Documents disponibles écrits par cet auteur

Capacity of grillage foundations under horizontal loading / J. A. Knappett in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 811 –823 Titre : Capacity of grillage foundations under horizontal loading Type de document : texte imprimé Auteurs : J. A. Knappett, Auteur ; M. J. Brown, Auteur ; M. F. Bransby, Auteur Année de publication : 2012 Article en page(s) : pp. 811 –823 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Sands  Footings/foundations  Offshore  engineering  Plasticity  Model  tests Résumé : Grillage foundations are an alternative to solid surface mudmats for supporting seabed infrastructure, offering improved hydrodynamic performance and savings in foundation material. Recent research has demonstrated that grillages can be designed to have similar vertical bearing capacity to a mudmat with the same footprint. This is extended herein by: (a) determining grillage performance under horizontal loading at constant vertical load (V-H); (b) the application and development of existing plasticity-based models for predicting performance; (c) comparing the V-H behaviour with surface mudmats; and (d) discussing the implications for design. Experimental tests were conducted in sands over a range of densities and in two different modes, representing different installation procedures. In over-penetrated tests, the foundations were installed to achieve a vertical bearing capacity V 0, followed by horizontal loading at a constant vertical load with V < V 0. In normally penetrated tests, foundations were installed to V 0 before horizontal loading at constant vertical load with V = V 0. Both normalised V-H yield surfaces and a plasticity-based simulation model are presented for use in design. Laboratory-scale grillages offer improved horizontal capacity in loose and medium-dense sands and similar horizontal capacity in very dense sand, compared with surface mudmats. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.012 [article] Capacity of grillage foundations under horizontal loading [texte imprimé] / J. A. Knappett, Auteur ; M. J. Brown, Auteur ; M. F. Bransby, Auteur . - 2012 . - pp. 811 –823. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 811 –823 Mots-clés : Sands  Footings/foundations  Offshore  engineering  Plasticity  Model  tests Résumé : Grillage foundations are an alternative to solid surface mudmats for supporting seabed infrastructure, offering improved hydrodynamic performance and savings in foundation material. Recent research has demonstrated that grillages can be designed to have similar vertical bearing capacity to a mudmat with the same footprint. This is extended herein by: (a) determining grillage performance under horizontal loading at constant vertical load (V-H); (b) the application and development of existing plasticity-based models for predicting performance; (c) comparing the V-H behaviour with surface mudmats; and (d) discussing the implications for design. Experimental tests were conducted in sands over a range of densities and in two different modes, representing different installation procedures. In over-penetrated tests, the foundations were installed to achieve a vertical bearing capacity V 0, followed by horizontal loading at a constant vertical load with V < V 0. In normally penetrated tests, foundations were installed to V 0 before horizontal loading at constant vertical load with V = V 0. Both normalised V-H yield surfaces and a plasticity-based simulation model are presented for use in design. Laboratory-scale grillages offer improved horizontal capacity in loose and medium-dense sands and similar horizontal capacity in very dense sand, compared with surface mudmats. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.012

