Dépouillements

Mechanical behaviour of gas-charged marine plastic sediments / N. Sultan in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 751 –766 Titre : Mechanical behaviour of gas-charged marine plastic sediments Type de document : texte imprimé Auteurs : N. Sultan, Auteur ; V. De Gennaro, Auteur ; A. Puech, Auteur Année de publication : 2012 Article en page(s) : pp. 751 –766 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Constitutive  relations  Offshore  engineering  Plasticity  Compressibility  Shear  strength Résumé : Understanding how free gas modifies the mechanical behaviour of marine plastic sediments remains a challenging issue. Special triaxial tests were carried out on natural sediments recovered from the Gulf of Guinea. Special attention was devoted to the laboratory preparation procedure, involving saturation of natural marine sediment samples with carbonated water and generation of free gas following undrained unloading. Experimental data show that soil destructuration and damage generated by gas expansion and exsolution are at the origin of (a) the increase in the isotropic compressibility and decrease in the preconsolidation pressure, and (b) the decrease in the peak undrained strength and abrupt increase of the pore pressure during undrained shearing. The experimental data also show that flooding of gas bubbles and dissolution of free gas do not imply a complete strength recovery of natural sediments. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.002 [article] Mechanical behaviour of gas-charged marine plastic sediments [texte imprimé] / N. Sultan, Auteur ; V. De Gennaro, Auteur ; A. Puech, Auteur . - 2012 . - pp. 751 –766. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 751 –766 Mots-clés : Constitutive  relations  Offshore  engineering  Plasticity  Compressibility  Shear  strength Résumé : Understanding how free gas modifies the mechanical behaviour of marine plastic sediments remains a challenging issue. Special triaxial tests were carried out on natural sediments recovered from the Gulf of Guinea. Special attention was devoted to the laboratory preparation procedure, involving saturation of natural marine sediment samples with carbonated water and generation of free gas following undrained unloading. Experimental data show that soil destructuration and damage generated by gas expansion and exsolution are at the origin of (a) the increase in the isotropic compressibility and decrease in the preconsolidation pressure, and (b) the decrease in the peak undrained strength and abrupt increase of the pore pressure during undrained shearing. The experimental data also show that flooding of gas bubbles and dissolution of free gas do not imply a complete strength recovery of natural sediments. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.002

Strain-rate effects in deep marine clays from the Gulf of Guinea / S. S. Torisu in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 767 –775 Titre : Strain-rate effects in deep marine clays from the Gulf of Guinea Type de document : texte imprimé Auteurs : S. S. Torisu, Auteur ; J. M. Pereira, Auteur ; V. De Gennaro, Auteur Année de publication : 2012 Article en page(s) : pp. 767 –775 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Creep  Laboratory  tests  Stress  path  Fabric/structure  of  soils  Time  dependence  Shear  strength  Clays Résumé : Current developments in deepwater offshore oil production in the Gulf of Guinea (GoG) make it necessary to characterise the mechanical behaviour of the GoG deepwater sediments better. This paper examines some aspects of the strain-rate-dependent behaviour of intact and reconstituted GoG clay specimens. Results from isotropic compression and undrained shearing laboratory tests with changing rates of stress and strain are presented. They show that the soil generally follows an isotach behaviour, with clear strain-rate dependence of the stress–strain behaviour and pore pressure response in the undrained shear tests. The effects of structure and its degradation on the time-dependent response of the sediments seem to confirm general trends observed in other structured clays. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.015 [article] Strain-rate effects in deep marine clays from the Gulf of Guinea [texte imprimé] / S. S. Torisu, Auteur ; J. M. Pereira, Auteur ; V. De Gennaro, Auteur . - 2012 . - pp. 767 –775. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 767 –775 Mots-clés : Creep  Laboratory  tests  Stress  path  Fabric/structure  of  soils  Time  dependence  Shear  strength  Clays Résumé : Current developments in deepwater offshore oil production in the Gulf of Guinea (GoG) make it necessary to characterise the mechanical behaviour of the GoG deepwater sediments better. This paper examines some aspects of the strain-rate-dependent behaviour of intact and reconstituted GoG clay specimens. Results from isotropic compression and undrained shearing laboratory tests with changing rates of stress and strain are presented. They show that the soil generally follows an isotach behaviour, with clear strain-rate dependence of the stress–strain behaviour and pore pressure response in the undrained shear tests. The effects of structure and its degradation on the time-dependent response of the sediments seem to confirm general trends observed in other structured clays. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.015

