Documents disponibles écrits par cet auteur

Effect of loading mode on strain softening and instability behavior of sand in plane-strain tests / J. Chu in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N°1 (Janvier 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N°1 (Janvier 2009) . - pp. 108–120 Titre : Effect of loading mode on strain softening and instability behavior of sand in plane-strain tests Type de document : texte imprimé Auteurs : J. Chu, Auteur ; D. Wanatowski, Auteur Année de publication : 2009 Article en page(s) : pp. 108–120 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Sand  Laboratory  tests  Plane  strain  Strain  softening Résumé : Experimental data to study the effect of loading mode on the strain softening and instability behavior of sand under plane-strain conditions are presented in this paper. A new plane-strain apparatus was adopted to conduct K0 consolidated drained and undrained tests under both deformation-controlled and load-controlled loading modes. The drained behavior of very loose and medium dense sand and the undrained behavior of very loose sand under plane-strain conditions were characterized. The test results show that the loading mode affects the postpeak behavior and controls whether strain softening or instability will occur in the postpeak region. Shear bands occurred in tests conducted on medium dense sand, but not in tests for very loose sand. The failure line and critical state line are not affected by the loading mode. The study also shows that the concept of a unique “ultimate state” for both dense and loose sand as previously established based on conventional drained triaxial tests is not supported by the plane-strain data. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282009%29135%3A1%2810 [...] [article] Effect of loading mode on strain softening and instability behavior of sand in plane-strain tests [texte imprimé] / J. Chu, Auteur ; D. Wanatowski, Auteur . - 2009 . - pp. 108–120. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N°1 (Janvier 2009) . - pp. 108–120 Mots-clés : Sand  Laboratory  tests  Plane  strain  Strain  softening Résumé : Experimental data to study the effect of loading mode on the strain softening and instability behavior of sand under plane-strain conditions are presented in this paper. A new plane-strain apparatus was adopted to conduct K0 consolidated drained and undrained tests under both deformation-controlled and load-controlled loading modes. The drained behavior of very loose and medium dense sand and the undrained behavior of very loose sand under plane-strain conditions were characterized. The test results show that the loading mode affects the postpeak behavior and controls whether strain softening or instability will occur in the postpeak region. Shear bands occurred in tests conducted on medium dense sand, but not in tests for very loose sand. The failure line and critical state line are not affected by the loading mode. The study also shows that the concept of a unique “ultimate state” for both dense and loose sand as previously established based on conventional drained triaxial tests is not supported by the plane-strain data. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282009%29135%3A1%2810 [...]

Factors affecting pre-failure instability of sand under plane-strain conditions / D. Wanatowski in Géotechnique, Vol. 62 N° 2 (Fevrier 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 2 (Fevrier 2012) . - pp. 121 –135 Titre : Factors affecting pre-failure instability of sand under plane-strain conditions Type de document : texte imprimé Auteurs : D. Wanatowski, Auteur ; J. Chu, Auteur Année de publication : 2012 Article en page(s) : pp. 121 –135 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Liquefaction  Sands  Laboratory  tests  Slopes  Pore  pressures  Failure Résumé : Experimental data obtained from a plane-strain apparatus are presented in this paper to show that a pre-failure instability in the form of a rapid and sustained increase in strain rate can occur for both contractive and dilative sand under fully drained conditions. However, this type of instability is different from the runaway type of instability observed under undrained conditions, and has therefore been called conditional instability. Despite the differences, the conditions for both types of instability are the same for contractive sand. There are also other factors that affect the pre-failure instability of sand observed in the laboratory. These include the stress ratio, void ratio, sand state, load control mode and reduction rate of the effective confining stress. In this paper, these factors are discussed and analysed using experimental data obtained from undrained instability (or creep) tests and constant shear drained (CSD) tests carried out under plane-strain conditions. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.P.111 [article] Factors affecting pre-failure instability of sand under plane-strain conditions [texte imprimé] / D. Wanatowski, Auteur ; J. Chu, Auteur . - 2012 . - pp. 121 –135. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 2 (Fevrier 2012) . - pp. 121 –135 Mots-clés : Liquefaction  Sands  Laboratory  tests  Slopes  Pore  pressures  Failure Résumé : Experimental data obtained from a plane-strain apparatus are presented in this paper to show that a pre-failure instability in the form of a rapid and sustained increase in strain rate can occur for both contractive and dilative sand under fully drained conditions. However, this type of instability is different from the runaway type of instability observed under undrained conditions, and has therefore been called conditional instability. Despite the differences, the conditions for both types of instability are the same for contractive sand. There are also other factors that affect the pre-failure instability of sand observed in the laboratory. These include the stress ratio, void ratio, sand state, load control mode and reduction rate of the effective confining stress. In this paper, these factors are discussed and analysed using experimental data obtained from undrained instability (or creep) tests and constant shear drained (CSD) tests carried out under plane-strain conditions. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.P.111

