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

Consolidation around partially embedded seabed pipelines / K. Krost in Géotechnique, Vol. 61 N° 2 (Fevrier 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 2 (Fevrier 2011) . - pp. 167–173 Titre : Consolidation around partially embedded seabed pipelines Type de document : texte imprimé Auteurs : K. Krost, Auteur ; S. M. Gourvenec, Auteur ; D. J. White, Auteur Année de publication : 2011 Article en page(s) : pp. 167–173 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Offshore  engineering  Soil/Structure  interaction  Consolidation  numerical  modelling Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : When a pipeline is laid on a soft clay seabed, excess pore pressure is generated. During the subsequent dissipation process, the effective stress at the pipe–soil interface and the available axial pipe–soil resistance rise. This ‘set-up' of axial resistance is an important consideration in various aspects of pipeline design, including the mitigation of thermal and pressure-induced expansion, the stability of the pipeline on sloping ground and the assessment of pipe–soil forces during installation. A set of finite-element analyses has been conducted to assess the pore pressure dissipation and consolidation beneath partially embedded seabed pipelines, extending existing solutions for strip footings. It is shown that the curved shape of a pipeline increases the normalised rate of consolidation compared with a strip footing. Dissipation curves for various levels of embedment are presented and the calculated response is shown to compare well with data from a field test conducted on a soft clay. The dissipation curves have been used to derive the development of effective contact force between the pipe and the seabed as consolidation progresses. These results highlight the significant enhancement of this force – and therefore the available axial resistance – that arises from a ‘wedging effect' related to the curvature of the pipe–soil contact surface. This wedging effect leads to a beneficial enhancement of the axial resistance. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.t.015 [article] Consolidation around partially embedded seabed pipelines [texte imprimé] / K. Krost, Auteur ; S. M. Gourvenec, Auteur ; D. J. White, Auteur . - 2011 . - pp. 167–173. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 2 (Fevrier 2011) . - pp. 167–173 Mots-clés : Offshore  engineering  Soil/Structure  interaction  Consolidation  numerical  modelling Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : When a pipeline is laid on a soft clay seabed, excess pore pressure is generated. During the subsequent dissipation process, the effective stress at the pipe–soil interface and the available axial pipe–soil resistance rise. This ‘set-up' of axial resistance is an important consideration in various aspects of pipeline design, including the mitigation of thermal and pressure-induced expansion, the stability of the pipeline on sloping ground and the assessment of pipe–soil forces during installation. A set of finite-element analyses has been conducted to assess the pore pressure dissipation and consolidation beneath partially embedded seabed pipelines, extending existing solutions for strip footings. It is shown that the curved shape of a pipeline increases the normalised rate of consolidation compared with a strip footing. Dissipation curves for various levels of embedment are presented and the calculated response is shown to compare well with data from a field test conducted on a soft clay. The dissipation curves have been used to derive the development of effective contact force between the pipe and the seabed as consolidation progresses. These results highlight the significant enhancement of this force – and therefore the available axial resistance – that arises from a ‘wedging effect' related to the curvature of the pipe–soil contact surface. This wedging effect leads to a beneficial enhancement of the axial resistance. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.t.015

