Dépouillements

The settlement performance of stone column foundations / J. A. Black in Géotechnique, Vol. 61 N° 11 (Novembre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 909-922 Titre : The settlement performance of stone column foundations Type de document : texte imprimé Auteurs : J. A. Black, Auteur ; V. Sivakumar, Auteur ; A. Bell, Auteur Année de publication : 2011 Article en page(s) : pp. 909-922 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Ground  improvement  Model  tests  Settlement  Reinforced  soils  soil/structure  interaction  Footings/foundations Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Vibrated stone columns are frequently used as a method of reinforcing soft ground as they provide increased bearing capacity and reduce foundation settlements. Their performance in relation to bearing capacity is well documented, but there is also a need for enhanced understanding of their settlement characteristics, particularly in relation to small-group configurations. This paper presents results obtained from physical model tests on triaxial specimens 300 mm in diameter and 400 mm high. Parameters investigated include column length to diameter ratio, area replacement ratio and single/group configuration. The findings of the work are as follows. The design is flexible: settlement can equally be controlled using short columns at relatively high area replacement ratios, or longer columns at smaller area replacement ratios. An optimum area replacement ratio of 30–40% exists for the control of settlement. The settlement performance of a small column group is highly influenced by inter-column and footing interaction effects. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.014 [article] The settlement performance of stone column foundations [texte imprimé] / J. A. Black, Auteur ; V. Sivakumar, Auteur ; A. Bell, Auteur . - 2011 . - pp. 909-922. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 909-922 Mots-clés : Ground  improvement  Model  tests  Settlement  Reinforced  soils  soil/structure  interaction  Footings/foundations Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Vibrated stone columns are frequently used as a method of reinforcing soft ground as they provide increased bearing capacity and reduce foundation settlements. Their performance in relation to bearing capacity is well documented, but there is also a need for enhanced understanding of their settlement characteristics, particularly in relation to small-group configurations. This paper presents results obtained from physical model tests on triaxial specimens 300 mm in diameter and 400 mm high. Parameters investigated include column length to diameter ratio, area replacement ratio and single/group configuration. The findings of the work are as follows. The design is flexible: settlement can equally be controlled using short columns at relatively high area replacement ratios, or longer columns at smaller area replacement ratios. An optimum area replacement ratio of 30–40% exists for the control of settlement. The settlement performance of a small column group is highly influenced by inter-column and footing interaction effects. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.014

An exercise on slope stability and perfect elastoplasticity / C. Di Prisco in Géotechnique, Vol. 61 N° 11 (Novembre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 923-934 Titre : An exercise on slope stability and perfect elastoplasticity Type de document : texte imprimé Auteurs : C. Di Prisco, Auteur ; F. Pisano, Auteur Année de publication : 2011 Article en page(s) : pp. 923-934 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Strain  localisation  Theoretical  analysis  Slopes  Liquefaction  Plasticity  Failure Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : In this paper the stability of an infinitely long granular slope is addressed in the framework of small-strain perfect elastoplasticity. The problem is approached by discussing the condition of strain localisation and, through a reinterpretation of the concept of ‘angle of natural repose', a modified strategy for evaluating the slope safety factor is introduced. The angle of natural repose is demonstrated to differ substantially from the material internal friction angle (as this can be determined from standard triaxial tests). The role of non-associativeness is critically discussed and simple shear stress paths are numerically simulated: pseudo-hardening and pseudo-softening regimes are described. The influence of the loading history on the overall ductility/brittleness of the system mechanical response is analysed. To stress the dependency of the angle of natural repose on the material ductility/brittleness, additional simple shear numerical results are illustrated for the case of a strain-softening constitutive relationship. Finally, the stability of the stratum under undrained conditions is critically tackled with reference to the phenomenon of static liquefaction of loose sands. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.040 [article] An exercise on slope stability and perfect elastoplasticity [texte imprimé] / C. Di Prisco, Auteur ; F. Pisano, Auteur . - 2011 . - pp. 923-934. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 923-934 Mots-clés : Strain  localisation  Theoretical  analysis  Slopes  Liquefaction  Plasticity  Failure Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : In this paper the stability of an infinitely long granular slope is addressed in the framework of small-strain perfect elastoplasticity. The problem is approached by discussing the condition of strain localisation and, through a reinterpretation of the concept of ‘angle of natural repose', a modified strategy for evaluating the slope safety factor is introduced. The angle of natural repose is demonstrated to differ substantially from the material internal friction angle (as this can be determined from standard triaxial tests). The role of non-associativeness is critically discussed and simple shear stress paths are numerically simulated: pseudo-hardening and pseudo-softening regimes are described. The influence of the loading history on the overall ductility/brittleness of the system mechanical response is analysed. To stress the dependency of the angle of natural repose on the material ductility/brittleness, additional simple shear numerical results are illustrated for the case of a strain-softening constitutive relationship. Finally, the stability of the stratum under undrained conditions is critically tackled with reference to the phenomenon of static liquefaction of loose sands. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.040

