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Détail de l'auteur
Auteur C. F. Leung
Documents disponibles écrits par cet auteur
Affiner la rechercheBehavior of pile groups subject to excavation-induced soil movement in very soft clay / D. E. L. Ong in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 10 (Octobre 2009)
in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 10 (Octobre 2009) . - pp. 1462–1474
Titre : Behavior of pile groups subject to excavation-induced soil movement in very soft clay Type de document : texte imprimé Auteurs : D. E. L. Ong, Auteur ; C. F. Leung, Auteur ; Y. K. Chow, Auteur Année de publication : 2009 Article en page(s) : pp. 1462–1474 Note générale : Géotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Pile groupsBendingCentrifuge modelsClaysDeflectionExcavationRetaining wallsSoil pressure Résumé : A series of centrifuge model tests was conducted to investigate the behavior of pile groups of various sizes and configurations behind a retaining wall in very soft clay. With a 1.2-m excavation in front of the wall, which may simulate the initial stage of an excavation prior to strutting, the test results reveal that the induced bending moment on an individual pile in a free-head pile group is always smaller than that on a corresponding single pile located at the same distance behind the wall. This is attributed to the shadowing and reinforcing effects of other piles within the group. The degree of shadowing experienced by a pile depends on its relative position in the pile group. With a capped-head pile group, the individual piles are forced to interact in unison though subjected to different magnitudes of soil movement. Thus, despite being subjected to a larger soil movement, the induced bending moment on the front piles is moderated by the rear piles through the pile cap. A finite element program developed at the National University of Singapore is employed to back-analyze the centrifuge test data. The program gives a reasonably good prediction of the induced pile bending moments provided an appropriate modification factor is applied for the free-field soil movement and the amount of restraint provided by the pile cap is properly accounted for. The modification factor applied to the free-field soil movement accounts the reinforcing effect of the piles on the soil movement. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000095 [article] Behavior of pile groups subject to excavation-induced soil movement in very soft clay [texte imprimé] / D. E. L. Ong, Auteur ; C. F. Leung, Auteur ; Y. K. Chow, Auteur . - 2009 . - pp. 1462–1474.
Géotechnical and geoenvironmental engineering
Langues : Anglais (eng)
in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 10 (Octobre 2009) . - pp. 1462–1474
Mots-clés : Pile groupsBendingCentrifuge modelsClaysDeflectionExcavationRetaining wallsSoil pressure Résumé : A series of centrifuge model tests was conducted to investigate the behavior of pile groups of various sizes and configurations behind a retaining wall in very soft clay. With a 1.2-m excavation in front of the wall, which may simulate the initial stage of an excavation prior to strutting, the test results reveal that the induced bending moment on an individual pile in a free-head pile group is always smaller than that on a corresponding single pile located at the same distance behind the wall. This is attributed to the shadowing and reinforcing effects of other piles within the group. The degree of shadowing experienced by a pile depends on its relative position in the pile group. With a capped-head pile group, the individual piles are forced to interact in unison though subjected to different magnitudes of soil movement. Thus, despite being subjected to a larger soil movement, the induced bending moment on the front piles is moderated by the rear piles through the pile cap. A finite element program developed at the National University of Singapore is employed to back-analyze the centrifuge test data. The program gives a reasonably good prediction of the induced pile bending moments provided an appropriate modification factor is applied for the free-field soil movement and the amount of restraint provided by the pile cap is properly accounted for. The modification factor applied to the free-field soil movement accounts the reinforcing effect of the piles on the soil movement. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000095
in Canadian geotechnical journal > Vol. 46 N° 1 (Janvier 2009) . - pp. 10–24
Titre : Centrifuge and numerical modeling of axial load effects on piles in consolidating ground Type de document : texte imprimé Auteurs : S. Y. Lam, Auteur ; Charles W.W. Ng, Auteur ; C. F. Leung, Auteur Article en page(s) : pp. 10–24 Note générale : Sciences de la Terre Langues : Anglais (eng) Mots-clés : Centrifuge Numerical Downdrag Dragload Pile groups Negative skin friction Centrifuge Numérique Entraînement vers le bas Groupes de pieux Frottement superficiel négatif Index. décimale : 550 Sciences auxiliaires de la géologie. Résumé : This paper reports the results of four centrifuge model tests that were undertaken to investigate behavior of floating piles subjected to negative skin friction (NSF) and to study effects of axial load on the load-transfer mechanism along single floating piles and shielded center piles inside a group of sacrificing piles. In addition, three-dimensional numerical analyses of the centrifuge model tests were carried out with elasto-plastic slip considered at the pile–soil interface. Prior to applying load, the measured neutral plane position of the single floating piles was located at approximately the three-quarter depth level of the embedded pile length. The neutral plane elevation shifts lower down the pile shaft as the distance of pile tip above the bearing stratum decreases. Under the application of axial load, the dragload generated by excessive soil settlement decreases and is eventually eliminated. The amount of axial load for complete NSF elimination does not seem to be significantly affected by the presence of sacrificing piles, but it does increase with end-bearing stiffness of the pile. Numerical simulation revealed that the hang-up effect is not altered by the application of axial load.
