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

Abstract

SUMMARYThe 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.

Simple Methodology to Obtain Critical State Parameters of Remolded Clays Under Normally Consolidated Conditions Using the Fall-Cone Test

“…5. It is worth mentioning that different researchers report M values for kaolin in the range of 0.65-1.16 (Schofield and Wroth 1968;Rossato et al 1992;Terzaghi et al 1996;Khalili et al 2004;Nuth and Laloui 2008), which matches fairly well with our results. Again, is possible to evaluate the effects of using Eq 6 instead of Eq 5 in the derivations presented.…”

Using Local Second Gradient Model and Shear Strain Localisation to Model the Excavation Damaged Zone in Unsaturated Claystone

“…In the present study, we extend the model to unsaturated conditions with a constant gas pressure and introduce the compressibility of the solid grain skeleton through Biot's coefficient. The total stress field is defined according to Bishop's postulate (Nuth and Laloui 2008), which corresponds to Biot's definition and takes into account partial saturation :…”

Behaviour of Unsaturated Aggregated Soil in Oedometric Condition

“…v, which is the Bishop's eŠective stress with the Bishop's coe‹cient being the degree of saturation, is used for analysis of the results (Bishop, 1959;Nuth and Laloui, 2008) …”