A numerical simulation of underwater slope failures generated by salt diapirism combined with active sedimentation / N. Kovacevic in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 777 –786 Titre : A numerical simulation of underwater slope failures generated by salt diapirism combined with active sedimentation Type de document : texte imprimé Auteurs : N. Kovacevic, Auteur ; R. J. Jardine, Auteur ; D. M. Potts, Auteur Année de publication : 2012 Article en page(s) : pp. 777 –786 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Failure  Numerical  modelling  Slopes  Landslides  Offshore  engineering Résumé : This paper describes advanced finite-element simulations of a geologically active and periodically unstable 700 m high underwater escarpment located in the Gulf of Mexico that has been created by uplifting salt diapirs combined with sediment deposition. The site's geological history, soil permeability and clay shear strength characteristics govern current slope stability, and determine the timing of any future failure. The geological and geotechnical conditions are reported before presenting fully coupled, large-displacement numerical simulations employing critical state formulations of the slope's evolution over the last 600 000 years. The latter form the basis for strain-softening analyses of the pore pressure equalisation and progressive failure processes that control current slope stability. The analyses also address the ground movement patterns that precede instability, giving useful information for geohazard risk assessment and early warning monitoring system design. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.004 [article] A numerical simulation of underwater slope failures generated by salt diapirism combined with active sedimentation [texte imprimé] / N. Kovacevic, Auteur ; R. J. Jardine, Auteur ; D. M. Potts, Auteur . - 2012 . - pp. 777 –786. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 777 –786 Mots-clés : Failure  Numerical  modelling  Slopes  Landslides  Offshore  engineering Résumé : This paper describes advanced finite-element simulations of a geologically active and periodically unstable 700 m high underwater escarpment located in the Gulf of Mexico that has been created by uplifting salt diapirs combined with sediment deposition. The site's geological history, soil permeability and clay shear strength characteristics govern current slope stability, and determine the timing of any future failure. The geological and geotechnical conditions are reported before presenting fully coupled, large-displacement numerical simulations employing critical state formulations of the slope's evolution over the last 600 000 years. The latter form the basis for strain-softening analyses of the pore pressure equalisation and progressive failure processes that control current slope stability. The analyses also address the ground movement patterns that precede instability, giving useful information for geohazard risk assessment and early warning monitoring system design. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.004

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

Centrifuge modelling of spudcan–pile interaction in soft clay / Y. Xie in Géotechnique, Vol. 62 N° 9 (Septembre 2012) 

Public ISBD [article]  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

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

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

Public ISBD [article]  in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 825 –836 Titre : A plasticity model to assess the keying of plate anchors Type de document : texte imprimé Auteurs : M. J. Cassidy, Auteur ; C. Gaudin, Auteur ; M. F. Randolph, Auteur Année de publication : 2012 Article en page(s) : pp. 825 –836 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Anchors  Plasticity  Numerical  modelling  Clays  Centrifuge  modelling  Offshore  engineering Résumé : Suction-embedded plate anchors (SEPLAs) have been developed to answer the growing need for anchors to withstand significant vertical loading. The concept combines the advantage of suction caissons (known penetration depth and location) and ‘drag-embedded' plate anchors (efficiency and low cost). The main issue associated with SEPLAs relates to the keying process, as the anchor is first loaded, and the associated loss of embedment and reduction in capacity. The paper presents a plasticity model developed to predict the trajectory and load development during anchor keying, and up to peak load. Rigid plasticity is assumed, allowing the kinematics of the anchor to be determined from a yield surface and associated plastic potential. The trajectory and performance of a typical SEPLA are predicted using the model, and are compared with results from centrifuge tests and large-deformation finite-element analysis. The anchor loss of embedment ranged from ∼0·2 to 1·5 times the anchor height for loading inclinations between 40° and 90° from the horizontal. The model was used further to calculate the anchor loss of embedment and capacity for varying padeye offsets. Results indicated that the loss of embedment could be reduced significantly by increasing the offset, but at the detriment of the ultimate anchor capacity. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.009 [article] A plasticity model to assess the keying of plate anchors [texte imprimé] / M. J. Cassidy, Auteur ; C. Gaudin, Auteur ; M. F. Randolph, Auteur . - 2012 . - pp. 825 –836. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 825 –836 Mots-clés : Anchors  Plasticity  Numerical  modelling  Clays  Centrifuge  modelling  Offshore  engineering Résumé : Suction-embedded plate anchors (SEPLAs) have been developed to answer the growing need for anchors to withstand significant vertical loading. The concept combines the advantage of suction caissons (known penetration depth and location) and ‘drag-embedded' plate anchors (efficiency and low cost). The main issue associated with SEPLAs relates to the keying process, as the anchor is first loaded, and the associated loss of embedment and reduction in capacity. The paper presents a plasticity model developed to predict the trajectory and load development during anchor keying, and up to peak load. Rigid plasticity is assumed, allowing the kinematics of the anchor to be determined from a yield surface and associated plastic potential. The trajectory and performance of a typical SEPLA are predicted using the model, and are compared with results from centrifuge tests and large-deformation finite-element analysis. The anchor loss of embedment ranged from ∼0·2 to 1·5 times the anchor height for loading inclinations between 40° and 90° from the horizontal. The model was used further to calculate the anchor loss of embedment and capacity for varying padeye offsets. Results indicated that the loss of embedment could be reduced significantly by increasing the offset, but at the detriment of the ultimate anchor capacity. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.009

