Documents disponibles écrits par cet auteur

Collapse of loose sand with the addition of fines / J. Yang in Géotechnique, Vol. 62 N° 12 (Décembre 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 12 (Décembre 2012) . - pp. 1111 –1125 Titre : Collapse of loose sand with the addition of fines : The role of particle shape Type de document : texte imprimé Auteurs : J. Yang, Auteur ; L. M. Wei, Auteur Année de publication : 2012 Article en page(s) : pp. 1111 –1125 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Laboratory  tests  Silts  Fabric/structure  of  soils  Sands  Shear  strength  Liquefaction Résumé : This paper describes a fundamental study to explore the role of particle shape in the shear behaviour of mixtures of sand and fine particles (fines) through macro-scale and grain-scale laboratory experiments together with interpretations in the framework of critical state soil mechanics and conceptual micromechanics models. Two non-plastic fines of distinct shape (angular crushed silica fines and rounded glass beads) were added to two uniform quartz sands (Toyoura sand and Fujian sand) to produce four binary mixtures. Laboratory quantification of particle shape and size was conducted for both fines and sands, and a series of undrained triaxial tests was performed to investigate the overall response of the mixed soils at different percentages of fines. One of the significant findings is that the critical state friction angle of a mixed soil is affected not only by the shape of coarse particles but also by the shape of fine particles, and this shape effect is coupled with fines content. When a small amount of crushed silica fines was added to either Toyoura sand or Fujian sand, the critical state friction angle increased slightly with fines content; however, when a small amount of glass beads was added to either sand, the critical state friction angle decreased markedly with an increase in fines content. A new index, termed combined roundness, is proposed to account for the coupled effects of particle shape and fines content. The study also provides evidence showing that the undrained shear behaviour and collapsibility of a mixed soil are closely related to the shape of its constituent particles: a mixed soil containing rounded fines tends to exhibit higher susceptibility to collapse than a mixed soil containing angular fines of the same percentage, and this tendency will become more evident if the base sand is also composed of rounded particles. In addition, the study provides the first experimental evidence showing that the quasi-steady state marks a transition from a metastable to a stable microstructure. It is postulated that in a binary mixture composed of fine and coarse particles that are both rounded, the particles favour rolling, thus yielding a microstructure that is unstable, whereas in a binary mixture composed of fine and coarse particles that are both angular, the particles favour sliding rather than rolling, thus leading to a much more stable structure and response. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.11.P.062 [article] Collapse of loose sand with the addition of fines : The role of particle shape [texte imprimé] / J. Yang, Auteur ; L. M. Wei, Auteur . - 2012 . - pp. 1111 –1125. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 12 (Décembre 2012) . - pp. 1111 –1125 Mots-clés : Laboratory  tests  Silts  Fabric/structure  of  soils  Sands  Shear  strength  Liquefaction Résumé : This paper describes a fundamental study to explore the role of particle shape in the shear behaviour of mixtures of sand and fine particles (fines) through macro-scale and grain-scale laboratory experiments together with interpretations in the framework of critical state soil mechanics and conceptual micromechanics models. Two non-plastic fines of distinct shape (angular crushed silica fines and rounded glass beads) were added to two uniform quartz sands (Toyoura sand and Fujian sand) to produce four binary mixtures. Laboratory quantification of particle shape and size was conducted for both fines and sands, and a series of undrained triaxial tests was performed to investigate the overall response of the mixed soils at different percentages of fines. One of the significant findings is that the critical state friction angle of a mixed soil is affected not only by the shape of coarse particles but also by the shape of fine particles, and this shape effect is coupled with fines content. When a small amount of crushed silica fines was added to either Toyoura sand or Fujian sand, the critical state friction angle increased slightly with fines content; however, when a small amount of glass beads was added to either sand, the critical state friction angle decreased markedly with an increase in fines content. A new index, termed combined roundness, is proposed to account for the coupled effects of particle shape and fines content. The study also provides evidence showing that the undrained shear behaviour and collapsibility of a mixed soil are closely related to the shape of its constituent particles: a mixed soil containing rounded fines tends to exhibit higher susceptibility to collapse than a mixed soil containing angular fines of the same percentage, and this tendency will become more evident if the base sand is also composed of rounded particles. In addition, the study provides the first experimental evidence showing that the quasi-steady state marks a transition from a metastable to a stable microstructure. It is postulated that in a binary mixture composed of fine and coarse particles that are both rounded, the particles favour rolling, thus yielding a microstructure that is unstable, whereas in a binary mixture composed of fine and coarse particles that are both angular, the particles favour sliding rather than rolling, thus leading to a much more stable structure and response. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.11.P.062

