Structured clays exhibit engineering properties distinctly different from remoulded soils due to their unique cementation structure and spatial particle arrangement. By analysing the structural evolution characteristics of structured clay during isotropic compression

this study proposes a mathematical model for structural evolution based on yield stress. The model directly utilizes yield stress as a parameter characterizing initial structure

eliminating the need for additional initial structural parameters. Through analysis of compression curves

a relationship between structural evolution and yield stress was established

and a structural evolution mechanism influenced by both plastic volumetric strain and plastic deviatoric strain was introduced. Based on this foundation

the structural evolution model was incorporated into a unified hardening model framework

resulting in an elastoplastic constitutive model that comprehensively considers both initial state and structure. Beyond the parameters of the modified Cam-clay model

this structural model requires only 4 additional parameters

all obtainable through conventional physical and mechanical tests. The predictive capability of the model was verified by simulating compression and shearing processes of a hypothetical soil. Results demonstrate that the model accurately describes mechanical and deformation characteristics of compacted structured clay

including nonlinear volumetric compression

deviatoric stress peaks and strain softening during shearing

and structural evolution with plastic volumetric and deviatoric strains. The applicability and validity of the model were further verified through comparison with experimental data from various structured soils

including Jingyang loess

under different stress paths. The research findings provide a new theoretical perspective for understanding the mechanical behaviour of compacted structured soils

offering practical guidance for engineering applications in regions with structured clay deposits.