Dépouillements

Stiffness at small strain: research and practice / C. R. I. Clayton in Géotechnique, Vol. LXI N° 1 (Janvier 2011) 

Public ISBD [article]  in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 5–37 Titre : Stiffness at small strain: research and practice Type de document : texte imprimé Auteurs : C. R. I. Clayton, Auteur Année de publication : 2011 Article en page(s) : pp. 5–37 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Ground  movements  Geophysics  Laboratory  equipment  Elasticity  Laboratory  tests  Stiffness  In  situ  testing  Deformation  Anisotropy Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper provides the background to the 50th Rankine Lecture. It considers the growth in emphasis of the prediction of ground displacements during design in the past two decades of the 20th century, as a result of the lessons learnt from field observations. The historical development of the theory of elasticity is then described, as are the constitutive frameworks within which it has been proposed that geotechnical predictions of deformation should be carried out. Factors affecting the stiffness of soils and weak rocks are reviewed, and the results of a numerical experiment, assessing the impact of a number of stiffness parameters on the displacements around a retaining structure, are described. Some field and laboratory methods of obtaining stiffness parameters are considered and critically discussed, and the paper concludes with a suggested strategy for the measurement and integration of stiffness data, and the developments necessary to improve the existing state of the art. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.2011.61.1.5 [article] Stiffness at small strain: research and practice [texte imprimé] / C. R. I. Clayton, Auteur . - 2011 . - pp. 5–37. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 5–37 Mots-clés : Ground  movements  Geophysics  Laboratory  equipment  Elasticity  Laboratory  tests  Stiffness  In  situ  testing  Deformation  Anisotropy Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper provides the background to the 50th Rankine Lecture. It considers the growth in emphasis of the prediction of ground displacements during design in the past two decades of the 20th century, as a result of the lessons learnt from field observations. The historical development of the theory of elasticity is then described, as are the constitutive frameworks within which it has been proposed that geotechnical predictions of deformation should be carried out. Factors affecting the stiffness of soils and weak rocks are reviewed, and the results of a numerical experiment, assessing the impact of a number of stiffness parameters on the displacements around a retaining structure, are described. Some field and laboratory methods of obtaining stiffness parameters are considered and critically discussed, and the paper concludes with a suggested strategy for the measurement and integration of stiffness data, and the developments necessary to improve the existing state of the art. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.2011.61.1.5

