Coupling of hydraulic hysteresis and stress–strain behaviour in unsaturated soils
TL;DR: In this paper, a new elasto-plastic framework for unsaturated soils is proposed, involving coupling of hydraulic hysteresis and mechanical behaviour, and a specific constitutive model for isotropic stress states is proposed.
Abstract: Consideration of the different roles of pore air pressure, pore water pressure within bulk water and pore water pressure within meniscus water suggests that the degree of saturation will have a significant influence on the stress–strain behaviour of an unsaturated soil, in addition to any influence of suction. This suggestion is supported by experimental evidence. In the light of this, a new elasto-plastic framework for unsaturated soils is proposed, involving coupling of hydraulic hysteresis and mechanical behaviour. Within the proposed framework, plastic changes of degree of saturation influence the stress–strain behaviour, and plastic volumetric strains influence the water retention behaviour. A specific constitutive model for isotropic stress states is proposed, and model predictions are compared with experimental results, in order to demonstrate some of the capabilities of the new framework. Forms of behaviour that can be represented include proper transitions between saturated and unsaturated types ...
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24 Jul 2012TL;DR: This paper explains the nature of each of the previous challenges to the implementation of unsaturated soil mechanics, and the determination of indirect techniques for the estimation of uns saturated soil property functions.
Abstract: Unsaturated soil mechanics has rapidly become a part of geotechnical engineering practice as a result of solutions that have emerged to a number of key problems (or challenges). The solutions have emerged from numerous research studies focusing on issues that have a hindrance to the usage of unsaturated soil mechanics. The primary challenges to the implementation of unsaturated soil mechanics can be stated as follows: (1) The need to understand the fundamental, theoretical behavior of an unsaturated soil; (2) the formulation of suitable constitutive equations and the testing for uniqueness of proposed constitutive relationships; (3) the ability to formulate and solve one or more nonlinear partial differential equations using numerical methods; (4) the determination of indirect techniques for the estimation of unsaturated soil property functions, and (5) in situ and laboratory devices for the measurement of a wide range of soil suctions. This paper explains the nature of each of the previous challenges and...
562 citations
TL;DR: In this article, an elasto-plastic model for unsaturated soils is presented that takes explicitly into account the mechanisms with which suction affects mechanical behaviour as well as their dependence on degree of saturation.
Abstract: The paper presents an elasto-plastic model for unsaturated soils that takes explicitly into account the mechanisms with which suction affects mechanical behaviour as well as their dependence on degree of saturation. The proposed model is formulated in terms of two constitutive variables directly related to these suction mechanisms: the average skeleton stress, which includes the average fluid pressure acting on the soil pores, and an additional scalar constitutive variable, ξ, related to the magnitude of the bonding effect exerted by meniscus water at the inter-particle contacts. The formulation of the model in terms of variables closely related to specific behaviour mechanisms leads to a remarkable unification of experimental results of tests carried out with different suctions. The analysis of experimental isotropic compression data strongly suggests that the quotient between the void ratio, e, of an unsaturated soil and the void ratio es, corresponding to the saturated state at the same average soil sk...
541 citations
TL;DR: In this paper, the authors reviewed the applicability of Terzaghi's single effective stress principle for constitutive modelling purposes and its advantages for unsaturated soil modeling are reassessed in a comparative manner.
Abstract: 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.
476 citations
Cites methods from "Coupling of hydraulic hysteresis an..."
...[46] also make use of the work input considerations to justify their choice of the Bishop generalized effective stress and a second stress variable named the modified suction....
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TL;DR: In this article, an improved relationship for the variation of degree of saturation in an unsaturated soil is presented, incorporating the influence of changes of void ratio, when combined with an elasto-plastic stress-strain model.
Abstract: An improved relationship for the variation of degree of saturation in an unsaturated soil is presented, incorporating the influence of changes of void ratio. When combined with an elasto-plastic stress-strain model, this is able to represent irreversible changes of degree of saturation and changes of degree of saturation caused by shearing. Experimental data from tests on compacted Speswhite kaolin are used to demonstrate the success of the proposed new expression for degree of saturation. The experimental data involve a wide variety of stress paths, including wetting, isotropic loading and unloading under constant suction, constant suction shearing, and constant water content shearing. Improved representation of the variation of degree of saturation has important consequences for numerical modelling of coupled flow-deformation problems, where the expression used for the degree of saturation can influence significantly the suction generated within the soil and hence the predicted stress-strain behaviour.
393 citations
Cites background or methods from "Coupling of hydraulic hysteresis an..."
...A more difficult issue—that degree of saturation also appears to influence stress–strain behaviour—is starting to be tackled by authors such as Buisson & Wheeler (2000), Gallipoli et al. (2003) and Wheeler et al. (2003)....
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...This laboratory test was performed by Zakaria (1995), whereas all the other experimental tests presented here, including those used in the selection of parameter values, were performed by Sivakumar (1993)....
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TL;DR: In this paper, the effect of fly ash content on the free swell index, swell potential, swelling pressure, plasticity, compaction, strength, and hydraulic conductivity characteristics of expansive soil was evaluated.