Influence of grading on the mechanical behaviour of Stava tailings / A. Carrera in Géotechnique, Vol. 61 N° 11 (Novembre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 935-946 Titre : Influence of grading on the mechanical behaviour of Stava tailings Type de document : texte imprimé Auteurs : A. Carrera, Auteur ; M. Coop, Auteur ; R. Lancellotta, Auteur Année de publication : 2011 Article en page(s) : pp. 935-946 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Dams  Liquefaction  Sands  Compressibility  Laboratory  tests  Silts Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Tailings dams can be fragile structures and too often they are subject to liquefaction. The material they are composed of is rather peculiar, having a man-made origin, and their behaviour is still not very well understood. The soil from the Stava tailings dams, structures that were subject to liquefaction in 1985 causing extensive destruction, was investigated in this study as an example of tailings. Two main aspects of their behaviour have been examined: the influence of the percentage of silt and sand that compose the soil on its mechanical behaviour, and the susceptibility to liquefaction, analysing the behaviour within a critical state framework. In this paper it is shown that, as the quantity of silt increases, the slope and intercept of the normal compression line and critical state line at higher pressures decrease until an inversion of behaviour is observed, while at lower stress levels the critical state line changes its position but not its slope. This means that the effect of adding silt on the critical state line location at low stresses is disconnected from that at high stresses. The analysis of liquefaction within a critical state framework was found to provide a simple explanation for the patterns of behaviour that are typical of static liquefaction. Three classes of behaviour related to the current void ratio and stress state of the soil were identified. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.009 [article] Influence of grading on the mechanical behaviour of Stava tailings [texte imprimé] / A. Carrera, Auteur ; M. Coop, Auteur ; R. Lancellotta, Auteur . - 2011 . - pp. 935-946. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 935-946 Mots-clés : Dams  Liquefaction  Sands  Compressibility  Laboratory  tests  Silts Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Tailings dams can be fragile structures and too often they are subject to liquefaction. The material they are composed of is rather peculiar, having a man-made origin, and their behaviour is still not very well understood. The soil from the Stava tailings dams, structures that were subject to liquefaction in 1985 causing extensive destruction, was investigated in this study as an example of tailings. Two main aspects of their behaviour have been examined: the influence of the percentage of silt and sand that compose the soil on its mechanical behaviour, and the susceptibility to liquefaction, analysing the behaviour within a critical state framework. In this paper it is shown that, as the quantity of silt increases, the slope and intercept of the normal compression line and critical state line at higher pressures decrease until an inversion of behaviour is observed, while at lower stress levels the critical state line changes its position but not its slope. This means that the effect of adding silt on the critical state line location at low stresses is disconnected from that at high stresses. The analysis of liquefaction within a critical state framework was found to provide a simple explanation for the patterns of behaviour that are typical of static liquefaction. Three classes of behaviour related to the current void ratio and stress state of the soil were identified. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.009