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

Public ISBD [article]  in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 837 –846 Titre : Modelling the axial soil resistance on deep-water pipelines Type de document : texte imprimé Auteurs : M. F. Randolph, Auteur ; D. J. White, Auteur ; Y. Yan, Auteur Année de publication : 2012 Article en page(s) : pp. 837 –846 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Friction  Theoretical  analysis  Pipelines  Offshore  engineering Résumé : Axial pipe–soil resistance is an important aspect of deep-water pipeline design, since it influences the longitudinal and lateral buckling responses under thermally induced expansion and contraction of the pipeline. Experimental evidence has shown that the axial resistance, expressed as a proportion of the submerged pipeline weight, can vary by an order of magnitude, depending on the rate of axial movement and cumulative time. This paper provides a theoretical framework for assessing the magnitude of axial friction. The framework is developed within a critical-state context using effective stresses, applicable to any degree of drainage in the soil, quantifying the magnitude and duration of excess pore pressures generated near the pipe/soil interface. Two other aspects of behaviour are added to match the observed velocity dependence of axial resistance: (a) a damage term, leading to contractive volumetric strain at the interface; and (b) strain-rate dependence of the mobilised soil strength. Analytical expressions are derived that capture the above features of the response. The resulting variations of normalised frictional resistance with time and velocity are then shown to match experimental data from interface shear-box tests, representing a planar idealisation of the same behaviour, and from model pipe tests. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.010 [article] Modelling the axial soil resistance on deep-water pipelines [texte imprimé] / M. F. Randolph, Auteur ; D. J. White, Auteur ; Y. Yan, Auteur . - 2012 . - pp. 837 –846. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 9 (Septembre 2012) . - pp. 837 –846 Mots-clés : Friction  Theoretical  analysis  Pipelines  Offshore  engineering Résumé : Axial pipe–soil resistance is an important aspect of deep-water pipeline design, since it influences the longitudinal and lateral buckling responses under thermally induced expansion and contraction of the pipeline. Experimental evidence has shown that the axial resistance, expressed as a proportion of the submerged pipeline weight, can vary by an order of magnitude, depending on the rate of axial movement and cumulative time. This paper provides a theoretical framework for assessing the magnitude of axial friction. The framework is developed within a critical-state context using effective stresses, applicable to any degree of drainage in the soil, quantifying the magnitude and duration of excess pore pressures generated near the pipe/soil interface. Two other aspects of behaviour are added to match the observed velocity dependence of axial resistance: (a) a damage term, leading to contractive volumetric strain at the interface; and (b) strain-rate dependence of the mobilised soil strength. Analytical expressions are derived that capture the above features of the response. The resulting variations of normalised frictional resistance with time and velocity are then shown to match experimental data from interface shear-box tests, representing a planar idealisation of the same behaviour, and from model pipe tests. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.12.OG.010

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

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