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Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 1, Wetting and compression behaviour / V. Sivakumar in Géotechnique, Vol. 60 N° 8 (Août 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 581–594 Titre : Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 1, Wetting and compression behaviour Type de document : texte imprimé Auteurs : V. Sivakumar, Auteur ; R. Sivakumar, Auteur ; E. J. Murray, Auteur Année de publication : 2011 Article en page(s) : pp. 581–594 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Clays  Laboratory  tests  Stress  path  Compaction  Anisotropy  Earth  fill Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Over the last 40 years considerable progress has been made in understanding the complex behaviour of unsaturated soils. Research using constitutive modelling has extended the critical state framework and the concept of yielding in saturated soils to encompass unsaturated soils experiencing suction. However, validation testing of the framework for unsaturated soils has shown disagreement with the basic propositions. The main reason for this disparity is the anisotropic properties of the soil specimens tested as a result of preparation using one-dimensional compaction. The paper describes the detailed testing carried out to justify this statement. As part of the work presented, samples of unsaturated kaolin were prepared using isotropic compression. The suctions in these samples were reduced to predefined values by wetting under low isotropic loading. The pore size distributions, the pressure–volume relationships and yielding under subsequent isotropic loading are compared with tests on samples prepared by statically compressing kaolin into a one-dimensional compaction mould. The anisotropically compressed samples had initial water contents and specific volumes similar to those of the isotropically prepared samples and were also tested under reducing suctions; they exhibited distinctly different behaviour when tested under similar conditions. The results obtained from the isotropically prepared and tested samples have shown, probably for the first time, the existence of a unique normal compression surface that is not dependent on the initial conditions of the samples. The shape of the loading–collapse (LC) yield locus is shown to be different from the generally accepted form. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.007 [article] Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 1, Wetting and compression behaviour [texte imprimé] / V. Sivakumar, Auteur ; R. Sivakumar, Auteur ; E. J. Murray, Auteur . - 2011 . - pp. 581–594. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 581–594 Mots-clés : Clays  Laboratory  tests  Stress  path  Compaction  Anisotropy  Earth  fill Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Over the last 40 years considerable progress has been made in understanding the complex behaviour of unsaturated soils. Research using constitutive modelling has extended the critical state framework and the concept of yielding in saturated soils to encompass unsaturated soils experiencing suction. However, validation testing of the framework for unsaturated soils has shown disagreement with the basic propositions. The main reason for this disparity is the anisotropic properties of the soil specimens tested as a result of preparation using one-dimensional compaction. The paper describes the detailed testing carried out to justify this statement. As part of the work presented, samples of unsaturated kaolin were prepared using isotropic compression. The suctions in these samples were reduced to predefined values by wetting under low isotropic loading. The pore size distributions, the pressure–volume relationships and yielding under subsequent isotropic loading are compared with tests on samples prepared by statically compressing kaolin into a one-dimensional compaction mould. The anisotropically compressed samples had initial water contents and specific volumes similar to those of the isotropically prepared samples and were also tested under reducing suctions; they exhibited distinctly different behaviour when tested under similar conditions. The results obtained from the isotropically prepared and tested samples have shown, probably for the first time, the existence of a unique normal compression surface that is not dependent on the initial conditions of the samples. The shape of the loading–collapse (LC) yield locus is shown to be different from the generally accepted form. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.007

Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 2, Performance under shear loading / V. Sivakumar in Géotechnique, Vol. 60 N° 8 (Août 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 595–609 Titre : Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 2, Performance under shear loading Type de document : texte imprimé Auteurs : V. Sivakumar, Auteur ; R. Sivakumar, Auteur ; J. Boyd, Auteur Année de publication : 2011 Article en page(s) : pp. 595–609 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Suction  Stress  path  Compaction  Unsaturation  Shear  strength Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Validation of a framework for unsaturated soil behaviour has frequently resulted in disagreement with basic propositions. A primary reason for this disparity is considered to be attributable to the anisotropic properties of the soil specimens tested as a result of preparation using one-dimensional compaction. As part of the work presented, comparison is made between tests on samples of unsaturated kaolin prepared at