An unsaturated soil model with minimal number of parameters based on bounding surface plasticity

Morvan, Mathilde; Wong, Henry; Branque, Denis

doi:10.1002/nag.871

Cited by 46 publications

(39 citation statements)

References 38 publications

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“…The concept of yield stress in classical elastoplasticity theory refers to the stress level that causes plastic deformation. In other plasticity frameworks such as bounding surface plasticity [21,99,78], hypoplasticity [60,72] and generalised plasticity [69,86,101], plastic deformation occurs along all loading paths including reloading. In these cases, a loading function or a bounding surface is used to differentiate unloading from loading.…”

Section: Relationship Between Yield Stress and Volume Change Equationmentioning

confidence: 99%

Review of fundamental principles in modelling unsaturated soil behaviour

Sheng

2011

Computers and Geotechnics

206

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Section: Relationship Between Yield Stress and Volume Change Equationmentioning

confidence: 99%

Review of fundamental principles in modelling unsaturated soil behaviour

Sheng

2011

Computers and Geotechnics

206

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“…This couple has also been adopted by Cui et al (1995) and Sheng et al (2008). Another possibility can be a particular effective stress adapted to unsaturated soils and suction (Coussy and Dangla 2002;Loret and Khalili 2002;Pereira et al 2005;Russell and Khalili 2006;Morvan et al 2010). A summary of the methods of constitutive modeling is given in Sheng (2011).…”

Section: Introductionmentioning

confidence: 91%

“…This initial model was validated by comparison to experimental data on silt and sands (Morvan 2010;Morvan et al 2010). These experimental data were taken from the work of Cui and Delage (1996) and Russell and Khalili (2006).…”

Section: ½25mentioning

confidence: 99%

“…The first version of this model (by Morvan et al in 2010) only required 12 parameters for its definition, and yet can simulate a few behaviors typically observed on unsaturated fine sands, which more classical models fail to reproduce. These include post-peak softening, change from contractant to dilatant behavior during shearing, and the smooth transition from elastic to elastoplastic behavior upon yielding.…”

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confidence: 98%

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Incorporating porosity-dependent hysteretic water retention behavior into a new constitutive model of unsaturated soils

2011

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A new unsaturated soil model was recently developed at Ecole Nationale des Travaux Publics de l'Etat (ENTPE), based on the concept of bounding surface plasticity. The first version of this model (by Morvan et al. in 2010) only required 12 parameters for its definition, and yet can simulate a few behaviors typically observed on unsaturated fine sands, which more classical models fail to reproduce. These include post-peak softening, change from contractant to dilatant behavior during shearing, and the smooth transition from elastic to elastoplastic behavior upon yielding. Subsequent to this first publication, additional mechanisms have been introduced in the model previously developed. Among them, the hysteretic phenomenon during cyclic variations of suction and water content, as well as the effects of porosity change on water retention characteristics, are now taken into consideration. To this end, the water content is introduced as an independent generalized strain variable, which is no longer uniquely linked to suction. Thanks to these developments, the model can now account for the bilateral couplings between hydraulic and mechanical quantities, with good precision under very general loading conditions. In the present paper, these new developments are presented in detail, and the experimental basis of this construction is discussed. The model is then validated using existing experimental data on kaolin, by considering two stress paths. The first stress path consists of a single cycle of wetting followed by drying at constant isotropic stress. The second, more complex loading path involves simultaneous variations of suction and isotropic compression or decompression. The results confirm overall the satisfactory performance of the model. The main conclusions are then summarized in the last section, including perspectives for future developments.Résumé : Un nouveau modèle de sol non saturé a été développé récemment à Ecole Nationale des Travaux Publics de l'Etat (l'ENTPE), selon le concept de la surface limite de plasticité. La première version de ce modèle (par Morvan et al. en 2010) nécessitait seulement 12 paramètres pour sa définition, mais pouvait tout de même simuler quelques comportements typiques observés sur des sables non saturés dont les modèles plus classiques n'arrivaient pas à reproduire. Ceux-ci incluent l'adoucissement post-pic, le changement d'un comportement contractant à un comportement dilatant durant le cisaillement, et la transition graduelle d'un comportement élastique à élasto-plastique à la limite élastique. Suite à cette première publication, des mécanismes additionnels ont été introduits au modèle développé précédemment. Parmi ces mécanismes, le phéno-mène d'hystérésis durant les variations cycliques de la succion et de la teneur en eau, et les effets de la variation de la porosité sur les caractéristiques de rétention d'eau, sont maintenant considérés. Ainsi, la teneur en eau est introduite en tant que variable indépendante généralisée de la déformation qui n'est plus seulement liée à l...

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“…Triaxial apparatus allows us to rebuild samples but also to work on undisturbed samples, so each case can occur. We choose BDNS model [16] for this calculation. In this model, enlarged effective stress concept is used as well as the bounding surface theory that permits a smooth transition between elastic and plastic domains.…”

Section: Elastoplastic Simulationmentioning

confidence: 99%

Study of the variation of B with Sr

2016

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Abstract. Skempton coefficient B is commonly used to verify the saturation of a sample before triaxial testing. This coefficient is obtained during undrained isotropic consolidation and is defined as the ratio between the increment of pore pressure u measured and the imposed increment of isotropic stress. This coefficient varies between 0 for dry soils and 1 for saturated soils. Many studies on liquefaction of unsaturated soils were published using Skempton coefficient B to represent saturation degree Sr of soil. On the first hand, this variation of B coefficient with saturation degree is mostly due to the compressibility of air in the pores. On the second hand, we also know that the presence of air as a fluid phase gives birth to suction after equilibrium is reached inside the sample. The higher the suction, the stiffer the soil skeleton. These two phenomena are opposite. Their effects in laboratory testing depend on the experimental apparatus. For example, if we consider an unsaturated triaxial device, we will have to take suction into account. On the contrary if we plan to break the menisci just before measuring B, suction equilibration will not occur. Experimental tests were performed to show the difference between these two cases and to study the equilibrium phase. Based on these observations, this article presents new relationships that permit to calculate saturation degree with a given Skempton coefficient with different hypotheses and with different experimental devices. These results are confronted to the commonly used relation given by Lade and the difference between all these calculations is studied.

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An unsaturated soil model with minimal number of parameters based on bounding surface plasticity

Cited by 46 publications

References 38 publications

Review of fundamental principles in modelling unsaturated soil behaviour

Review of fundamental principles in modelling unsaturated soil behaviour

Incorporating porosity-dependent hysteretic water retention behavior into a new constitutive model of unsaturated soils

Study of the variation of B with Sr

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