Instability conditions of loose sand in plane strain / J. Chu in Journal of geotechnical and geoenvironmental engineering, Vol. 134 N°1 (Janvier 2008) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 134 N°1 (Janvier 2008) . - pp. 136–142 Titre : Instability conditions of loose sand in plane strain Type de document : texte imprimé Auteurs : J. Chu, Auteur ; D. Wanatowski, Auteur Année de publication : 2008 Article en page(s) : pp. 136–142 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Laboratory  tests  Liquefaction  Sand  Stress  strain  relations Résumé : When a loose sand specimen is loaded under an undrained condition, it may become unstable. The instability conditions may be specified by an instability line determined using undrained tests. However, the instability behavior of sand has seldom been studied under plane-strain conditions. Experimental data obtained under both triaxial and plane-strain conditions are presented in this paper to define the instability conditions of loose sand under plane-strain conditions. Using the state parameter, a unified relationship can be established between the normalized slope of instability line and the state parameters for both axisymmetric and plane-strain conditions. Using this relationship, the instability conditions established under axisymmetric conditions can also be used for plane-strain conditions. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A1%2813 [...] [article] Instability conditions of loose sand in plane strain [texte imprimé] / J. Chu, Auteur ; D. Wanatowski, Auteur . - 2008 . - pp. 136–142. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 134 N°1 (Janvier 2008) . - pp. 136–142 Mots-clés : Laboratory  tests  Liquefaction  Sand  Stress  strain  relations Résumé : When a loose sand specimen is loaded under an undrained condition, it may become unstable. The instability conditions may be specified by an instability line determined using undrained tests. However, the instability behavior of sand has seldom been studied under plane-strain conditions. Experimental data obtained under both triaxial and plane-strain conditions are presented in this paper to define the instability conditions of loose sand under plane-strain conditions. Using the state parameter, a unified relationship can be established between the normalized slope of instability line and the state parameters for both axisymmetric and plane-strain conditions. Using this relationship, the instability conditions established under axisymmetric conditions can also be used for plane-strain conditions. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A1%2813 [...]

Modified state parameter for characterizing static liquefaction of sand with fines / D. C. Bobei in Canadian geotechnical journal, Vol. 46 N° 3 (Mars 2009) 