identical specific volumes and specific water volumes using isotropic compression and one-dimensional compression. The suctions in the samples were reduced to predefined values by wetting under low isotropic loading in a triaxial cell. The samples were then taken through various stress paths to failure, defined as the critical state strength, while the suctions were held constant. Stress path tests were also performed on samples without reducing the suction to predefined values. In the latter, constant water mass tests, the suctions were allowed to vary and were measured using a psychrometer. The results of the tests at critical state are compared with the propositions of Wheeler and Sivakumar. The shear strengths of samples with isotropic previous history are shown to be significantly greater than those of samples with one-dimensional stress history when plotted against the mean net stress. The normal compression lines, critical state lines and yield characteristics are also shown to be significantly influenced by the previous stress history and are shown to be different for isotropically and one-dimensionally prepared samples. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.008 [article] Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 2, Performance under shear loading [texte imprimé] / V. Sivakumar, Auteur ; R. Sivakumar, Auteur ; J. Boyd, Auteur . - 2011 . - pp. 595–609. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 595–609 Mots-clés : Suction  Stress  path  Compaction  Unsaturation  Shear  strength Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Validation of a framework for unsaturated soil behaviour has frequently resulted in disagreement with basic propositions. A primary reason for this disparity is considered to be attributable to the anisotropic properties of the soil specimens tested as a result of preparation using one-dimensional compaction. As part of the work presented, comparison is made between tests on samples of unsaturated kaolin prepared at identical specific volumes and specific water volumes using isotropic compression and one-dimensional compression. The suctions in the samples were reduced to predefined values by wetting under low isotropic loading in a triaxial cell. The samples were then taken through various stress paths to failure, defined as the critical state strength, while the suctions were held constant. Stress path tests were also performed on samples without reducing the suction to predefined values. In the latter, constant water mass tests, the suctions were allowed to vary and were measured using a psychrometer. The results of the tests at critical state are compared with the propositions of Wheeler and Sivakumar. The shear strengths of samples with isotropic previous history are shown to be significantly greater than those of samples with one-dimensional stress history when plotted against the mean net stress. The normal compression lines, critical state lines and yield characteristics are also shown to be significantly influenced by the previous stress history and are shown to be different for isotropically and one-dimensionally prepared samples. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.008

Thermomechanical state parameter models for sands / I. F. Collins in Géotechnique, Vol. 60 N° 8 (Août 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 611–622 Titre : Thermomechanical state parameter models for sands Type de document : texte imprimé Auteurs : I. F. Collins, Auteur ; B. Muhunthan, Auteur ; B. Qu, Auteur Année de publication : 2011 Article en page(s) : pp. 611–622 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Plasticity  Thermomechanics  sands  State  parameters  Constitutive  relations  Anisotropy Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The granular structure of sands and other geomaterials makes them amongst the most difficult engineering materials to model. In this paper a recently developed thermomechanical procedure is used to derive constitutive models for sands undergoing triaxial deformations. The well-known geomechanical state parameter is given a new significance and is taken as the fundamental thermomechanical state parameter. The logarithm of the specific volume is shown to be the plastic volume strain, and its relationship to the logarithm of the effective pressure is shown to be fractal. In addition the shear-induced volume strains, characteristic of granular materials, are introduced via a workless constraint, and the resulting deformation is seen to exhibit ‘induced anisotropy' automatically. The associated reaction stress tensor is shown to be identical with the extant fabric tensor. The plastic flow rule is shown to be necessarily non-associated. Comparison with experimental data is made, together with some discussion of the model's relation to the predictions of distinct element simulations. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.127 [article] Thermomechanical state parameter models for sands [texte imprimé] / I. F. Collins, Auteur ; B. Muhunthan, Auteur ; B. Qu, Auteur . - 2011 . - pp. 611–622. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 611–622 Mots-clés : Plasticity  Thermomechanics  sands  State  parameters  Constitutive  relations  Anisotropy Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The granular structure of sands and other geomaterials makes them amongst the most difficult engineering materials to model. In this paper a recently developed thermomechanical procedure is used to derive constitutive models for sands undergoing triaxial deformations. The well-known geomechanical state parameter is given a new significance and is taken as the fundamental thermomechanical state parameter. The logarithm of the specific volume is shown to be the plastic volume strain, and its relationship to the logarithm of the effective pressure is shown to be fractal. In addition the shear-induced volume strains, characteristic of granular materials, are introduced via a workless constraint, and the resulting deformation is seen to exhibit ‘induced anisotropy' automatically. The associated reaction stress tensor is shown to be identical with the extant fabric tensor. The plastic flow rule is shown to be necessarily non-associated. Comparison with experimental data is made, together with some discussion of the model's relation to the predictions of distinct element simulations. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.127