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

Public ISBD [article]  in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 39-57 Titre : Modelling the dynamic embedment of seabed pipelines Type de document : texte imprimé Auteurs : C. Y. Cheuk, Auteur ; D. J. White, Auteur Année de publication : 2011 Article en page(s) : pp. 39-57 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Plasticity  Clays  Failure  Theoretical  analysis  Centrifuge  modelling  Offshore  engineering Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The as-laid embedment of a seabed pipeline is an important design parameter. As a pipe is laid on the seabed it oscillates, owing to vessel motion and hydrodynamic loading of the hanging pipe. This movement significantly increases the pipe embedment beyond the theoretical value related to the static pipe weight, even when corrected for any stress concentration caused by the hanging catenary. Dynamic lay effects are either ignored in practice, or are accounted for by scaling up the static embedment by an empirical factor, leading to significant uncertainty in this important design parameter. A series of centrifuge model tests has been conducted using two clays – kaolin and a high-plasticity natural clay – to simulate the dynamic embedment process. The results indicate that only a few cycles of small-amplitude oscillation (±0·05D) are required to double or triple the pipe embedment, owing to the combined effect of lateral ploughing and soil softening. In these experiments the pipe embedment increased to up to eight times the static embedment after 100 cycles of motion, which represents a typical lay process. A model is proposed for the cycle-by-cycle embedment of a pipeline under a given sequence of small-amplitude oscillations at a given applied vertical force. The trajectory of the pipe movement is assessed using a flow rule derived from plasticity-based yield envelopes. The effect of soil remoulding is explicitly captured by linking the accumulated disturbance to the decay in soil strength. Using input parameters derived from theoretical considerations and T-bar penetrometer tests, the model captures the essential features of the dynamic embedment process. With modest optimisation of the model parameters, the mean discrepancy between the calculated and measured embedment is only 12% for both clays. The ultimate states predicted by this cycle-by-cycle model also provide a rough estimate of the maximum pipe embedment for fully remoulded conditions, which include some degree of water entrainment caused by the lay process, evident in the optimised parameters. This ultimate embedment is governed by the remoulded soil strength and the pipe weight (augmented by any stress concentration). The amplitude of the cyclic motion affects the rate of softening, and hence the rate of settlement. This model provides a framework for assessing the as-laid embedment of seabed pipelines on a more rigorous basis than current practice. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.148 [article] Modelling the dynamic embedment of seabed pipelines [texte imprimé] / C. Y. Cheuk, Auteur ; D. J. White, Auteur . - 2011 . - pp. 39-57. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 39-57 Mots-clés : Plasticity  Clays  Failure  Theoretical  analysis  Centrifuge  modelling  Offshore  engineering Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The as-laid embedment of a seabed pipeline is an important design parameter. As a pipe is laid on the seabed it oscillates, owing to vessel motion and hydrodynamic loading of the hanging pipe. This movement significantly increases the pipe embedment beyond the theoretical value related to the static pipe weight, even when corrected for any stress concentration caused by the hanging catenary. Dynamic lay effects are either ignored in practice, or are accounted for by scaling up the static embedment by an empirical factor, leading to significant uncertainty in this important design parameter. A series of centrifuge model tests has been conducted using two clays – kaolin and a high-plasticity natural clay – to simulate the dynamic embedment process. The results indicate that only a few cycles of small-amplitude oscillation (±0·05D) are required to double or triple the pipe embedment, owing to the combined effect of lateral ploughing and soil softening. In these experiments the pipe embedment increased to up to eight times the static embedment after 100 cycles of motion, which represents a typical lay process. A model is proposed for the cycle-by-cycle embedment of a pipeline under a given sequence of small-amplitude oscillations at a given applied vertical force. The trajectory of the pipe movement is assessed using a flow rule derived from plasticity-based yield envelopes. The effect of soil remoulding is explicitly captured by linking the accumulated disturbance to the decay in soil strength. Using input parameters derived from theoretical considerations and T-bar penetrometer tests, the model captures the essential features of the dynamic embedment process. With modest optimisation of the model parameters, the mean discrepancy between the calculated and measured embedment is only 12% for both clays. The ultimate states predicted by this cycle-by-cycle model also provide a rough estimate of the maximum pipe embedment for fully remoulded conditions, which include some degree of water entrainment caused by the lay process, evident in the optimised parameters. This ultimate embedment is governed by the remoulded soil strength and the pipe weight (augmented by any stress concentration). The amplitude of the cyclic motion affects the rate of softening, and hence the rate of settlement. This model provides a framework for assessing the as-laid embedment of seabed pipelines on a more rigorous basis than current practice. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.148

Cyclic behaviour and resistance of saturated sand under non-symmetrical loading / J. Yang in Géotechnique, Vol. LXI N° 1 (Janvier 2011) 

Public ISBD [article]  in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 59–73 Titre : Cyclic behaviour and resistance of saturated sand under non-symmetrical loading Type de document : texte imprimé Auteurs : J. Yang, Auteur ; H. Y. Sze, Auteur Année de publication : 2011 Article en page(s) : pp. 59–73 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Shear  strength  Earthquakes  Liquefaction  Laboratory  tests  Failure  Sands Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper reports findings from an experimental study that aimed to investigate the undrained behaviour of sand in non-symmetrical cyclic loading, and to clarify the role of initial static shear in liquefaction resistance. The testing programme, conducted on a standard sand under triaxial conditions, covers a broad range of initial states in terms of relative density, confining stress and initial shear stress ratio (α). Three distinct failure modes have been identified from the tests: flow-type failure, cyclic mobility and plastic strain accumulation. Of these, flow-type failure, characterised by abrupt runaway deformations without any prior warning, is the most critical, and pertains to sand in the loose state. The tests also demonstrate that the presence of initial static shear stress is beneficial to the liquefaction resistance of loose sand at low α levels, but it becomes detrimental at high α levels. In this connection the concept of threshold α is proposed, together with the use of a no-stress-reversal line for better characterisation of the effect of initial static shear. Furthermore, in the conceptual framework of critical state soil mechanics, a fairly good linear relationship has been established between the threshold α and the state parameter ψ that collectively accounts for the initial relative density and mean stress level. This relationship suggests that the threshold α decreases with increasing values of ψ , or with sand becoming looser than the critical state. It is further proposed that the concept of threshold α also applies to sand at high relative density, as long as the confining stress becomes sufficiently high. This proposal leads to a unified and consistent interpretation of the complicated static shear effect. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.019 [article] Cyclic behaviour and resistance of saturated sand under non-symmetrical loading [texte imprimé] / J. Yang, Auteur ; H. Y. Sze, Auteur . - 2011 . - pp. 59–73. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 59–73 Mots-clés : Shear  strength  Earthquakes  Liquefaction  Laboratory  tests  Failure  Sands Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper reports findings from an experimental study that aimed to investigate the undrained behaviour of sand in non-symmetrical cyclic loading, and to clarify the role of initial static shear in liquefaction resistance. The testing programme, conducted on a standard sand under triaxial conditions, covers a broad range of initial states in terms of relative density, confining stress and initial shear stress ratio (α). Three distinct failure modes have been identified from the tests: flow-type failure, cyclic mobility and plastic strain accumulation. Of these, flow-type failure, characterised by abrupt runaway deformations without any prior warning, is the most critical, and pertains to sand in the loose state. The tests also demonstrate that the presence of initial static shear stress is beneficial to the liquefaction resistance of loose sand at low α levels, but it becomes detrimental at high α levels. In this connection the concept of threshold α is proposed, together with the use of a no-stress-reversal line for better characterisation of the effect of initial static shear. Furthermore, in the conceptual framework of critical state soil mechanics, a fairly good linear relationship has been established between the threshold α and the state parameter ψ that collectively accounts for the initial relative density and mean stress level. This relationship suggests that the threshold α decreases with increasing values of ψ , or with sand becoming looser than the critical state. It is further proposed that the concept of threshold α also applies to sand at high relative density, as long as the confining stress becomes sufficiently high. This proposal leads to a unified and consistent interpretation of the complicated static shear effect. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.019