Cyclic behaviour and resistance of saturated sand under non-symmetrical loading / J. Yang in Géotechnique, Vol. LXI N° 1 (Janvier 2011) 

Public ISBD [article]  in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 59–73 Titre : Cyclic behaviour and resistance of saturated sand under non-symmetrical loading Type de document : texte imprimé Auteurs : J. Yang, Auteur ; H. Y. Sze, Auteur Année de publication : 2011 Article en page(s) : pp. 59–73 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Shear  strength  Earthquakes  Liquefaction  Laboratory  tests  Failure  Sands Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper reports findings from an experimental study that aimed to investigate the undrained behaviour of sand in non-symmetrical cyclic loading, and to clarify the role of initial static shear in liquefaction resistance. The testing programme, conducted on a standard sand under triaxial conditions, covers a broad range of initial states in terms of relative density, confining stress and initial shear stress ratio (α). Three distinct failure modes have been identified from the tests: flow-type failure, cyclic mobility and plastic strain accumulation. Of these, flow-type failure, characterised by abrupt runaway deformations without any prior warning, is the most critical, and pertains to sand in the loose state. The tests also demonstrate that the presence of initial static shear stress is beneficial to the liquefaction resistance of loose sand at low α levels, but it becomes detrimental at high α levels. In this connection the concept of threshold α is proposed, together with the use of a no-stress-reversal line for better characterisation of the effect of initial static shear. Furthermore, in the conceptual framework of critical state soil mechanics, a fairly good linear relationship has been established between the threshold α and the state parameter ψ that collectively accounts for the initial relative density and mean stress level. This relationship suggests that the threshold α decreases with increasing values of ψ , or with sand becoming looser than the critical state. It is further proposed that the concept of threshold α also applies to sand at high relative density, as long as the confining stress becomes sufficiently high. This proposal leads to a unified and consistent interpretation of the complicated static shear effect. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.019 [article] Cyclic behaviour and resistance of saturated sand under non-symmetrical loading [texte imprimé] / J. Yang, Auteur ; H. Y. Sze, Auteur . - 2011 . - pp. 59–73. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 59–73 Mots-clés : Shear  strength  Earthquakes  Liquefaction  Laboratory  tests  Failure  Sands Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper reports findings from an experimental study that aimed to investigate the undrained behaviour of sand in non-symmetrical cyclic loading, and to clarify the role of initial static shear in liquefaction resistance. The testing programme, conducted on a standard sand under triaxial conditions, covers a broad range of initial states in terms of relative density, confining stress and initial shear stress ratio (α). Three distinct failure modes have been identified from the tests: flow-type failure, cyclic mobility and plastic strain accumulation. Of these, flow-type failure, characterised by abrupt runaway deformations without any prior warning, is the most critical, and pertains to sand in the loose state. The tests also demonstrate that the presence of initial static shear stress is beneficial to the liquefaction resistance of loose sand at low α levels, but it becomes detrimental at high α levels. In this connection the concept of threshold α is proposed, together with the use of a no-stress-reversal line for better characterisation of the effect of initial static shear. Furthermore, in the conceptual framework of critical state soil mechanics, a fairly good linear relationship has been established between the threshold α and the state parameter ψ that collectively accounts for the initial relative density and mean stress level. This relationship suggests that the threshold α decreases with increasing values of ψ , or with sand becoming looser than the critical state. It is further proposed that the concept of threshold α also applies to sand at high relative density, as long as the confining stress becomes sufficiently high. This proposal leads to a unified and consistent interpretation of the complicated static shear effect. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.019