Effects of axial load and slope arrangement on pile group response in laterally spreading soils / J. A. Knappett in Journal of geotechnical and geoenvironmental engineering, Vol. 138 N° 7 (Juillet 2012) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 138 N° 7 (Juillet 2012) . - pp. 799–809 Titre : Effects of axial load and slope arrangement on pile group response in laterally spreading soils Type de document : texte imprimé Auteurs : J. A. Knappett, Auteur ; S. P.G. Madabhushi, Auteur Année de publication : 2012 Article en page(s) : pp. 799–809 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Earthquake  engineering  Soil  liquefaction  Layered  soils  Pile  groups  Centrifuge  model Résumé : This paper presents the results of a series of dynamic centrifuge tests that were conducted for 2×2 pile groups in a three-layer laterally spreading soil profile consisting of a nonliquefiable cohesive crust overlying loose, liquefiable sand, overlying dense sand. Two main variables are considered, both of which received little attention in previous work on piles in laterally spreading soils, namely (1) the axial load carried by the foundation, and (2) whether the slope boundary conditions are infinite or finite. The data show that the presence of axial load reduces the lateral stiffness of the foundation resulting from P-Δ effects and reduces their capacity to resist lateral kinematic loads from spreading soil. This degradation in lateral response (bending) may be accompanied by substantial settlement of the foundation as a competing failure mode that must also be considered in design. Furthermore, the mechanical response of the liquefied soil appears to vary greatly with the slope boundary condition. This is particularly true at the interface between the liquefied sand and the cohesive crust, where the downslope displacement of the crust for infinite slopes is much greater than the underlying sand, with the reverse being true for finite slopes. The data also suggest an alternative mechanism to the water film concept that has been used previously to account for the large downslope movements of low permeability crustal layers. This fundamental difference in mechanical response provides insight that may lead to the improvement of simplified empirical methods for estimating surficial displacements caused by lateral spreading. ISSN : 1090-0241 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000654 [article] Effects of axial load and slope arrangement on pile group response in laterally spreading soils [texte imprimé] / J. A. Knappett, Auteur ; S. P.G. Madabhushi, Auteur . - 2012 . - pp. 799–809. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 138 N° 7 (Juillet 2012) . - pp. 799–809 Mots-clés : Earthquake  engineering  Soil  liquefaction  Layered  soils  Pile  groups  Centrifuge  model Résumé : This paper presents the results of a series of dynamic centrifuge tests that were conducted for 2×2 pile groups in a three-layer laterally spreading soil profile consisting of a nonliquefiable cohesive crust overlying loose, liquefiable sand, overlying dense sand. Two main variables are considered, both of which received little attention in previous work on piles in laterally spreading soils, namely (1) the axial load carried by the foundation, and (2) whether the slope boundary conditions are infinite or finite. The data show that the presence of axial load reduces the lateral stiffness of the foundation resulting from P-Δ effects and reduces their capacity to resist lateral kinematic loads from spreading soil. This degradation in lateral response (bending) may be accompanied by substantial settlement of the foundation as a competing failure mode that must also be considered in design. Furthermore, the mechanical response of the liquefied soil appears to vary greatly with the slope boundary condition. This is particularly true at the interface between the liquefied sand and the cohesive crust, where the downslope displacement of the crust for infinite slopes is much greater than the underlying sand, with the reverse being true for finite slopes. The data also suggest an alternative mechanism to the water film concept that has been used previously to account for the large downslope movements of low permeability crustal layers. This fundamental difference in mechanical response provides insight that may lead to the improvement of simplified empirical methods for estimating surficial displacements caused by lateral spreading. ISSN : 1090-0241 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000654

Lateral spreading forces on bridge piers and pile caps in laterally spreading soil / J. A. Knappett in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 12 (Décembre 2010) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 12 (Décembre 2010) . - pp. 1589-1599 Titre : Lateral spreading forces on bridge piers and pile caps in laterally spreading soil : effect of angle of incidence Type de document : texte imprimé Auteurs : J. A. Knappett, Auteur ; S. Mohammadi, Auteur ; C. Griffin, Auteur Année de publication : 2011 Article en page(s) : pp. 1589-1599 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Bridge  piers  Earthquakes  Lateral  loads  Pile  caps  Plastic  analysis  Soil  deformation Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : In this paper, the kinematic forces which may be applied to bridge piers or pile caps from laterally spreading surficial cohesive soil layers (nonliquefied crusts) through which they pass are considered. Such forces often represent the largest load component acting on a structure and/or foundation during liquefaction-induced lateral spreading. Both circular and square structural inclusions are considered, and particular attention is paid to the orientation of the inclusion to the direction of spreading, here defined as the angle of incidence (θ). Experimental modeling was conducted using a modified direct shearbox to simulate the spreading of kaolin past structural inclusions at various θ. Load-displacement data and particle image velocimetry analysis revealed that the ultimate load for both square and circular cases may be determined using a wedge-based upper-bound plasticity analysis. For circular sections, this ultimate load is independent of θ due to radial symmetry. The ultimate load on square sections was found to depend more significantly on θ and a simple analytical method is presented to account for this. The method suggests that the ultimate loads acting on square bridge piers or pile caps will be a maximum when the spreading soil impinges on the corners of the inclusion, at which time the ultimate load will be 19–26% larger (depending on the soil-structure interface roughness) than for spreading impinging on the edge of the inclusion. Experimental tests suggested a value of 22%. Finally, the tests support previous results suggesting that when the underlying soil is unable to carry redistributed shear stress (i.e., when it is liquefied) load-displacement curves in the crustal layers are less stiff than for typical retaining structures under static conditions. The displacement at soil yield was found to be between 20–30% of the height of the inclusion in the layer, and also depends on θ in the case of square inclusions. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v136/i12/p1589_s1?isAuthorized=no [article] Lateral spreading forces on bridge piers and pile caps in laterally spreading soil : effect of angle of incidence [texte imprimé] / J. A. Knappett, Auteur ; S. Mohammadi, Auteur ; C. Griffin, Auteur . - 2011 . - pp. 1589-1599. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 12 (Décembre 2010) . - pp. 1589-1599 Mots-clés : Bridge  piers  Earthquakes  Lateral  loads  Pile  caps  Plastic  analysis  Soil  deformation Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : In this paper, the kinematic forces which may be applied to bridge piers or pile caps from laterally spreading surficial cohesive soil layers (nonliquefied crusts) through which they pass are considered. Such forces often represent the largest load component acting on a structure and/or foundation during liquefaction-induced lateral spreading. Both circular and square structural inclusions are considered, and particular attention is paid to the orientation of the inclusion to the direction of spreading, here defined as the angle of incidence (θ). Experimental modeling was conducted using a modified direct shearbox to simulate the spreading of kaolin past structural inclusions at various θ. Load-displacement data and particle image velocimetry analysis revealed that the ultimate load for both square and circular cases may be determined using a wedge-based upper-bound plasticity analysis. For circular sections, this ultimate load is independent of θ due to radial symmetry. The ultimate load on square sections was found to depend more significantly on θ and a simple analytical method is presented to account for this. The method suggests that the ultimate loads acting on square bridge piers or pile caps will be a maximum when the spreading soil impinges on the corners of the inclusion, at which time the ultimate load will be 19–26% larger (depending on the soil-structure interface roughness) than for spreading impinging on the edge of the inclusion. Experimental tests suggested a value of 22%. Finally, the tests support previous results suggesting that when the underlying soil is unable to carry redistributed shear stress (i.e., when it is liquefied) load-displacement curves in the crustal layers are less stiff than for typical retaining structures under static conditions. The displacement at soil yield was found to be between 20–30% of the height of the inclusion in the layer, and also depends on θ in the case of square inclusions. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v136/i12/p1589_s1?isAuthorized=no