A shear-displacement criterion for soil-infilled rock discontinuities / B. Indraratna in Géotechnique, Vol. 60 N° 8 (Août 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 623–633 Titre : A shear-displacement criterion for soil-infilled rock discontinuities Type de document : texte imprimé Auteurs : B. Indraratna, Auteur ; D. A. F. Oliveira, Auteur ; E. T. Brown, Auteur Année de publication : 2011 Article en page(s) : pp. 623–633 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Shear  strength  Clays  Laboratory  tests  Rocks/rock  mechanics Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : An infilled rock joint is likely to be the weakest plane in a rock mass. The most pronounced effect of the presence of infill material is the reduction in friction of the discontinuity boundaries (i.e. rock to rock contact of the joint walls). The thicker the infill, the smaller the shear strength of the rock joint. Once the infill reaches a critical thickness, the joint walls (rock) play no significant role in the overall shear strength. Several models have been proposed to predict the peak shear strength of infilled joints under both constant normal load and constant normal stiffness boundary conditions, taking into account the ratio of infill thickness (t) to the height of the joint wall asperity (a), that is the t/a ratio. Models based on the constant normal stiffness condition provide a much more accurate representation of the infilled joint behaviour in the field, but only a limited number of studies have focused on the more realistic constant normal stiffness stress–strain behaviour. This paper presents a critical review of some of the earlier studies and the most recent advancement of a shear-strength model developed at University of Wollongong, Australia, supplemented with laboratory data for model validation. The effect of different factors on the shear behaviour such as the t/a ratio, infill friction angle, joint wall roughness, joint stiffness and type of infill are presented. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.094 [article] A shear-displacement criterion for soil-infilled rock discontinuities [texte imprimé] / B. Indraratna, Auteur ; D. A. F. Oliveira, Auteur ; E. T. Brown, Auteur . - 2011 . - pp. 623–633. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 623–633 Mots-clés : Shear  strength  Clays  Laboratory  tests  Rocks/rock  mechanics Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : An infilled rock joint is likely to be the weakest plane in a rock mass. The most pronounced effect of the presence of infill material is the reduction in friction of the discontinuity boundaries (i.e. rock to rock contact of the joint walls). The thicker the infill, the smaller the shear strength of the rock joint. Once the infill reaches a critical thickness, the joint walls (rock) play no significant role in the overall shear strength. Several models have been proposed to predict the peak shear strength of infilled joints under both constant normal load and constant normal stiffness boundary conditions, taking into account the ratio of infill thickness (t) to the height of the joint wall asperity (a), that is the t/a ratio. Models based on the constant normal stiffness condition provide a much more accurate representation of the infilled joint behaviour in the field, but only a limited number of studies have focused on the more realistic constant normal stiffness stress–strain behaviour. This paper presents a critical review of some of the earlier studies and the most recent advancement of a shear-strength model developed at University of Wollongong, Australia, supplemented with laboratory data for model validation. The effect of different factors on the shear behaviour such as the t/a ratio, infill friction angle, joint wall roughness, joint stiffness and type of infill are presented. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.094

Influence of large-scale inhomogeneities on a construction dewatering system in chalk / M. A. Bevan in Géotechnique, Vol. 60 N° 8 (Août 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 635–649 Titre : Influence of large-scale inhomogeneities on a construction dewatering system in chalk Type de document : texte imprimé Auteurs : M. A. Bevan, Auteur ; W. Powrie, Auteur ; T. O. L. Roberts, Auteur Année de publication : 2011 Article en page(s) : pp. 635–649 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Numerical  modelling  Excavation  Permeability  Geology  Groundwater Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Large-scale anisotropy and inhomogeneities resulting from the presence of fissures, fractures and high-permeability zones can have a major impact on local groundwater flows, and affect significantly the performance of a construction dewatering system. A groundwater model for the HS1 Channel tunnel rail link Thames tunnel southern