Dilatancy of the interface between a structure and gravelly soil / G. Zhang in Géotechnique, Vol. LXI N° 1 (Janvier 2011) 

Public ISBD [article]  in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 75–84 Titre : Dilatancy of the interface between a structure and gravelly soil Type de document : texte imprimé Auteurs : G. Zhang, Auteur ; L. Wang, Auteur ; J.-M. Zhang, Auteur Année de publication : 2011 Article en page(s) : pp. 75–84 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Gravels  Soil/structure  interaction  Constitutive  relations  Laboratory  tests  Shear  strength Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Dilatancy is one of the key properties of the soil–structure interface. A number of monotonic and cyclic shear tests were analysed to derive the rules and the dilatancy mechanism of the interface between a structure and a gravelly soil; diverse influential factors were considered, such as soil type, roughness of the structure and normal stress. The volumetric change due to the dilatancy consists of a reversible and irreversible dilatancy component, each of which has different mechanisms, different rules and different control factors. The reversible dilatancy component is strongly dependent on the direction of the applied shear after an initial application of shear loading. The irreversible dilatancy component gradually increases owing to the continued application of shear and exhibits a close relationship with the evolution of the physical state. The volumetric change that is due to the dilatancy mainly depends on part of the tangential displacement which corresponds to the deformation of the soil that is constrained by the structure; such a part of the tangential displacement is significantly dependent on the state of the entire tangential displacement, on the normal stress and on the features of both the structure and the soil. The roughness of the structure, the behaviour of the soil and the normal stress have significant effects on the dilatancy behaviour of the interface. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.051 [article] Dilatancy of the interface between a structure and gravelly soil [texte imprimé] / G. Zhang, Auteur ; L. Wang, Auteur ; J.-M. Zhang, Auteur . - 2011 . - pp. 75–84. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. LXI N° 1 (Janvier 2011) . - pp. 75–84 Mots-clés : Gravels  Soil/structure  interaction  Constitutive  relations  Laboratory  tests  Shear  strength Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Dilatancy is one of the key properties of the soil–structure interface. A number of monotonic and cyclic shear tests were analysed to derive the rules and the dilatancy mechanism of the interface between a structure and a gravelly soil; diverse influential factors were considered, such as soil type, roughness of the structure and normal stress. The volumetric change due to the dilatancy consists of a reversible and irreversible dilatancy component, each of which has different mechanisms, different rules and different control factors. The reversible dilatancy component is strongly dependent on the direction of the applied shear after an initial application of shear loading. The irreversible dilatancy component gradually increases owing to the continued application of shear and exhibits a close relationship with the evolution of the physical state. The volumetric change that is due to the dilatancy mainly depends on part of the tangential displacement which corresponds to the deformation of the soil that is constrained by the structure; such a part of the tangential displacement is significantly dependent on the state of the entire tangential displacement, on the normal stress and on the features of both the structure and the soil. The roughness of the structure, the behaviour of the soil and the normal stress have significant effects on the dilatancy behaviour of the interface. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.051

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