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) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 6 (Juin 2009) . - pp. 819–829 Titre : Effect of surface heave on response of partially embedded pipelines on clay Type de document : texte imprimé Auteurs : R. S. Merifield, Auteur ; D. J. White, Auteur ; M. F. Randolph, Auteur Année de publication : 2009 Article en page(s) : pp. 819–829 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Pipelines  Clays  Plasticity  Offshore  structures  Finite  element  method  Soil  mechanics  Collapse  loads  Cohesive  soils  Embedment Résumé : The as-laid embedment of an on-bottom pipeline strongly influences the resulting thermal insulation, and the resistance to subsequent axial and lateral movement of the pipeline. Reliable assessment of these parameters is essential for the design of offshore pipelines. Static vertical penetration of a pipe into a soft clay seabed—which can be modeled as an undrained process—causes heave of soil on each side of the pipeline. The heaved soil contributes to the vertical penetration resistance and the horizontal capacity. This paper describes a series of large deformation finite-element analyses of pipe penetration, supported by a simple analytical assessment of the heave process. The conventional bearing capacity approach to the analysis of pipe penetration is reviewed, and modifications for the effects of soil weight and heave are presented. It is shown that in soft soil conditions—which are typical for deep water—the soil self-weight contributes a significant portion of the vertical penetration resistance and horizontal capacity. If heave is neglected, the soil weight leads to a vertical force due to buoyancy, based on Archimedes’ principle. When heave is considered, the soil weight contributes an additional component of vertical load, exceeding simple buoyancy, due to the distorted geometry of the soil surface. Archimedes’ principle does not apply. The finite-element analyses, benchmarked against rigorous plasticity solutions, are used to calibrate simple expressions for predicting static vertical pipe penetration, and the resulting horizontal capacity. These simple solutions allow the conventional bearing capacity approach to be used in a manner which correctly accounts for the effects of soil self-weight and heave. An approximate solution for predicting the “local” pipe embedment—relative to the raised soil level immediately adjacent to the pipe—is derived. The local embedment significantly exceeds the nominal embedment relative to the original soil surface. This effect counteracts the tendency for heave to reduce the embedment by raising the penetration resistance. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000070 [article] Effect of surface heave on response of partially embedded pipelines on clay [texte imprimé] / R. S. Merifield, Auteur ; D. J. White, Auteur ; M. F. Randolph, Auteur . - 2009 . - pp. 819–829. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 6 (Juin 2009) . - pp. 819–829 Mots-clés : Pipelines  Clays  Plasticity  Offshore  structures  Finite  element  method  Soil  mechanics  Collapse  loads  Cohesive  soils  Embedment Résumé : The as-laid embedment of an on-bottom pipeline strongly influences the resulting thermal insulation, and the resistance to subsequent axial and lateral movement of the pipeline. Reliable assessment of these parameters is essential for the design of offshore pipelines. Static vertical penetration of a pipe into a soft clay seabed—which can be modeled as an undrained process—causes heave of soil on each side of the pipeline. The heaved soil contributes to the vertical penetration resistance and the horizontal capacity. This paper describes a series of large deformation finite-element analyses of pipe penetration, supported by a simple analytical assessment of the heave process. The conventional bearing capacity approach to the analysis of pipe penetration is reviewed, and modifications for the effects of soil weight and heave are presented. It is shown that in soft soil conditions—which are typical for deep water—the soil self-weight contributes a significant portion of the vertical penetration resistance and horizontal capacity. If heave is neglected, the soil weight leads to a vertical force due to buoyancy, based on Archimedes’ principle. When heave is considered, the soil weight contributes an additional component of vertical load, exceeding simple buoyancy, due to the distorted geometry of the soil surface. Archimedes’ principle does not apply. The finite-element analyses, benchmarked against rigorous plasticity solutions, are used to calibrate simple expressions for predicting static vertical pipe penetration, and the resulting horizontal capacity. These simple solutions allow the conventional bearing capacity approach to be used in a manner which correctly accounts for the effects of soil self-weight and heave. An approximate solution for predicting the “local” pipe embedment—relative to the raised soil level immediately adjacent to the pipe—is derived. The local embedment significantly exceeds the nominal embedment relative to the original soil surface. This effect counteracts the tendency for heave to reduce the embedment by raising the penetration resistance. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000070

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

Public ISBD [article]  in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 787 –798 Titre : Field observations of as-laid pipeline embedment in carbonate sediments Type de document : texte imprimé Auteurs : Z. J. Westgate, Auteur ; D. J. White, Auteur ; M. F. Randolph, Auteur Année de publication : 2012 Article en page(s) : pp. 787 –798 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Soil/structure  interaction  Offshore  engineering  Calcareous  soils Résumé : Reliable prediction of the embedment of untrenched subsea pipelines is of increasing importance as hydrocarbon developments progress into deeper waters, located further from shore. Pipeline design issues such as hydrodynamic stability, lateral buckling and axial walking require accurate assessment of the pipe embedment, in order to assess correctly the pipe–soil resistance forces and the thermal insulation provided by the soil. This study presents a detailed back-analysis of the laying process and the as-laid condition of a pipeline on carbonate sediments. The pipe embedment is linked to the relevant soil properties, metocean conditions, vessel motions, and lay geometry along the route. A cycle-by-cycle framework is proposed for the development of embedment as the pipe is subjected to oscillations during laying. The calculations use parameters obtained from standard in situ tests, and are applied across a range of soil and lay conditions along this particular pipeline route. The proposed calculation framework incorporates the effect of the lay rate and the pipeline catenary on the embedment process. It offers a significant improvement on the current practice of applying empirical multiplicative factors to the calculated static embedment in order to account for dynamic lay effects. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.001 [article] Field observations of as-laid pipeline embedment in carbonate sediments [texte imprimé] / Z. J. Westgate, Auteur ; D. J. White, Auteur ; M. F. Randolph, Auteur . - 2012 . - pp. 787 –798. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 787 –798 Mots-clés : Soil/structure  interaction  Offshore  engineering  Calcareous  soils Résumé : Reliable prediction of the embedment of untrenched subsea pipelines is of increasing importance as hydrocarbon developments progress into deeper waters, located further from shore. Pipeline design issues such as hydrodynamic stability, lateral buckling and axial walking require accurate assessment of the pipe embedment, in order to assess correctly the pipe–soil resistance forces and the thermal insulation provided by the soil. This study presents a detailed back-analysis of the laying process and the as-laid condition of a pipeline on carbonate sediments. The pipe embedment is linked to the relevant soil properties, metocean conditions, vessel motions, and lay geometry along the route. A cycle-by-cycle framework is proposed for the development of embedment as the pipe is subjected to oscillations during laying. The calculations use parameters obtained from standard in situ tests, and are applied across a range of soil and lay conditions along this particular pipeline route. The proposed calculation framework incorporates the effect of the lay rate and the pipeline catenary on the embedment process. It offers a significant improvement on the current practice of applying empirical multiplicative factors to the calculated static embedment in order to account for dynamic lay effects. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.001

