Bounding surface rotational hardening model for overconsolidated clay accounting for evolving fabric anisotropy

Abstract

AbstractSoil is inherently anisotropic owing to the sedimentation process under gravity and is generally under anisotropic stress state in the field. To reflect the influence of anisotropic consolidation, rotational hardening (RH) is favorably used in constitutive models, mimicking in‐situ stress conditions. However, most of the existing models do not account for the inherent anisotropy of clays under isotropic stress state as well as the interplay between the fabric and loading direction, and the corresponding initial yield surface is assumed to be oriented along the hydrostatic axis. Furthermore, as the rotational angle is usually deemed as the clayed soil's anisotropy measure, a critical yield surface without rotation appears to contradict the highly anisotropic fabric at critical state. In this study, an anisotropic bounding surface model that incorporates RH and fabric anisotropy is formulated to simulate the behavior of overconsolidated (OC) clay subject to different consolidation histories, while addressing the aforementioned inconsistency issue. During the loading process, both fabric anisotropy and rotational angle evolve continuously based on their respective evolution rules. Fabric anisotropy evolves to the critical state when the rotational angle returns to zero, satisfying the anisotropic critical state theory (ACST). In addition, the model employs an anisotropic elasticity to consider the influence of the initial fabric at a low‐stress level. The predictive capacity of the model can be demonstrated by simulating several compression and extension tests on clay over a wide range of overconsolidation ratios (OCRs) and anisotropic consolidation stress ratios under both drained and undrained conditions.