Documents disponibles écrits par cet auteur

Analytical modelling of the steady flow of a submarine slide and consequent loading on a pipeline / N. Boukpeti in Géotechnique, Vol. 62 N° 2 (Fevrier 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 2 (Fevrier 2012) . - pp. 137 –146 Titre : Analytical modelling of the steady flow of a submarine slide and consequent loading on a pipeline Type de document : texte imprimé Auteurs : N. Boukpeti, Auteur ; D. J. White, Auteur ; M. F. Randolph, Auteur Année de publication : 2012 Article en page(s) : pp. 137 –146 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Constitutive  relations  Clays  Landslides  Shear  strength Résumé : This paper considers a simple one-dimensional model of a submarine slide at a steady state. From equilibrium relations, the distributions of shear stress, velocity and strain rate across the slide thickness are determined analytically for two rate-dependent soil strength models. Previous work has demonstrated that the increase in shear strength with strain rate can be adequately described using a power law or a logarithmic law model. The analytical solutions obtained with these models are compared with the ones available for a viscoplastic fluid of the Bingham or Herschel–Bulkley types. The influence of the rheological parameters, the slope angle and the slide thickness on the flow and deformation characteristics is analysed for each model. The derived analytical solutions can be viewed as representing a particular position within a slide at a given instant in time. They can be used in conjunction with numerical modelling of the entire slide to provide some insights into the flow pattern, and into the parameter sensitivity. These solutions are also applicable to determination of the loading on a pipeline that is oriented across the path of the slide. They are used to illustrate the relative contributions of the soil strength and the inertial drag, as well as the influence of the vertical position of the pipeline within the slide. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.P.001 [article] Analytical modelling of the steady flow of a submarine slide and consequent loading on a pipeline [texte imprimé] / N. Boukpeti, Auteur ; D. J. White, Auteur ; M. F. Randolph, Auteur . - 2012 . - pp. 137 –146. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 2 (Fevrier 2012) . - pp. 137 –146 Mots-clés : Constitutive  relations  Clays  Landslides  Shear  strength Résumé : This paper considers a simple one-dimensional model of a submarine slide at a steady state. From equilibrium relations, the distributions of shear stress, velocity and strain rate across the slide thickness are determined analytically for two rate-dependent soil strength models. Previous work has demonstrated that the increase in shear strength with strain rate can be adequately described using a power law or a logarithmic law model. The analytical solutions obtained with these models are compared with the ones available for a viscoplastic fluid of the Bingham or Herschel–Bulkley types. The influence of the rheological parameters, the slope angle and the slide thickness on the flow and deformation characteristics is analysed for each model. The derived analytical solutions can be viewed as representing a particular position within a slide at a given instant in time. They can be used in conjunction with numerical modelling of the entire slide to provide some insights into the flow pattern, and into the parameter sensitivity. These solutions are also applicable to determination of the loading on a pipeline that is oriented across the path of the slide. They are used to illustrate the relative contributions of the soil strength and the inertial drag, as well as the influence of the vertical position of the pipeline within the slide. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.10.P.001

Centrifuge study of capacity of a skirted foundation under eccentric transient and sustained uplift / H. E. Acosta-Martinez in Géotechnique, Vol. 62 N° 4 (Avril 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 4 (Avril 2012) . - pp. 317–328 Titre : Centrifuge study of capacity of a skirted foundation under eccentric transient and sustained uplift Type de document : texte imprimé Auteurs : H. E. Acosta-Martinez, Auteur ; S. Gourvenec, Auteur ; M. F. Randolph, Auteur Année de publication : 2012 Article en page(s) : pp. 317–328 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Bearing  capacity  Clays  Foundations  Model  tests  Offshore  engineering  Pore  pressures  Time  dependence Résumé : Environmental and buoyancy forces impart overturning moments and potentially direct uplift to offshore foundation systems. Shallow skirted foundations are an attractive design solution, as negative excess pore pressures developed within the soil plug provide temporary uplift resistance. This paper presents the results of beam centrifuge tests on a shallow skirted foundation in a lightly overconsolidated clay under eccentric transient and sustained uplift. When compared with the response under concentric uplift, the experimental results show a reduction in capacity and an increase in the rate of degradation of capacity under sustained loading. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/issue/geot/62/4# [article] Centrifuge study of capacity of a skirted foundation under eccentric transient and sustained uplift [texte imprimé] / H. E. Acosta-Martinez, Auteur ; S. Gourvenec, Auteur ; M. F. Randolph, Auteur . - 2012 . - pp. 317–328. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 4 (Avril 2012) . - pp. 317–328 Mots-clés : Bearing  capacity  Clays  Foundations  Model  tests  Offshore  engineering  Pore  pressures  Time  dependence Résumé : Environmental and buoyancy forces impart overturning moments and potentially direct uplift to offshore foundation systems. Shallow skirted foundations are an attractive design solution, as negative excess pore pressures developed within the soil plug provide temporary uplift resistance. This paper presents the results of beam centrifuge tests on a shallow skirted foundation in a lightly overconsolidated clay under eccentric transient and sustained uplift. When compared with the response under concentric uplift, the experimental results show a reduction in capacity and an increase in the rate of degradation of capacity under sustained loading. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/issue/geot/62/4#

