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The Modified Cam Clay model is extended to account for the behaviour of unsaturated soils using Bishop’s stress. To describe the Loading – Collapse behaviour, the model incorporates a compressibility framework with suction and degree of saturation dependent compression lines. For simplicity, the present paper describes the model in the triaxial stress space with characteristic simulations of constant suction compression and triaxial tests, as well as wetting tests. The model reproduces an evolving post yield compressibility under constant suction compression, and thus, can adequately describe a maximum of collapse.

This paper presents a generalized effective stress model for describing the rate-independent behavior of normally to moderately overconsolidated clays (with OCRs less than 8) that exhibit normalized behavior. The model formulation comprises three components: (1) An elastoplastic model for normally consolidated clay including anisotropic and strain-softening behavior; (2) equations to describe the small strain nonlinearity and hysteretic response in unloading and reloading; and (3) bounding surface plasticity for irrecoverable, anisotropic, and path-dependent behavior of overconsolidated clays. Model complexity is controlled through the use of input parameters that can be obtained from a small number of standard soil tests. A complete procedure is described to select the input parameters for a given clay. A detailed assessment of the predictive capabilities and limitations of the proposed model is presented in a companion paper.

Summary: The paper describes and evaluates an incremental plasticity constitutive model for unsaturated, anisotropic, nonexpansive soils (CMUA). It is based on the modified Cam‐Clay (MCC) model for saturated soils and enhances it by introducing anisotropy (via rotation of the MCC yield surface) and an unsaturated compressibility framework describing a double dependence of compressibility on suction and on the degree of saturation of macroporosity. As the anisotropic and unsaturated features can be activated independently, the model is downwards compatible with the MCC model. The CMUA model can simulate effectively: the dependence of compressibility on the level of developed anisotropy, uniqueness of critical state independent of the initial anisotropy, an evolving compressibility during constant suction compression, and a maximum of collapse. The model uses Bishop's average skeleton stress as its first constitutive variable, favouring its numerical implementation in commercial numerical analysis codes (eg, finite element codes) and a unified treatment of saturated and unsaturated material states. [ABSTRACT FROM AUTHOR]