approach excavation is used to show that the observed performance of the construction dewatering system cannot adequately be explained unless such features are incorporated. While experience suggested that such features were likely to be present in this geological setting, at the design stage there was significant uncertainty regarding their scale. Groundwater flow modelling enabled the location and extent of the inhomogeneities present to be deduced in some detail. Features such as highly permeable zones might be identified by more thorough site investigation, including the more widespread use of pumping tests. However, the influence of anisotropy is harder to establish, primarily because its effect is most significant once a horizontal flow barrier (for example, a retaining wall) is in place, which is generally not the case during site investigation. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.010 [article] Influence of large-scale inhomogeneities on a construction dewatering system in chalk [texte imprimé] / M. A. Bevan, Auteur ; W. Powrie, Auteur ; T. O. L. Roberts, Auteur . - 2011 . - pp. 635–649. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 635–649 Mots-clés : Numerical  modelling  Excavation  Permeability  Geology  Groundwater Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Large-scale anisotropy and inhomogeneities resulting from the presence of fissures, fractures and high-permeability zones can have a major impact on local groundwater flows, and affect significantly the performance of a construction dewatering system. A groundwater model for the HS1 Channel tunnel rail link Thames tunnel southern approach excavation is used to show that the observed performance of the construction dewatering system cannot adequately be explained unless such features are incorporated. While experience suggested that such features were likely to be present in this geological setting, at the design stage there was significant uncertainty regarding their scale. Groundwater flow modelling enabled the location and extent of the inhomogeneities present to be deduced in some detail. Features such as highly permeable zones might be identified by more thorough site investigation, including the more widespread use of pumping tests. However, the influence of anisotropy is harder to establish, primarily because its effect is most significant once a horizontal flow barrier (for example, a retaining wall) is in place, which is generally not the case during site investigation. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.010

Experimental analysis of the cyclic behaviour of kaolin at high temperature / C. Cekerevac in Géotechnique, Vol. 60 N° 8 (Août 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 651–655 Titre : Experimental analysis of the cyclic behaviour of kaolin at high temperature Type de document : texte imprimé Auteurs : C. Cekerevac, Auteur ; L. Laloui, Auteur Année de publication : 2011 Article en page(s) : pp. 651–655 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Shear  strength  Liquefaction  Clays  Laboratory  tests  Temperature  effects  Earthquakes Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper presents the results of an experimental study related to thermal effects on kaolin clay cyclic mobility. The thermal effects were identified by comparing the experimental results of cyclic triaxial tests performed at high temperature (90°C) with results of the same type of test carried out at ambient temperature (22°C). For the testing, a new temperature-controlled triaxial apparatus, developed by the authors, was employed. Experimental evidence shows that shear cycles on the heated samples induced smaller axial strain and pore-water pressure per cycle in comparison with the unheated samples. In addition, shear-induced pore-water pressure at large strains in the heated sample was slightly lower than in the unheated sample. In other words, the heated samples behaved as if they were denser, which is a result of thermal hardening. These results may be applied in geotechnical and earthquake engineering applications as a soil improvement technique. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.7.00017 [article] Experimental analysis of the cyclic behaviour of kaolin at high temperature [texte imprimé] / C. Cekerevac, Auteur ; L. Laloui, Auteur . - 2011 . - pp. 651–655. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 8 (Août 2010) . - pp. 651–655 Mots-clés : Shear  strength  Liquefaction  Clays  Laboratory  tests  Temperature  effects  Earthquakes Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper presents the results of an experimental study related to thermal effects on kaolin clay cyclic mobility. The thermal effects were identified by comparing the experimental results of cyclic triaxial tests performed at high temperature (90°C) with results of the same type of test carried out at ambient temperature (22°C). For the testing, a new temperature-controlled triaxial apparatus, developed by the authors, was employed. Experimental evidence shows that shear cycles on the heated samples induced smaller axial strain and pore-water pressure per cycle in comparison with the unheated samples. In addition, shear-induced pore-water pressure at large strains in the heated sample was slightly lower than in the unheated sample. In other words, the heated samples behaved as if they were denser, which is a result of thermal hardening. These results may be applied in geotechnical and earthquake engineering applications as a soil improvement technique. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.7.00017

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