Documents disponibles écrits par cet auteur

Engineering in stiff sedimentary clays / B. Simpson in Géotechnique, Vol. 60 N° 12 (Décembre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 12 (Décembre 2010) . - pp. 903–911 Titre : Engineering in stiff sedimentary clays Type de document : texte imprimé Auteurs : B. Simpson, Auteur Année de publication : 2011 Article en page(s) : pp. 903–911 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Geology  Constitutive  relations  Clays  Shear  strength  Laboratory  tests  Stiffness Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The papers to the Symposium in Print are reviewed, looking in particular for insights and applications available to practising designers.† The papers display the complexity of the behaviour of stiff clays, and the very high level of expertise committed to researching it. The features of behaviour described, and to some extent quantified, are very important in understanding observed phenomena in conventional civil engineering situations. Studies of the stratigraphy of London Clay, as an example, show some helpful consistency across the deposit when results are plotted relative to its base, but also show that it is not a single, uniform material. Engineering at greater depth and with thermal effects, as required for nuclear repositories, provides some new challenges, involving both unfamiliar parameters and more familiar problems of characterising stiffness, strength and permeability, especially in bonded materials, set in a context of higher stresses. The combination of high-quality laboratory studies with field observations of full-scale behaviour remains essential to the development of geotechnical engineering, and both are well represented in the papers to the Symposium. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.07.kp.002 [article] Engineering in stiff sedimentary clays [texte imprimé] / B. Simpson, Auteur . - 2011 . - pp. 903–911. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 12 (Décembre 2010) . - pp. 903–911 Mots-clés : Geology  Constitutive  relations  Clays  Shear  strength  Laboratory  tests  Stiffness Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The papers to the Symposium in Print are reviewed, looking in particular for insights and applications available to practising designers.† The papers display the complexity of the behaviour of stiff clays, and the very high level of expertise committed to researching it. The features of behaviour described, and to some extent quantified, are very important in understanding observed phenomena in conventional civil engineering situations. Studies of the stratigraphy of London Clay, as an example, show some helpful consistency across the deposit when results are plotted relative to its base, but also show that it is not a single, uniform material. Engineering at greater depth and with thermal effects, as required for nuclear repositories, provides some new challenges, involving both unfamiliar parameters and more familiar problems of characterising stiffness, strength and permeability, especially in bonded materials, set in a context of higher stresses. The combination of high-quality laboratory studies with field observations of full-scale behaviour remains essential to the development of geotechnical engineering, and both are well represented in the papers to the Symposium. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.07.kp.002

Influence of strain rate and acceleration on the behaviour of reconstituted clays at small strains / K. K. Sorensen in Géotechnique, Vol. 60 N° 10 (Octobre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 10 (Octobre 2010) . - pp. 751-763 Titre : Influence of strain rate and acceleration on the behaviour of reconstituted clays at small strains Type de document : texte imprimé Auteurs : K. K. Sorensen, Auteur ; B. A. Baudet, Auteur ; B. Simpson, Auteur Année de publication : 2011 Article en page(s) : pp. 751-763 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Clays  Stiffness  Time  dependence  Laboratory  tests  Dynamics  Creep Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper attempts to bridge the gap between the well-known characteristics of strain rate-independent elastic stiffness and of the time-dependent behaviour of clays at large strains. Effects of acceleration, strain rate and ageing are examined in the very small to small strain region, using results from tests on reconstituted London Clay and kaolin. Static measurements of the shear modulus at small strains, using local instrumentation, indicate that the shear modulus is rate-independent when the soil is subjected to elastic deformations only. Most often, in practice, soil specimens are left to rest between the compression and shearing stages, until deformations associated with creep become negligible. The testing strain rate imposed upon shearing induces a temporary acceleration of strains, which results in very high measured stiffnesses. Test data show, however, that when the shearing axial strain rate is of the same order of magnitude as that measured at the end of the compression/creep stage, the remaining plastic creep strains influence the measured stiffness, which is then measured to be comparatively low. Test data also seem to show that temporary strain acceleration may hide effects of recent stress path rotation. Additionally, bender element tests were performed during isotropic compression tests with changes in stress rate and creep stages. The data indicate that the strain rate affects the value of the dynamic shear modulus of the soil. It is suggested that the increase in dynamic shear modulus during short-term creep is caused by mechanisms linked to the gradual decrease in strain rate during creep, but further investigation would be needed to clarify which physical mechanisms. A new method to account for strain rate in evaluating the dynamic shear modulus of normally consolidated reconstituted clays is finally proposed. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.07.d.147 [article] Influence of strain rate and acceleration on the behaviour of reconstituted clays at small strains [texte imprimé] / K. K. Sorensen, Auteur ; B. A. Baudet, Auteur ; B. Simpson, Auteur . - 2011 . - pp. 751-763. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 10 (Octobre 2010) . - pp. 751-763 Mots-clés : Clays  Stiffness  Time  dependence  Laboratory  tests  Dynamics  Creep Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper attempts to bridge the gap between the well-known characteristics of strain rate-independent elastic stiffness and of the time-dependent behaviour of clays at large strains. Effects of acceleration, strain rate and ageing are examined in the very small to small strain region, using results from tests on reconstituted London Clay and kaolin. Static measurements of the shear modulus at small strains, using local instrumentation, indicate that the shear modulus is rate-independent when the soil is subjected to elastic deformations only. Most often, in practice, soil specimens are left to rest between the compression and shearing stages, until deformations associated with creep become negligible. The testing strain rate imposed upon shearing induces a temporary acceleration of strains, which results in very high measured stiffnesses. Test data show, however, that when the shearing axial strain rate is of the same order of magnitude as that measured at the end of the compression/creep stage, the remaining plastic creep strains influence the measured stiffness, which is then measured to be comparatively low. Test data also seem to show that temporary strain acceleration may hide effects of recent stress path rotation. Additionally, bender element tests were performed during isotropic compression tests with changes in stress rate and creep stages. The data indicate that the strain rate affects the value of the dynamic shear modulus of the soil. It is suggested that the increase in dynamic shear modulus during short-term creep is caused by mechanisms linked to the gradual decrease in strain rate during creep, but further investigation would be needed to clarify which physical mechanisms. A new method to account for strain rate in evaluating the dynamic shear modulus of normally consolidated reconstituted clays is finally proposed. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.07.d.147