Liquefaction-induced settlement of pile groups in liquefiable and laterally spreading soils / J. A. Knappett in Journal of geotechnical and geoenvironmental engineering, Vol. 134 n°11 (Novembre 2008) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 134 n°11 (Novembre 2008) . - pp. 1609–1618 Titre : Liquefaction-induced settlement of pile groups in liquefiable and laterally spreading soils Type de document : texte imprimé Auteurs : J. A. Knappett, Auteur ; S. P. Madabhushi, Auteur Année de publication : 2009 Article en page(s) : pp. 1609–1618 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Earthquake  engineering  Liquefaction  Pile  groups  Pile  settlement  Lateral  displacement  Centrifuge  model  Seismic  design Résumé : The results of a series of dynamic centrifuge tests on model pile groups in (level) liquefied and laterally spreading soil profiles are presented. The piles are axially loaded at typical working loads, which has enabled liquefaction-induced settlements of the foundations to be studied. The development of excess pore pressures within the bearing layer (dense sand) was found to lead to a reduction in pile capacity and potentially damagingly large coseismic settlements. As the excess pore pressure increased, these settlements were observed to exceed postshaking downdrag-induced settlements, which occur due to the reconsolidation of liquefied sand around the pile shaft. In resisting settlement, the pile cap was found to play an important role by compensating for the capacity lost by the piles. This was shown to be achieved by the development of dilative excess pore pressures beneath the pile cap within the underlying loose liquefied sand which provide increasing bearing capacity with settlement. The centrifuge test data show good qualitative and quantitative agreement with the limited amount of model and full-scale data currently available in the literature. The implications of settlement for the design of piled foundations to serviceability conditions in both level and sloping ground are discussed, with settlement becoming an increasingly important consideration for laterally stiffer piles. Finally, empirical relationships have been derived from the test data to relate suitable static safety factors to given increases in excess pore pressure in the bearing layer within a performance-based design framework (i.e., based on limiting displacements). En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A11%281 [...] [article] Liquefaction-induced settlement of pile groups in liquefiable and laterally spreading soils [texte imprimé] / J. A. Knappett, Auteur ; S. P. Madabhushi, Auteur . - 2009 . - pp. 1609–1618. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 134 n°11 (Novembre 2008) . - pp. 1609–1618 Mots-clés : Earthquake  engineering  Liquefaction  Pile  groups  Pile  settlement  Lateral  displacement  Centrifuge  model  Seismic  design Résumé : The results of a series of dynamic centrifuge tests on model pile groups in (level) liquefied and laterally spreading soil profiles are presented. The piles are axially loaded at typical working loads, which has enabled liquefaction-induced settlements of the foundations to be studied. The development of excess pore pressures within the bearing layer (dense sand) was found to lead to a reduction in pile capacity and potentially damagingly large coseismic settlements. As the excess pore pressure increased, these settlements were observed to exceed postshaking downdrag-induced settlements, which occur due to the reconsolidation of liquefied sand around the pile shaft. In resisting settlement, the pile cap was found to play an important role by compensating for the capacity lost by the piles. This was shown to be achieved by the development of dilative excess pore pressures beneath the pile cap within the underlying loose liquefied sand which provide increasing bearing capacity with settlement. The centrifuge test data show good qualitative and quantitative agreement with the limited amount of model and full-scale data currently available in the literature. The implications of settlement for the design of piled foundations to serviceability conditions in both level and sloping ground are discussed, with settlement becoming an increasingly important consideration for laterally stiffer piles. Finally, empirical relationships have been derived from the test data to relate suitable static safety factors to given increases in excess pore pressure in the bearing layer within a performance-based design framework (i.e., based on limiting displacements). En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A11%281 [...]