Cet article présente les résultats de quatre essais sur modèle au centrifuge qui ont été réalisés pour étudier le comportement de pieux flottants assujettis au frottement superficiel négatif (« NSF ») et pour étudier aussi les effets de la charge axiale sur le mécanisme de transfert le long de pieux simples flottants et d’un pieu central protégé dans un groupe de pieux écran. De plus, on a réalisé des analyses numériques à trois dimensions des essais sur modèle au centrifuge en considérant un glissement élasto-plastique à l’interface pieu–sol. Avant d’appliquer la charge, la position mesurée du plan neutre des pieux simples flottants était localisée à une profondeur d’environ trois quarts de la longueur enfouie du pieu. L’élévation du plan neutre se déplace vers le bas du fût du pieu à mesure que la distance de la pointe du pieu au-dessus de la couche portante décroît. Sous l’application de la charge axiale, la charge d’entraînement générée par le tassement excessif du sol diminue et est éliminée éventuellement. La quantité de charge axiale requise pour l’élimination complète du « NSF » ne semble pas être affectée appréciablement par la présence des pieux écran, mais elle s’accroît avec la rigidité de la pointe portante du pieu. Une simulation numérique révèle que l’effet de suspension du pieu n’est pas altéré par l’application de la charge axiale.
DEWEY : 550 ISSN : 0008-3674 En ligne : http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=f [...] [article] Centrifuge and numerical modeling of axial load effects on piles in consolidating ground [texte imprimé] / S. Y. Lam, Auteur ; Charles W.W. Ng, Auteur ; C. F. Leung, Auteur . - pp. 10–24.
Sciences de la Terre
Langues : Anglais (eng)
in Canadian geotechnical journal > Vol. 46 N° 1 (Janvier 2009) . - pp. 10–24
Mots-clés : Centrifuge Numerical Downdrag Dragload Pile groups Negative skin friction Centrifuge Numérique Entraînement vers le bas Groupes de pieux Frottement superficiel négatif Index. décimale : 550 Sciences auxiliaires de la géologie. Résumé : This paper reports the results of four centrifuge model tests that were undertaken to investigate behavior of floating piles subjected to negative skin friction (NSF) and to study effects of axial load on the load-transfer mechanism along single floating piles and shielded center piles inside a group of sacrificing piles. In addition, three-dimensional numerical analyses of the centrifuge model tests were carried out with elasto-plastic slip considered at the pile–soil interface. Prior to applying load, the measured neutral plane position of the single floating piles was located at approximately the three-quarter depth level of the embedded pile length. The neutral plane elevation shifts lower down the pile shaft as the distance of pile tip above the bearing stratum decreases. Under the application of axial load, the dragload generated by excessive soil settlement decreases and is eventually eliminated. The amount of axial load for complete NSF elimination does not seem to be significantly affected by the presence of sacrificing piles, but it does increase with end-bearing stiffness of the pile. Numerical simulation revealed that the hang-up effect is not altered by the application of axial load.
Cet article présente les résultats de quatre essais sur modèle au centrifuge qui ont été réalisés pour étudier le comportement de pieux flottants assujettis au frottement superficiel négatif (« NSF ») et pour étudier aussi les effets de la charge axiale sur le mécanisme de transfert le long de pieux simples flottants et d’un pieu central protégé dans un groupe de pieux écran. De plus, on a réalisé des analyses numériques à trois dimensions des essais sur modèle au centrifuge en considérant un glissement élasto-plastique à l’interface pieu–sol. Avant d’appliquer la charge, la position mesurée du plan neutre des pieux simples flottants était localisée à une profondeur d’environ trois quarts de la longueur enfouie du pieu. L’élévation du plan neutre se déplace vers le bas du fût du pieu à mesure que la distance de la pointe du pieu au-dessus de la couche portante décroît. Sous l’application de la charge axiale, la charge d’entraînement générée par le tassement excessif du sol diminue et est éliminée éventuellement. La quantité de charge axiale requise pour l’élimination complète du « NSF » ne semble pas être affectée appréciablement par la présence des pieux écran, mais elle s’accroît avec la rigidité de la pointe portante du pieu. Une simulation numérique révèle que l’effet de suspension du pieu n’est pas altéré par l’application de la charge axiale.
