Effective stress concept in unsaturated soils: Clarification and validation of a unified framework

• Published in: International journal for numerical and analytical methods in geomechanics Vol. 32; no. 7; pp. 771 - 801
• Main Authors: Nuth, Mathieu, Laloui, Lyesse
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-05-2008; Wiley
• Subjects: Applied sciences; Buildings. Public works; Computation methods. Tables. Charts; constitutive modelling; critical state; effective stress; Exact sciences and technology; Geotechnics; Soil investigations. Testing; Soil mechanics. Rocks mechanics; stress framework; Structural analysis. Stresses; unsaturated soils; Constitutive equation; unsaturated soils; Critical state; Stress analysis; Modeling; Soil mechanics; Characterization; Effective stress; constitutive modelling; Soil test; Formulation; Unsaturated soil; stress framework
• ISSN: 0363-9061; 1096-9853
• DOI: 10.1002/nag.645

The effective stress principle, conventionally applied in saturated soils, is reviewed for constitutive modelling purposes. The assumptions for the applicability of Terzaghi's single effective stress are recalled and its advantages are inventoried. The possible stress frameworks applicable to unsaturated soil modelling are reassessed in a comparative manner, specifically the Bishop's single effective stress, the independent stress variables approach and the generalized stress framework. The latter considerations lead to the definition of a unified stress context, suitable for modelling soils under different saturation states. In order to qualify the implications brought by the proposed stress framework, several experimental data sets are re‐examined in the light of the generalized effective stress. The critical state lines (CSLs) at different saturation states tend to converge remarkably towards a unique saturated line in the deviatoric stress versus mean effective stress plane. The
effective stress interpretation is also applied to isotropic paths and compared with conventional net stress conception. The accent is finally laid on a second key feature for constitutive frameworks based on a unified stress, namely the sufficiency of a unique mechanical yield surface besides the unique CSL. Copyright © 2007 John Wiley & Sons, Ltd.