An extended generalized effective stress for active clays

Angelica Tuttolomondo,Lyesse Laloui,Alessio Ferrari,R Cardoso,C Jommi,E Romero

doi:10.1051/e3sconf/202019502004

Angelica Tuttolomondo, Lyesse Laloui + Show 4 more

Open Access

https://doi.org/10.1051/e3sconf/202019502004

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Abstract

An effective stress concept for active clays is formulated to improve the modelling of these materials under a variety of environmental conditions. In particular, the mechanical effects induced by a change in the chemical potential of pore water associated with a change of its pressure (even in the negative range), as well as a change of its chemical composition, are considered. Some implications of the proposed framework are shown with reference to shear strength results related to unsaturated conditions. The proposed approach allows to describe the shear strength envelope consistently by using a unique set of shear strength parameters irrespective of the pore water chemical composition and of the saturation state.

Highlights

Active clays are often one of the geological barriers within nuclear waste storage repositories or one of the layers within geosynthetic liners used in a variety of containment applications
The chemical potential of the pore water within the representative elementary volume of a geomaterial depends on its: (i) pressure (ii) temperature (iii) activity; activity, in turn, can be a function of pressure, temperature, chemical composition and of the presence of liquid-gas interfaces related to a pore water pressure lower than the pressure of the gas phase
With specific reference to the chemical composition of the pore water, experimental studies available in literature show that the effect of its variation is the more significant the more active the clay is

Summary

Introduction

Active clays are often one of the geological barriers within nuclear waste storage repositories or one of the layers within geosynthetic liners used in a variety of containment applications. Any variation in the chemical potential of pore water, related to one of the above-mentioned factors, typically affects the mechanical response of the involved geomaterial, with reference to shear strength and volumetric behaviour both An advanced geomechanical approach should take all these aspects into account for a comprehensive description of the mechanical behaviour of clays, especially if active To this end, there is a need for: (i) an effective stress variable (defined on as the single mechanical stress variable) suitable for governing the strains of the solid skeleton, including the strains induced by a change of the chemical potential of the pore water; (ii) the definition of the stress variables (hydraulic or electrochemical in nature) and the corresponding stress-strain type constitutive relations necessary for the determination of the effective stress at any state; (iii) a suitable constitutive context [8]. The performances of the framework are revealed by referring to shear strength data at negative pore water pressures (positive matric suction values)

The extended generalized effective stress concept

Conclusions