A strain space soil model with evolving stiffness anisotropy / K. C. Ellison in Géotechnique, Vol. 62 N° 7 (Juillet 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 7 (Juillet 2012) . - pp. 627 –641 Titre : A strain space soil model with evolving stiffness anisotropy Type de document : texte imprimé Auteurs : K. C. Ellison, Auteur ; K. Soga, Auteur ; B. Simpson, Auteur Année de publication : 2012 Article en page(s) : pp. 627 –641 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Stiffness  Constitutive  relations  Anisotropy Résumé : A complete formulation of the BRICK soil model in general strain space is presented herein for the first time. Like all elasto-plastic constitutive models, BRICK exhibits some anisotropic behaviour, owing to the development of plastic strains once its yield surfaces are engaged. However, an abundance of laboratory and field evidence demonstrates that stiffness anisotropy is also significant within the elastic domain. Because of the inseparable nature of strength and stiffness in BRICK, the simple use of an anisotropic elastic stiffness matrix would result in an unrealistically high degree of strength anisotropy. Therefore, in addition to the established BRICK formulation, this paper also presents a novel framework to introduce stiffness anisotropy by transforming the coordinate system in which the model is based. The transformed coordinate system evolves to enable a constant-volume condition during shearing at critical state, reflecting the reorganisation of the soil fabric. The superior performance of the enhanced BRICK model over the classic model is demonstrated by a variety of conventional and non-conventional laboratory tests on London Clay. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.P.095 [article] A strain space soil model with evolving stiffness anisotropy [texte imprimé] / K. C. Ellison, Auteur ; K. Soga, Auteur ; B. Simpson, Auteur . - 2012 . - pp. 627 –641. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 7 (Juillet 2012) . - pp. 627 –641 Mots-clés : Stiffness  Constitutive  relations  Anisotropy Résumé : A complete formulation of the BRICK soil model in general strain space is presented herein for the first time. Like all elasto-plastic constitutive models, BRICK exhibits some anisotropic behaviour, owing to the development of plastic strains once its yield surfaces are engaged. However, an abundance of laboratory and field evidence demonstrates that stiffness anisotropy is also significant within the elastic domain. Because of the inseparable nature of strength and stiffness in BRICK, the simple use of an anisotropic elastic stiffness matrix would result in an unrealistically high degree of strength anisotropy. Therefore, in addition to the established BRICK formulation, this paper also presents a novel framework to introduce stiffness anisotropy by transforming the coordinate system in which the model is based. The transformed coordinate system evolves to enable a constant-volume condition during shearing at critical state, reflecting the reorganisation of the soil fabric. The superior performance of the enhanced BRICK model over the classic model is demonstrated by a variety of conventional and non-conventional laboratory tests on London Clay. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.P.095