A constitutive model for structured soils

Abstract

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).