DEWEY : 550 ISSN : 0008-3674 En ligne : http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=f [...]
in Géotechnique > Vol. 60 N° 11 (Novembre 2010) . - pp. 825–842
Titre : Centrifuge model study of spudcan penetration in sand overlying clay Type de document : texte imprimé Auteurs : K. L. Teh, Auteur ; C. F. Leung, Auteur ; Y. K. Chow, Auteur Année de publication : 2011 Article en page(s) : pp. 825–842 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Bearing capacity Sands Footings/foundations Centrifuge modelling Clays Offshore engineering Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : A series of centrifuge model tests has been conducted to investigate the bearing resistance of spudcan foundations of offshore jack-up rigs in sand overlying normally consolidated clay. The spudcan bearing-resistance profiles measured in most of the tests recorded a peak resistance at a shallow depth within the upper sand layer, followed by an abrupt post-peak reduction in resistance causing the spudcan to plunge into the underlying soft clay. This phenomenon is commonly termed as ‘spudcan punch-through hazard', which potentially leads to severe structural damage of jack-up rigs in the field. The centrifuge test results revealed that the ratio of upper sand layer thickness over spudcan diameter and the ratio of bearing resistance between the upper sand and underlying clay affect the development of spudcan bearing resistance. The limitations of existing design methods, which were derived for the ultimate bearing capacity of pre-embedded shallow foundation to assess the spudcan bearing resistance-depth profile, are also identified. It is proposed that the profile may be assessed by focusing on three key characteristic bearing resistances.
DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.077 [article] Centrifuge model study of spudcan penetration in sand overlying clay [texte imprimé] / K. L. Teh, Auteur ; C. F. Leung, Auteur ; Y. K. Chow, Auteur . - 2011 . - pp. 825–842.
Génie Civil
Langues : Anglais (eng)
in Géotechnique > Vol. 60 N° 11 (Novembre 2010) . - pp. 825–842
Mots-clés : Bearing capacity Sands Footings/foundations Centrifuge modelling Clays Offshore engineering Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : A series of centrifuge model tests has been conducted to investigate the bearing resistance of spudcan foundations of offshore jack-up rigs in sand overlying normally consolidated clay. The spudcan bearing-resistance profiles measured in most of the tests recorded a peak resistance at a shallow depth within the upper sand layer, followed by an abrupt post-peak reduction in resistance causing the spudcan to plunge into the underlying soft clay. This phenomenon is commonly termed as ‘spudcan punch-through hazard', which potentially leads to severe structural damage of jack-up rigs in the field. The centrifuge test results revealed that the ratio of upper sand layer thickness over spudcan diameter and the ratio of bearing resistance between the upper sand and underlying clay affect the development of spudcan bearing resistance. The limitations of existing design methods, which were derived for the ultimate bearing capacity of pre-embedded shallow foundation to assess the spudcan bearing resistance-depth profile, are also identified. It is proposed that the profile may be assessed by focusing on three key characteristic bearing resistances.
DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.077
in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 799 –810
Titre : Centrifuge modelling of spudcan–pile interaction in soft clay Type de document : texte imprimé Auteurs : Y. Xie, Auteur ; C. F. Leung, Auteur ; Y. K. Chow, Auteur Année de publication : 2012 Article en page(s) : pp. 799 –810 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Soil/structure interaction Clays Piles Offshore engineering Footings/foundations Centrifuge modelling Résumé : The installation and extraction of jack-up spudcans may induce significant stresses in the adjacent piles supporting the permanent jacket platforms at an offshore site. In the present study, centrifuge model tests were conducted to investigate the effects of spudcan movements on the lateral and axial behaviour of adjacent fixed-head piles embedded in soft clay. Parameters such as jack-up operation period, clearance between the spudcan and pile, and the embedment length of the pile are examined. The test results show that the most critical period for platform piles is at the end of spudcan installation, and the lateral pile behaviour is more severely affected than the axial pile behaviour. During spudcan installation, the induced bending moment on a pile located one-quarter spudcan diameter away from the spudcan edge is about 2·4 times that of a pile located one spudcan diameter away. For a deeply buried spudcan with penetration of over three-quarters spudcan diameter, the induced bending moment on longer piles is much smaller than that on shorter piles. The experimental findings provide further insights into the underlying mechanisms governing spudcan–pile interaction in soft clay under various configurations and conditions. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.003 [article] Centrifuge modelling of spudcan–pile interaction in soft clay [texte imprimé] / Y. Xie, Auteur ; C. F. Leung, Auteur ; Y. K. Chow, Auteur . - 2012 . - pp. 799 –810.
