotropy evolution has a significant impact on the residual value of the foundation bearing capacity. Variations in deposition angle () exhibit a non‐monotonic effect on N c , initially decreasing and then increasing, with the minimum occurring in the 40°–50° range. Changes in also induce a transition from a symmetric to an asymmetric shear band failure mode, although the residual bearing capacity remains largely unaffected. Progressive failure analysis reveals the coupled evolution of equivalent plastic strain, degree of anisotropy, and undrained shear strength, with their dynamic interactions corresponding to the characteristics of the bearing capacity‐displacement curve. A mesh sensitivity comparison further illustrates that, unlike the classical continuum model, which fails under refined meshing, the proposed micropolar continuum model demonstrates superior numerical convergence, ensuring stable and mesh‐independent solutions.