Limit analysis of the undrained bearing capacity of offshore pipelines / C. M. Martin in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 847 –863 Titre : Limit analysis of the undrained bearing capacity of offshore pipelines Type de document : texte imprimé Auteurs : C. M. Martin, Auteur ; D. J. White, Auteur Année de publication : 2012 Article en page(s) : pp. 847 –863 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Clays  Pipelines  Numerical  modelling  Bearing  capacity  Offshore  engineering Résumé : The ultimate bearing capacity of a rigid, plane-strain pipe segment embedded in undrained clay is studied using numerical limit analysis. The pipe is considered to be ‘wished in place' at invert penetrations ranging from zero to five pipe diameters, thus providing coverage of both on-bottom (partially embedded) and trenched (fully embedded) offshore pipelines. The soil is modelled as a rigid-plastic Tresca material with either uniform strength or strength proportional to depth. The effects of soil weight, interface roughness and interface tensile capacity are investigated in a systematic manner. All calculations are performed using the finite-element limit analysis code OxLim, which uses adaptive mesh refinement to compute tightly bracketed lower- and upper-bound plasticity solutions. The velocity fields from the upper-bound analyses provide the corresponding failure mechanisms. The paper initially focuses on purely vertical loading (penetration and uplift), and then addresses combined vertical and horizontal loading. A comprehensive set of design curves and failure envelopes is presented, with the results explained in terms of the changing failure mechanisms. These results are immediately applicable in practice. In particular, current industry-standard procedures for design against pipeline upheaval are critically reviewed, and are shown to have potentially unconservative shortcomings. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.016 [article] Limit analysis of the undrained bearing capacity of offshore pipelines [texte imprimé] / C. M. Martin, Auteur ; D. J. White, Auteur . - 2012 . - pp. 847 –863. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 847 –863 Mots-clés : Clays  Pipelines  Numerical  modelling  Bearing  capacity  Offshore  engineering Résumé : The ultimate bearing capacity of a rigid, plane-strain pipe segment embedded in undrained clay is studied using numerical limit analysis. The pipe is considered to be ‘wished in place' at invert penetrations ranging from zero to five pipe diameters, thus providing coverage of both on-bottom (partially embedded) and trenched (fully embedded) offshore pipelines. The soil is modelled as a rigid-plastic Tresca material with either uniform strength or strength proportional to depth. The effects of soil weight, interface roughness and interface tensile capacity are investigated in a systematic manner. All calculations are performed using the finite-element limit analysis code OxLim, which uses adaptive mesh refinement to compute tightly bracketed lower- and upper-bound plasticity solutions. The velocity fields from the upper-bound analyses provide the corresponding failure mechanisms. The paper initially focuses on purely vertical loading (penetration and uplift), and then addresses combined vertical and horizontal loading. A comprehensive set of design curves and failure envelopes is presented, with the results explained in terms of the changing failure mechanisms. These results are immediately applicable in practice. In particular, current industry-standard procedures for design against pipeline upheaval are critically reviewed, and are shown to have potentially unconservative shortcomings. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.016

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

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Modelling the dynamic embedment of seabed pipelines / C. Y. Cheuk in Géotechnique, Vol. LXI N° 1 (Janvier 2011) 

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The effects of penetration rate and strain softening on the vertical penetration resistance of seabed pipelines / S. Chatterjee in Géotechnique, Vol. 62 N° 7 (Juillet 2012) 

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The mechanism of steady friction between seabed pipelines and clay soils / D. J. White in Géotechnique, Vol. 61 N° 12 (Décembre 2011) 

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Uplift mechanisms of pipes buried in sand / C. Y. Cheuk in Journal of geotechnical and geoenvironmental engineering, Vol. 134 N°2 (Fevrier 2008) 

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