Liquefaction-induced settlement of pile groups in liquefiable and laterally spreading soils / J. A. Knappett in Journal of geotechnical and geoenvironmental engineering, Vol. 134 n°11 (Novembre 2008) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 134 n°11 (Novembre 2008) . - pp. 1609–1618 Titre : Liquefaction-induced settlement of pile groups in liquefiable and laterally spreading soils Type de document : texte imprimé Auteurs : J. A. Knappett, Auteur ; S. P. Madabhushi, Auteur Année de publication : 2009 Article en page(s) : pp. 1609–1618 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Earthquake  engineering  Liquefaction  Pile  groups  Pile  settlement  Lateral  displacement  Centrifuge  model  Seismic  design Résumé : The results of a series of dynamic centrifuge tests on model pile groups in (level) liquefied and laterally spreading soil profiles are presented. The piles are axially loaded at typical working loads, which has enabled liquefaction-induced settlements of the foundations to be studied. The development of excess pore pressures within the bearing layer (dense sand) was found to lead to a reduction in pile capacity and potentially damagingly large coseismic settlements. As the excess pore pressure increased, these settlements were observed to exceed postshaking downdrag-induced settlements, which occur due to the reconsolidation of liquefied sand around the pile shaft. In resisting settlement, the pile cap was found to play an important role by compensating for the capacity lost by the piles. This was shown to be achieved by the development of dilative excess pore pressures beneath the pile cap within the underlying loose liquefied sand which provide increasing bearing capacity with settlement. The centrifuge test data show good qualitative and quantitative agreement with the limited amount of model and full-scale data currently available in the literature. The implications of settlement for the design of piled foundations to serviceability conditions in both level and sloping ground are discussed, with settlement becoming an increasingly important consideration for laterally stiffer piles. Finally, empirical relationships have been derived from the test data to relate suitable static safety factors to given increases in excess pore pressure in the bearing layer within a performance-based design framework (i.e., based on limiting displacements). En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A11%281 [...] [article] Liquefaction-induced settlement of pile groups in liquefiable and laterally spreading soils [texte imprimé] / J. A. Knappett, Auteur ; S. P. Madabhushi, Auteur . - 2009 . - pp. 1609–1618. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 134 n°11 (Novembre 2008) . - pp. 1609–1618 Mots-clés : Earthquake  engineering  Liquefaction  Pile  groups  Pile  settlement  Lateral  displacement  Centrifuge  model  Seismic  design Résumé : The results of a series of dynamic centrifuge tests on model pile groups in (level) liquefied and laterally spreading soil profiles are presented. The piles are axially loaded at typical working loads, which has enabled liquefaction-induced settlements of the foundations to be studied. The development of excess pore pressures within the bearing layer (dense sand) was found to lead to a reduction in pile capacity and potentially damagingly large coseismic settlements. As the excess pore pressure increased, these settlements were observed to exceed postshaking downdrag-induced settlements, which occur due to the reconsolidation of liquefied sand around the pile shaft. In resisting settlement, the pile cap was found to play an important role by compensating for the capacity lost by the piles. This was shown to be achieved by the development of dilative excess pore pressures beneath the pile cap within the underlying loose liquefied sand which provide increasing bearing capacity with settlement. The centrifuge test data show good qualitative and quantitative agreement with the limited amount of model and full-scale data currently available in the literature. The implications of settlement for the design of piled foundations to serviceability conditions in both level and sloping ground are discussed, with settlement becoming an increasingly important consideration for laterally stiffer piles. Finally, empirical relationships have been derived from the test data to relate suitable static safety factors to given increases in excess pore pressure in the bearing layer within a performance-based design framework (i.e., based on limiting displacements). En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A11%281 [...]

Small-scale modeling of reinforced concrete structural elements for use in a geotechnical centrifuge / J. A. Knappett in Journal of structural engineering, Vol. 137 N° 11 (Novembre 2011) 

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