Cyclic strength of sand under sustained shear stress / J. Yang in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 12 (Décembre 2011) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1275-1285 Titre : Cyclic strength of sand under sustained shear stress Type de document : texte imprimé Auteurs : J. Yang, Auteur ; H. Y. Sze, Auteur Année de publication : 2012 Article en page(s) : pp. 1275-1285 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Critical  state  Cyclic  strength  Failure  Laboratory  tests  Liquefaction  Sands Résumé : The existence of initial shear stress can have a significant effect on the cyclic strength or liquefaction potential of sand. This effect is not yet fully understood because of a lack of convergence and consistency in the existing data and interpretations, leading to great uncertainty in quantifying the effect for practical applications. This paper presents new experimental results on a silica sand to validate the concept known as threshold α, below which the cyclic strength of sand increases with α and above which the cyclic strength decreases with α (with α representing the sustained shear stress level). On the basis of a series of monotonic loading tests on the same sand, and in the framework of critical state soil mechanics, it is further confirmed that threshold α can be well related to a state parameter in the void ratio-mean effective stress plane and thereby a unified and consistent interpretation can be established. A new platform is proposed on which the relationship between cyclic strength and state parameter is represented by a linear line, and this line will rotate clockwise as α increases. This platform provides an effective analytical tool for the study of the effect of sustained shear stress on the cyclic strength of sand. Moreover, the study also shows that the cyclic loading path is well linked with the monotonic loading path under different sustained shear stress levels, and this correspondence sheds light on the mechanisms underlying a variety of experimental observations. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i12/p1275_s1?isAuthorized=no [article] Cyclic strength of sand under sustained shear stress [texte imprimé] / J. Yang, Auteur ; H. Y. Sze, Auteur . - 2012 . - pp. 1275-1285. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1275-1285 Mots-clés : Critical  state  Cyclic  strength  Failure  Laboratory  tests  Liquefaction  Sands Résumé : The existence of initial shear stress can have a significant effect on the cyclic strength or liquefaction potential of sand. This effect is not yet fully understood because of a lack of convergence and consistency in the existing data and interpretations, leading to great uncertainty in quantifying the effect for practical applications. This paper presents new experimental results on a silica sand to validate the concept known as threshold α, below which the cyclic strength of sand increases with α and above which the cyclic strength decreases with α (with α representing the sustained shear stress level). On the basis of a series of monotonic loading tests on the same sand, and in the framework of critical state soil mechanics, it is further confirmed that threshold α can be well related to a state parameter in the void ratio-mean effective stress plane and thereby a unified and consistent interpretation can be established. A new platform is proposed on which the relationship between cyclic strength and state parameter is represented by a linear line, and this line will rotate clockwise as α increases. This platform provides an effective analytical tool for the study of the effect of sustained shear stress on the cyclic strength of sand. Moreover, the study also shows that the cyclic loading path is well linked with the monotonic loading path under different sustained shear stress levels, and this correspondence sheds light on the mechanisms underlying a variety of experimental observations. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i12/p1275_s1?isAuthorized=no

Is the quasi-steady state a real behaviour? / J. Yang in Géotechnique, Vol. 61 N° 2 (Fevrier 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 2 (Fevrier 2011) . - pp. 175–183 Titre : Is the quasi-steady state a real behaviour? : a micromechanical perspective Type de document : texte imprimé Auteurs : J. Yang, Auteur ; B. B. Dai, Auteur Année de publication : 2011 Article en page(s) : pp. 175–183 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Fabric/Structure  of  soils  Sands  Constitutive  relations Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Whether the so-called quasi-steady state is a real material response is a fundamental yet controversial question in the study of undrained shear behaviour of sand. An attempt is made here to clarify the question from a micromechanical viewpoint by means of a grain-scale modelling technique combined with statistical analyses. The study shows that the quasi-steady state is a real behaviour rather than a test-induced phenomenon; it is a transition state, and can be regarded as the result of spatial rearrangement of discrete particles sheared under the constant-volume condition. The quasi-steady state has distinct features that make it different from the steady state at both the macro scale and micro scale. During the loading process, the average number of contacts per particle decreases with strain until the quasi-steady state emerges, and after that it increases gradually to an approximately constant value at large deformations associated with the steady state. This result suggests that the loss of contacts is most pronounced at the quasi-steady state. The study also shows that the contact normal forces and particle rotations play a major role in the deformation process, whereas the contributions of contact tangential forces and particle sliding appear to be minor. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.129 [article] Is the quasi-steady state a real behaviour? : a micromechanical perspective [texte imprimé] / J. Yang, Auteur ; B. B. Dai, Auteur . - 2011 . - pp. 175–183. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 2 (Fevrier 2011) . - pp. 175–183 Mots-clés : Fabric/Structure  of  soils  Sands  Constitutive  relations Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Whether the so-called quasi-steady state is a real material response is a fundamental yet controversial question in the study of undrained shear behaviour of sand. An attempt is made here to clarify the question from a micromechanical viewpoint by means of a grain-scale modelling technique combined with statistical analyses. The study shows that the quasi-steady state is a real behaviour rather than a test-induced phenomenon; it is a transition state, and can be regarded as the result of spatial rearrangement of discrete particles sheared under the constant-volume condition. The quasi-steady state has distinct features that make it different from the steady state at both the macro scale and micro scale. During the loading process, the average number of contacts per particle decreases with strain until the quasi-steady state emerges, and after that it increases gradually to an approximately constant value at large deformations associated with the steady state. This result suggests that the loss of contacts is most pronounced at the quasi-steady state. The study also shows that the contact normal forces and particle rotations play a major role in the deformation process, whereas the contributions of contact tangential forces and particle sliding appear to be minor. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.129

