The paper proposes a constitutive model for structured soils (MSS) which describes the engineering effects of structure development and degradation, such as: high intact stiffness and strength, appreciable reduction of stiffness and strength due to de-structuring, and evolution of stress- and structure-induced anisotropy. A key feature of the model is the treatment of pre-consolidation as a structure-inducing process and the unified description of all such processes via a ‘bond strength envelope’ associated with the onset of appreciable de-structuring and distinguished from the onset of plastic yielding. Other features include: a damage-type mechanism to model volumetric and deviatoric structure degradation, the evolution of stress- and bond-induced anisotropy using a fading memory scheme, adaptable predictive capabilities depending on the sophistication of the available test data, modularity to extend its applicability in several soil types, and mathematical formulation in a general tensorial space to facilitate its incorporation in finite element codes. The predictive capabilities of the model are evaluated against the results of laboratory tests on the stiff overconsolidated Vallericca clay: (a) isotropic and anisotropic consolidation tests up to very high pressures; and (b) anisotropically consolidated triaxial shearing at both low pressures (structured material response) and high pressures (de-structured material response).

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.

The paper studies the seismic behaviour of an existing homogeneous earth dam using a fully coupled finite-element effective stress approach in conjunction with a recently developed multi-surface, elasto-plastic constitutive model for structured soils. The model is calibrated using laboratory test results for the embankment material and the foundation soils. The initial state variables (stress, hardening parameters) are determined by simulating a simplified geological history of the foundation soil, dam construction stages and reservoir impounding, prior to the application of the earthquake shaking at the bedrock level. The paper critically reviews the role of the constitutive model parameters, the hysteretic damping introduced by the model and the additional viscous damping parameters in the accumulation of permanent displacements and in the development and subsequent dissipation of excess pore water pressures due to the seismic loading. The analyses, carried out with reference to a set of earthquake records related to different return periods, show that the overall behaviour of the system in terms of displacements is characterised by a more enhanced deformation pattern of the downstream slope as compared with the upstream one. The large plastic strains accumulation induced throughout the shaking is followed by the development of excess pore water pressures inside the dam and the foundation deposit. Nonetheless, the results are indicative of a satisfactory dynamic performance of the dam, even when subjected to severe seismic loading conditions.