Deep-penetrating spudcan foundations on layered clays / M. S. Hossain in Géotechnique, Vol. 60 N° 3 (Mars 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 3 (Mars 2010) . - pp.157–170 Titre : Deep-penetrating spudcan foundations on layered clays : centrifuge tests Type de document : texte imprimé Auteurs : M. S. Hossain, Auteur ; M. F. Randolph, Auteur Année de publication : 2011 Article en page(s) : pp.157–170 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Bearing  capacity  Offshore  engineering  Footings/foundations  Centrifuge  modelling  Failure  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Installation of independent-legged jack-up rigs in sea-bed sediments where a strong layer overlays weaker soil can lead to catastrophic ‘punch-through', with potential leg buckling or toppling of the unit. Although approximate methods of analysis exist for estimating the penetration resistance, these do not account for the distortion of the upper layer as it punches through into the lower layer and there has been only limited visual depiction of the failure mechanism that occurs for the case of strong clay overlying weaker soil. This paper reports results of centrifuge model tests undertaken to provide insight into spudcan foundation behaviour during undrained vertical penetration through a stronger clay layer into weaker material, varying the strength ratio between lower and upper soil layers, the thickness of the upper layer relative to the spudcan diameter and the strength gradient of the lower layer. The model tests included half-spudcan tests against a transparent window, allowing the soil flow to be captured continuously by a digital camera and subsequently quantified through particle image velocimetry (PIV) analysis, and separate full-spudcan tests to measure the penetration resistance. Four interesting aspects of the soil flow mechanisms were identified: (a) vertically downwards motion of the soil and consequent deformation of the layer interface; (b) trapping of the stronger material beneath the spudcan, with this material being carried down into the underlying soft layer; (c) delayed back-flow of soil around the spudcan into the cavity formed above the spudcan; (d) eventual localised flow around the embedded spudcan. The effect of normalised layer soil properties and geometry on the soil flow mechanisms and the form of the penetration resistance profile is discussed in the context of the likelihood and severity of punch-through failure. Typical critical failure modes involved punching shear, with clear shear planes in the shape of a truncated cone forming in the upper layer below the spudcan. Potential punch-through, with a peak in penetration resistance followed by some reduction, occurred for almost all cases investigated. The reduction in resistance became more severe as the strength ratio of the underlying layer to the upper layer reduced, and also as the upper layer thickness increased. The failure modes assumed by the currently available recommended practices are not consistent with those observed from the study, suggesting a more rational approach is needed. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.039 [article] Deep-penetrating spudcan foundations on layered clays : centrifuge tests [texte imprimé] / M. S. Hossain, Auteur ; M. F. Randolph, Auteur . - 2011 . - pp.157–170. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 3 (Mars 2010) . - pp.157–170 Mots-clés : Bearing  capacity  Offshore  engineering  Footings/foundations  Centrifuge  modelling  Failure  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Installation of independent-legged jack-up rigs in sea-bed sediments where a strong layer overlays weaker soil can lead to catastrophic ‘punch-through', with potential leg buckling or toppling of the unit. Although approximate methods of analysis exist for estimating the penetration resistance, these do not account for the distortion of the upper layer as it punches through into the lower layer and there has been only limited visual depiction of the failure mechanism that occurs for the case of strong clay overlying weaker soil. This paper reports results of centrifuge model tests undertaken to provide insight into spudcan foundation behaviour during undrained vertical penetration through a stronger clay layer into weaker material, varying the strength ratio between lower and upper soil layers, the thickness of the upper layer relative to the spudcan diameter and the strength gradient of the lower layer. The model tests included half-spudcan tests against a transparent window, allowing the soil flow to be captured continuously by a digital camera and subsequently quantified through particle image velocimetry (PIV) analysis, and separate full-spudcan tests to measure the penetration resistance. Four interesting aspects of the soil flow mechanisms were identified: (a) vertically downwards motion of the soil and consequent deformation of the layer interface; (b) trapping of the stronger material beneath the spudcan, with this material being carried down into the underlying soft layer; (c) delayed back-flow of soil around the spudcan into the cavity formed above the spudcan; (d) eventual localised flow around the embedded spudcan. The effect of normalised layer soil properties and geometry on the soil flow mechanisms and the form of the penetration resistance profile is discussed in the context of the likelihood and severity of punch-through failure. Typical critical failure modes involved punching shear, with clear shear planes in the shape of a truncated cone forming in the upper layer below the spudcan. Potential punch-through, with a peak in penetration resistance followed by some reduction, occurred for almost all cases investigated. The reduction in resistance became more severe as the strength ratio of the underlying layer to the upper layer reduced, and also as the upper layer thickness increased. The failure modes assumed by the currently available recommended practices are not consistent with those observed from the study, suggesting a more rational approach is needed. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.039