Abstract: This note presents a study of the efficacy of fly ash as an additive in improving the engineering characteristics of expansive soils. An experimental program has evaluated the effect of the fly ash content on the free swell index, swell potential, swelling pressure, plasticity, compaction, strength, and hydraulic conductivity characteristics of expansive soil. The plasticity, hydraulic conductivity and swelling properties of the blends decreased and the dry unit weight and strength increased with an increase in fly ash content. The resistance to penetration of the blends increased significantly with an increase in fly ash content for a given water content. Excellent correlation was obtained between the measured and predicted undrained shear strengths.
348 citations
References
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01 Jan 1990
TL;DR: In this paper, a constitutive model for describing the stress-strain behavior of partially saturated soils is presented, formulated within the framework of hardening plasticity using two iodependent sets of stress variables: the excess of total stress over air pressure and the suction.
Abstract: The Paper presents a constitutive model for describing the stress-strain behaviour of partially saturated soils. The model is formulated within the framework of hardening plasticity using two iodependent sets of stress variables: the excess of total stress over air pressure and the suction. The mode1 is able to represent, in a consistent and unified manner, many of the fundamental features of the behaviour of partially saturated soils which had been treated separately by previously proposed models. On reaching saturation, the mode1 becomes a conventional critical state model. Because experimental evidence is still limited, the model has been kept as simple as possible in order to provide a basic framework from which extensions are possible. Tbe mode1 is intended for partially saturated soils which are slightly or moderately expansive. After formulating the model for isotropic and biaxial stress states, typical predictions are described and compared, in a qualitative way, with characteristic trends of the behaviour of partially saturated soils. Afterwards, the results of a number of suction-controlled laboratory tests on compacted kaolin and a sandy clay are used to evaluate the ability of the model to reproduce, quantitatively, observed behaviour. The agreement between observed and computed results is considered satisfactory and confirms the possibilities of reproducing the most important features of partially saturated soil behaviour using a simple general framework.
2,062 citations
TL;DR: In this paper, a constitutive model for describing the stress-strain behavior of partially saturated soils is presented, formulated within the framework of hardening plasticity using two independent sets of stress variables: the excess of total stress over air pressure and the suction.
Abstract: The Paper presents a constitutive model for describing the stress-strain behaviour of partially saturated soils. The model is formulated within the framework of hardening plasticity using two independent sets of stress variables: the excess of total stress over air pressure and the suction. The model is able to represent, in a consistent and unified manner, many of the fundamental features of the behaviour of partially saturated soils which had been treated separately by previously proposed models. On reaching saturation, the model becomes a conventional critical state model. Because experimental evidence is still limited, the model has been kept as simple as possible in order to provide a basic framework from which extensions are possible. The model is intended for partially saturated soils which are slightly or moderately expansive. After formulating the model for isotropic and triaxial stress states, typical predictions are described and compared, in a qualitative way, with characteristic trends of the...
2,041 citations
Journal Article•
967 citations
"Coupling of hydraulic hysteresis an..." refers methods in this paper
...The stress tensor ij has been used by authors such as Jommi & di Prisco (1994), Bolzon et al. (1996) and Gallipoli et al....
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...It is similar to the effective stress proposal of Bishop (1959), with his weighting factor, , replaced by Sr....
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TL;DR: In this paper, the tension in the air-water interface has been removed from Haines' formulae, and certain additional factors have also crept into his expressions for average stress.
Abstract: 1. The omission of the tension in the air-water interface has introduced an erroneous factor into Haines’ formulae; certain additional factors have also crept into his expressions for average stress.2. With these corrections, the stress due to moisture varies comparatively little with changing water content, though falling slightly throughout the range. The energy needed to cause rupture rises continuously in a manner not unlike Haines’ measurements, and should more probably be associated with them than should the tensile stress.3. The geometrical approximation used by Haines gives a close geometrical representation of the figure, but a mechanical approximation which is less satisfactory. Since neither the formulae connected with the true curve, nor the tables needed to use them, are readily, accessible, sufficiently exact numerical data have been here put on record.
562 citations
TL;DR: In this article, an improved relationship for the variation of degree of saturation in an unsaturated soil is presented, incorporating the influence of changes of void ratio, when combined with an elasto-plastic stress-strain model.
Abstract: An improved relationship for the variation of degree of saturation in an unsaturated soil is presented, incorporating the influence of changes of void ratio. When combined with an elasto-plastic stress-strain model, this is able to represent irreversible changes of degree of saturation and changes of degree of saturation caused by shearing. Experimental data from tests on compacted Speswhite kaolin are used to demonstrate the success of the proposed new expression for degree of saturation. The experimental data involve a wide variety of stress paths, including wetting, isotropic loading and unloading under constant suction, constant suction shearing, and constant water content shearing. Improved representation of the variation of degree of saturation has important consequences for numerical modelling of coupled flow-deformation problems, where the expression used for the degree of saturation can influence significantly the suction generated within the soil and hence the predicted stress-strain behaviour.
393 citations
"Coupling of hydraulic hysteresis an..." refers methods in this paper
...4 shows an example from a wetting– drying cycle performed by Sharma (1998) on a compacted bentonite–kaolin sample, tested under isotropic stress conditions (at a mean net stress of 10 kPa) in a triaxial cell....
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