Public ISBD [article]  in Canadian geotechnical journal > Vol. 46 N° 3 (Mars 2009) . - pp. 281–295 Titre : Modified state parameter for characterizing static liquefaction of sand with fines Type de document : texte imprimé Auteurs : D. C. Bobei, Auteur ; S. R. Lo, Auteur ; D. Wanatowski, Auteur Article en page(s) : pp. 281–295 Note générale : Science de la Terre Langues : Anglais (eng) Mots-clés : Sand  with  fines  Laboratory  tests  Static  liquefaction  Critical  state  Steady  state  State  parameter  Sable  avec  fines  Essais  en  laboratoire  Liquéfaction  statique  Etat  critique  Régime  permanent  Paramètre  d’état Index. décimale : 550 Sciences auxiliaires de la géologie. Résumé : An experimental study was carried out to investigate the static liquefaction behaviour of sand with a small amount of plastic and nonplastic fines. Five series of tests were conducted in drained and undrained conditions. The drained test results indicate not only that the failure line coincides with the critical state, but also that the development of volumetric strain during shearing was not sensitive to the initial confining pressure. In both isotropically and anisotropically consolidated undrained tests, a so-called “reverse behaviour” was consistently observed. The results were also interpreted in the critical state framework. The critical and steady state (CS/SS) data were found to trace along the same curve in e–log( p′) space, irrespective of the stress history and effective stress paths. A comparison between the isotropic consolidation line (ICL) and critical state (CS) curve showed that a small amount of fines can significantly change the shape and position of the ICL relative to the CS curve. Furthermore, the soil behaviour manifested in both drained and undrained shearing led to the development of a modified state parameter. Une étude expérimentale a été effectuée pour examiner la liquéfaction statique d’un sable contenant une faible quantité de fines plastiques et non-plastiques. Cinq séries d’essais ont été faites en conditions drainées et non-drainées. Les résultats des essais en condition drainée indiquent que non seulement la ligne de rupture coïncide avec l’état critique, mais aussi que le développement de déformation volumétrique durant le cisaillement n’est pas affecté par la pression de confinement initiale. Dans les essais non-drainés consolidés isotropiquement et anisotropiquement, un comportement de type « inverse » a été observé de façon consistante. Les résultats ont aussi été interprétés dans le cadre de l’état critique. Il a été observé que les données à l’état critique et en régime permanent « CS/SS » tracent une courbe similaire dans l’espace e–log( p′), indépendamment de l’historique des contraintes et du cheminement des contraintes effectives. Une comparaison entre la courbe de la ligne de consolidation isotropique « ICL » et d’état critique « CS » démontre qu’une petite quantité de particules fines peut modifier de façon significative la forme et la position de la courbe ICL par rapport à CS. De plus, le comportement du sol en cisaillement dans des conditions drainées et non-drainées a amené au développement d’un paramètre d’état modifié. DEWEY : 550 ISSN : 0008-3674 En ligne : http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=f [...] [article] Modified state parameter for characterizing static liquefaction of sand with fines [texte imprimé] / D. C. Bobei, Auteur ; S. R. Lo, Auteur ; D. Wanatowski, Auteur . - pp. 281–295. Science de la Terre Langues : Anglais (eng) in Canadian geotechnical journal > Vol. 46 N° 3 (Mars 2009) . - pp. 281–295 Mots-clés : Sand  with  fines  Laboratory  tests  Static  liquefaction  Critical  state  Steady  state  State  parameter  Sable  avec  fines  Essais  en  laboratoire  Liquéfaction  statique  Etat  critique  Régime  permanent  Paramètre  d’état Index. décimale : 550 Sciences auxiliaires de la géologie. Résumé : An experimental study was carried out to investigate the static liquefaction behaviour of sand with a small amount of plastic and nonplastic fines. Five series of tests were conducted in drained and undrained conditions. The drained test results indicate not only that the failure line coincides with the critical state, but also that the development of volumetric strain during shearing was not sensitive to the initial confining pressure. In both isotropically and anisotropically consolidated undrained tests, a so-called “reverse behaviour” was consistently observed. The results were also interpreted in the critical state framework. The critical and steady state (CS/SS) data were found to trace along the same curve in e–log( p′) space, irrespective of the stress history and effective stress paths. A comparison between the isotropic consolidation line (ICL) and critical state (CS) curve showed that a small amount of fines can significantly change the shape and position of the ICL relative to the CS curve. Furthermore, the soil behaviour manifested in both drained and undrained shearing led to the development of a modified state parameter. Une étude expérimentale a été effectuée pour examiner la liquéfaction statique d’un sable contenant une faible quantité de fines plastiques et non-plastiques. Cinq séries d’essais ont été faites en conditions drainées et non-drainées. Les résultats des essais en condition drainée indiquent que non seulement la ligne de rupture coïncide avec l’état critique, mais aussi que le développement de déformation volumétrique durant le cisaillement n’est pas affecté par la pression de confinement initiale. Dans les essais non-drainés consolidés isotropiquement et anisotropiquement, un comportement de type « inverse » a été observé de façon consistante. Les résultats ont aussi été interprétés dans le cadre de l’état critique. Il a été observé que les données à l’état critique et en régime permanent « CS/SS » tracent une courbe similaire dans l’espace e–log( p′), indépendamment de l’historique des contraintes et du cheminement des contraintes effectives. Une comparaison entre la courbe de la ligne de consolidation isotropique « ICL » et d’état critique « CS » démontre qu’une petite quantité de particules fines peut modifier de façon significative la forme et la position de la courbe ICL par rapport à CS. De plus, le comportement du sol en cisaillement dans des conditions drainées et non-drainées a amené au développement d’un paramètre d’état modifié. DEWEY : 550 ISSN : 0008-3674 En ligne : http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=f [...]