Deep-penetrating spudcan foundations on layered clays / M. S. Hossain in Géotechnique, Vol. 60 N° 3 (Mars 2010) 

Public ISBD [article]  in Géotechnique > Vol. 60 N° 3 (Mars 2010) . - pp. 171–184 Titre : Deep-penetrating spudcan foundations on layered clays : numerical analysis Type de document : texte imprimé Auteurs : M. S. Hossain, Auteur ; M. F. Randolph, Auteur Année de publication : 2011 Article en page(s) : pp. 171–184 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Offshore  engineering  Numerical  modelling  Bearing  capacity  Footings/foundations  Failure  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper presents results of large deformation finite element (LDFE) analyses that investigate the penetration response of deep-penetrating spudcan foundations in stratified soil comprising a strong clay layer overlying weaker clay. Such strength profiles give rise to potential punch-through failure, with a local maximum penetration resistance followed by some reduction. The paper is a companion paper to one that presents results from centrifuge model tests of the same problem, with the overall aim being to investigate the potential for punch-through failure and its severity, as a basis for improving design methods for evaluating spudcan penetration. The LDFE analyses have simulated continuous penetration of smooth and rough spudcan foundations from the sea-bed surface. A detailed parametric study has been undertaken, exploring the relevant range of layer thickness (relative to the spudcan diameter), strength ratios and spudcan base roughness. The results have been validated against previously published results and the centrifuge test data presented in a companion paper. Excellent agreement was obtained between the results from LDFE analyses and centrifuge tests. As the ratio of the shear strength of the bottom layer to that of the top layer decreased, upwards soil flow around the spudcan shoulder became less pronounced and the failure mechanism was dominated by a steep-sided plug of soil from the top layer being forced deep into the lower layer. The potential for severe punch-through was demonstrated by a significant reduction in the resistance profile as the spudcan approached the interface between the two layers. A preliminary design chart is proposed to estimate the cavity depth above the penetrating spudcan, which was significantly greater than that for a single layer clay. The penetration responses have been presented in terms of profiles of normalised net bearing pressure for a range of layer geometries and soil properties. Potential punch-through occurred for all cases where the strength ratio was less than or equal to 0·6, with the reduction in resistance being greater the lower the strength ratio of the underlying layer to the upper layer, and the thicker the upper layer, but reducing as the strength gradient in the lower layer increased. The current approach suggested in offshore design guidelines is shown to underestimate the penetration resistance significantly, in most cases, and give poor estimates of the likelihood and severity of spudcan punch-through. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.040 [article] Deep-penetrating spudcan foundations on layered clays : numerical analysis [texte imprimé] / M. S. Hossain, Auteur ; M. F. Randolph, Auteur . - 2011 . - pp. 171–184. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 60 N° 3 (Mars 2010) . - pp. 171–184 Mots-clés : Offshore  engineering  Numerical  modelling  Bearing  capacity  Footings/foundations  Failure  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper presents results of large deformation finite element (LDFE) analyses that investigate the penetration response of deep-penetrating spudcan foundations in stratified soil comprising a strong clay layer overlying weaker clay. Such strength profiles give rise to potential punch-through failure, with a local maximum penetration resistance followed by some reduction. The paper is a companion paper to one that presents results from centrifuge model tests of the same problem, with the overall aim being to investigate the potential for punch-through failure and its severity, as a basis for improving design methods for evaluating spudcan penetration. The LDFE analyses have simulated continuous penetration of smooth and rough spudcan foundations from the sea-bed surface. A detailed parametric study has been undertaken, exploring the relevant range of layer thickness (relative to the spudcan diameter), strength ratios and spudcan base roughness. The results have been validated against previously published results and the centrifuge test data presented in a companion paper. Excellent agreement was obtained between the results from LDFE analyses and centrifuge tests. As the ratio of the shear strength of the bottom layer to that of the top layer decreased, upwards soil flow around the spudcan shoulder became less pronounced and the failure mechanism was dominated by a steep-sided plug of soil from the top layer being forced deep into the lower layer. The potential for severe punch-through was demonstrated by a significant reduction in the resistance profile as the spudcan approached the interface between the two layers. A preliminary design chart is proposed to estimate the cavity depth above the penetrating spudcan, which was significantly greater than that for a single layer clay. The penetration responses have been presented in terms of profiles of normalised net bearing pressure for a range of layer geometries and soil properties. Potential punch-through occurred for all cases where the strength ratio was less than or equal to 0·6, with the reduction in resistance being greater the lower the strength ratio of the underlying layer to the upper layer, and the thicker the upper layer, but reducing as the strength gradient in the lower layer increased. The current approach suggested in offshore design guidelines is shown to underestimate the penetration resistance significantly, in most cases, and give poor estimates of the likelihood and severity of spudcan punch-through. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.040