Génie Civil
Langues : Anglais (eng)
in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 799 –810
Mots-clés : Soil/structure interaction Clays Piles Offshore engineering Footings/foundations Centrifuge modelling Résumé : The installation and extraction of jack-up spudcans may induce significant stresses in the adjacent piles supporting the permanent jacket platforms at an offshore site. In the present study, centrifuge model tests were conducted to investigate the effects of spudcan movements on the lateral and axial behaviour of adjacent fixed-head piles embedded in soft clay. Parameters such as jack-up operation period, clearance between the spudcan and pile, and the embedment length of the pile are examined. The test results show that the most critical period for platform piles is at the end of spudcan installation, and the lateral pile behaviour is more severely affected than the axial pile behaviour. During spudcan installation, the induced bending moment on a pile located one-quarter spudcan diameter away from the spudcan edge is about 2·4 times that of a pile located one spudcan diameter away. For a deeply buried spudcan with penetration of over three-quarters spudcan diameter, the induced bending moment on longer piles is much smaller than that on shorter piles. The experimental findings provide further insights into the underlying mechanisms governing spudcan–pile interaction in soft clay under various configurations and conditions. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.003
in Géotechnique > Vol. 62 N° 5 (Mai 2012) . - pp. 401 –413
Titre : Effect of time on spudcan–footprint interaction in clay Type de document : texte imprimé Auteurs : C.T. Gan, Auteur ; C. F. Leung, Auteur ; M. J. Cassidy, Auteur Année de publication : 2012 Article en page(s) : pp. 401 –413 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Centrifuge modelling Clays Soil/structure interaction Foundations Offshore engineering Résumé : Mobile drilling platforms often return to sites where previous installation, operation and extraction have formed footprints on the seabed. Owing to soil consolidation during the jack-up operational period and the intervening period before reinstallation, the interaction between a new spudcan installation and an existing footprint is complex and time dependent. This paper presents a series of drum centrifuge model tests to investigate the changes in the shear strength of soils beneath and adjacent to a spudcan footprint in normally and overconsolidated clays. The changes with time after two different jack-up operational periods are presented. The results reveal that the soil beneath a footprint generally loses some strength initially, owing to soil remoulding, but it subsequently regains its strength with time as it reconsolidates. The soil remoulding and subsequent strength gain are found to be more significant in normally consolidated clay than in overconsolidated clay. A longer jack-up operational period has an effect of strengthening the underlying soil below the spudcan in both clays. The vertical load, induced horizontal load and moment on a spudcan during its reinstallation into an existing footprint at different times after footprint formation are studied. Compared with the load for installing a spudcan for the first time, the load required to reinstall the same spudcan to the same depth is smaller in normally consolidated clay if the elapsed time between footprint formation and spudcan reinstallation is relatively short. The required load for spudcan reinstallation subsequently increases with footprint elapsed time. For overconsolidated clay, the load required for spudcan reinstallation is always smaller than that for initial spudcan installation, irrespective of the time between installations. The effects of original in situ soil strength, changes in soil strength with time and footprint elapsed time on the interaction between spudcan and footprint are examined. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.P.063 [article] Effect of time on spudcan–footprint interaction in clay [texte imprimé] / C.T. Gan, Auteur ; C. F. Leung, Auteur ; M. J. Cassidy, Auteur . - 2012 . - pp. 401 –413.
Génie Civil
Langues : Anglais (eng)
in Géotechnique > Vol. 62 N° 5 (Mai 2012) . - pp. 401 –413
Mots-clés : Centrifuge modelling Clays Soil/structure interaction Foundations Offshore engineering Résumé : Mobile drilling platforms often return to sites where previous installation, operation and extraction have formed footprints on the seabed. Owing to soil consolidation during the jack-up operational period and the intervening period before reinstallation, the interaction between a new spudcan installation and an existing footprint is complex and time dependent. This paper presents a series of drum centrifuge model tests to investigate the changes in the shear strength of soils beneath and adjacent to a spudcan footprint in normally and overconsolidated clays. The changes with time after two different jack-up operational periods are presented. The results reveal that the soil beneath a footprint generally loses some strength initially, owing to soil remoulding, but it subsequently regains its strength with time as it reconsolidates. The soil remoulding and subsequent strength gain are found to be more significant in normally consolidated clay than in overconsolidated clay. A longer jack-up operational period has an effect of strengthening the underlying soil below the spudcan in both clays. The vertical load, induced horizontal load and moment on a spudcan during its reinstallation into an existing footprint at different times after footprint formation are studied. Compared with the load for installing a spudcan for the first time, the load required to reinstall the same spudcan to the same depth is smaller in normally consolidated clay if the elapsed time between footprint formation and spudcan reinstallation is relatively short. The required load for spudcan reinstallation subsequently increases with footprint elapsed time. For overconsolidated clay, the load required for spudcan reinstallation is always smaller than that for initial spudcan installation, irrespective of the time between installations. The effects of original in situ soil strength, changes in soil strength with time and footprint elapsed time on the interaction between spudcan and footprint are examined. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.P.063