Relating the maximum radial stress on pile shaft to pile base resistance / J. Yang in Géotechnique, Vol. 61 N° 12 (Décembre 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 12 (Décembre 2011) . - pp. 1087–1092 Titre : Relating the maximum radial stress on pile shaft to pile base resistance Type de document : texte imprimé Auteurs : J. Yang, Auteur ; F. Mu, Auteur Année de publication : 2012 Article en page(s) : pp. 1087–1092 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Piles  Bearing  capacity  Sands  stiffness  Compressibility Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : An approximate analytic relationship is developed between the maximum radial stress on the shaft of a displacement pile in sand and the base resistance of the pile. Using the cavity expansion analogy, together with a confined failure mechanism, the ratio between the two quantities, defined as a factor S t, is established as a function of the friction angle, shear stiffness, compressibility and mean effective stress of the sand near the pile tip. It is shown that, given otherwise identical input parameters, the value of S t will decrease with increasing friction angle, and with decreasing mean stress level. It also tends to decrease with an increase in relative density. It is predicted that S t has typical values between 0·03 and 0·05, in broad agreement with the range of empirically derived values in the literature. The relationship also predicts that S t may take much higher values (∼0·1) for piles installed in dense sand or in highly compressible sand. Because of the analytical nature, the established relationship provides useful insights into the mechanisms involved and important implications for design practice. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.t.006 [article] Relating the maximum radial stress on pile shaft to pile base resistance [texte imprimé] / J. Yang, Auteur ; F. Mu, Auteur . - 2012 . - pp. 1087–1092. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 12 (Décembre 2011) . - pp. 1087–1092 Mots-clés : Piles  Bearing  capacity  Sands  stiffness  Compressibility Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : An approximate analytic relationship is developed between the maximum radial stress on the shaft of a displacement pile in sand and the base resistance of the pile. Using the cavity expansion analogy, together with a confined failure mechanism, the ratio between the two quantities, defined as a factor S t, is established as a function of the friction angle, shear stiffness, compressibility and mean effective stress of the sand near the pile tip. It is shown that, given otherwise identical input parameters, the value of S t will decrease with increasing friction angle, and with decreasing mean stress level. It also tends to decrease with an increase in relative density. It is predicted that S t has typical values between 0·03 and 0·05, in broad agreement with the range of empirically derived values in the literature. The relationship also predicts that S t may take much higher values (∼0·1) for piles installed in dense sand or in highly compressible sand. Because of the analytical nature, the established relationship provides useful insights into the mechanisms involved and important implications for design practice. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.t.006

Three-dimensional noncoaxial plasticity modeling of shear band formation in geomaterials / J. G. Qian in Journal of engineering mechanics, Vol. 134 N°4 (Avril 2008) 

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Use of state-dependent strength in estimating end bearing capacity of piles in sand / J. Yang in Journal of geotechnical and geoenvironmental engineering, Vol. 134 N°7 (Juillet 2008) 

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Using direct simulation Monte Carlo with improved boundary conditions for heat and mass transfer in microchannels / J. Yang in Journal of heat transfer, Vol. 132 N° 4 (n° spécial) (Avril 2010) 

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