Effect of installation method on external shaft friction of caissons in soft clay / W. Chen in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 5 (Mai 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 5 (Mai 2009) . - pp. 605–615 Titre : Effect of installation method on external shaft friction of caissons in soft clay Type de document : texte imprimé Auteurs : W. Chen, Auteur ; H. Zhou, Auteur ; M. F. Randolph, Auteur Année de publication : 2009 Article en page(s) : pp. 605–615 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Caissons  Centrifuge  models  Clays  Soft  soils  Finite  element  method  Skin  friction Résumé : The influence of the installation method on the soil flow pattern, resulting external radial total stress changes, and final external shaft friction after consolidation has been investigated for caissons in soft clay by means of centrifuge model tests, large deformation finite-element (FE) analysis, and a simple cavity expansion approach. Both the centrifuge measurements and the FE results show that more soil is forced into the caisson under suction than under jacking. However, the difference in the resulting external radial total stress changes or penetration-induced excess pore-water pressure is much less significant, since the expansion-induced excess pore pressure is smaller for thin-walled caissons than for driven piles. After subsequent consolidation, the influence of the installation method reduces further, and the final shaft friction ratios are close for the two installation methods. Based on the magnitude of heave ratios derived from the centrifuge measurements and the FE analysis, a simple form of cavity expansion approach can reasonably estimate external radial stress changes during installation and after consolidation, and final shaft friction ratios for the caissons. An approach for estimating the external shaft friction ratios for vertical pullout of sealed caissons is proposed. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000033 [article] Effect of installation method on external shaft friction of caissons in soft clay [texte imprimé] / W. Chen, Auteur ; H. Zhou, Auteur ; M. F. Randolph, Auteur . - 2009 . - pp. 605–615. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 5 (Mai 2009) . - pp. 605–615 Mots-clés : Caissons  Centrifuge  models  Clays  Soft  soils  Finite  element  method  Skin  friction Résumé : The influence of the installation method on the soil flow pattern, resulting external radial total stress changes, and final external shaft friction after consolidation has been investigated for caissons in soft clay by means of centrifuge model tests, large deformation finite-element (FE) analysis, and a simple cavity expansion approach. Both the centrifuge measurements and the FE results show that more soil is forced into the caisson under suction than under jacking. However, the difference in the resulting external radial total stress changes or penetration-induced excess pore-water pressure is much less significant, since the expansion-induced excess pore pressure is smaller for thin-walled caissons than for driven piles. After subsequent consolidation, the influence of the installation method reduces further, and the final shaft friction ratios are close for the two installation methods. Based on the magnitude of heave ratios derived from the centrifuge measurements and the FE analysis, a simple form of cavity expansion approach can reasonably estimate external radial stress changes during installation and after consolidation, and final shaft friction ratios for the caissons. An approach for estimating the external shaft friction ratios for vertical pullout of sealed caissons is proposed. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000033

Effect of shaft on resistance of a ball penetrometer / H. Zhou in Géotechnique, Vol. 61 N° 11 (Novembre 2010) 

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Effect of soil characteristics on relative values of piezocone, T-bar and ball penetration resistances / H. E. Low in Géotechnique, Vol. 61 N° 8 (Août 2011) 

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Effect of surface heave on response of partially embedded pipelines on clay / R. S. Merifield in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 6 (Juin 2009) 

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Field observations of as-laid pipeline embedment in carbonate sediments / Z. J. Westgate in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

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Geotechnical characterisation and engineering properties of Burswood clay / H. E. Low in Géotechnique, Vol. 61 N° 7 (Juillet 2011) 

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Geotechnical characterisation and engineering properties of Burswood clay / H. E. Low in Géotechnique, Vol. 62 N° 7 (Juillet 2012) 

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Modelling the axial soil resistance on deep-water pipelines / M. F. Randolph in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

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Pipe penetration in cohesive soil / J. D. Murff in Géotechnique, Vol. 39 N°2 (Juin 1989) 

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A plasticity model to assess the keying of plate anchors / M. J. Cassidy in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

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Setup Following Installation of Dynamic Anchors in Normally consolidated clay / M. D. Richardson in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 4 (Avril 2009) 

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