Numerical simulation of pushover tests on a model jack-up platform on clay / G. Vlahos in Géotechnique, Vol. 61 N° 11 (Novembre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 947-960 Titre : Numerical simulation of pushover tests on a model jack-up platform on clay Type de document : texte imprimé Auteurs : G. Vlahos, Auteur ; M. J. Cassidy, Auteur ; C. M. Martin, Auteur Année de publication : 2011 Article en page(s) : pp. 947-960 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Offshore  engineering  Plasticity  Soil–structure  interaction  Numerical  modelling  Model  tests  Footings/foundations  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper assesses a method for predicting the ultimate capacity and failure mode of a model jack-up platform subjected to monotonic pushover tests on soft clay. Separate structural and geotechnical analyses are incapable of making such predictions, so in this work integrated structural/geotechnical simulations are evaluated against detailed experimental pushover data. The commercial finite-element program Abaqus is used, with standard beam elements representing the jack-up structure and a user-defined element describing the behaviour of each spudcan footing by means of a force-resultant plasticity model. This model takes a macro-element approach by expressing the foundation behaviour purely in terms of the loads on the spudcan and the corresponding displacements. Although the model has proven ability to simulate the single-footing experiments from which it was derived, the load paths experienced by the spudcans of a three-legged jack-up are significantly different. To investigate this, numerical simulations of three experimental pushover tests on a 1:250 scale model jack-up have been performed. The tests represent jack-ups with different leg lengths and load orientations. The integrated numerical modelling approach successfully predicts three different failure modes, although the predictions of ultimate pushover capacity are consistently conservative. Because previously published parameters were used for the foundation model, these predictions demonstrate the versatility of the spudcan model in the context of a multi-footing structure, and confirm the effectiveness of the integrated analysis technique. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.114 [article] Numerical simulation of pushover tests on a model jack-up platform on clay [texte imprimé] / G. Vlahos, Auteur ; M. J. Cassidy, Auteur ; C. M. Martin, Auteur . - 2011 . - pp. 947-960. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 947-960 Mots-clés : Offshore  engineering  Plasticity  Soil–structure  interaction  Numerical  modelling  Model  tests  Footings/foundations  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper assesses a method for predicting the ultimate capacity and failure mode of a model jack-up platform subjected to monotonic pushover tests on soft clay. Separate structural and geotechnical analyses are incapable of making such predictions, so in this work integrated structural/geotechnical simulations are evaluated against detailed experimental pushover data. The commercial finite-element program Abaqus is used, with standard beam elements representing the jack-up structure and a user-defined element describing the behaviour of each spudcan footing by means of a force-resultant plasticity model. This model takes a macro-element approach by expressing the foundation behaviour purely in terms of the loads on the spudcan and the corresponding displacements. Although the model has proven ability to simulate the single-footing experiments from which it was derived, the load paths experienced by the spudcans of a three-legged jack-up are significantly different. To investigate this, numerical simulations of three experimental pushover tests on a 1:250 scale model jack-up have been performed. The tests represent jack-ups with different leg lengths and load orientations. The integrated numerical modelling approach successfully predicts three different failure modes, although the predictions of ultimate pushover capacity are consistently conservative. Because previously published parameters were used for the foundation model, these predictions demonstrate the versatility of the spudcan model in the context of a multi-footing structure, and confirm the effectiveness of the integrated analysis technique. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.114

Desiccation cracks in saturated fine-grained soils: particle-level phenomena and effective-stress analysis / H. Shin in Géotechnique, Vol. 61 N° 11 (Novembre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 961-972 Titre : Desiccation cracks in saturated fine-grained soils: particle-level phenomena and effective-stress analysis Type de document : texte imprimé Auteurs : H. Shin, Auteur ; J. C. Santamarina, Auteur Année de publication : 2011 Article en page(s) : pp. 961-972 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Failure  Clays  Suction  Theoretical  analysis Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The formation of desiccation cracks in soils is often interpreted in terms of tensile strength. However, this mechanistic model disregards the cohesionless, effective-stress-dependent frictional behaviour of fine-grained soils. An alternative theory is explored using analyses, numerical simulations based on an effective-stress formulation, and experiments monitored using high-resolution time-lapsed photography. Results show that desiccation cracks in fine-grained sediments initiate as the air–water interface invades the saturated medium, driven by the increase in suction. Thereafter, the interfacial membrane causes an increase in the local void ratio at the tip, the air-entry value decreases, the air–water interface advances into the tip and the crack grows. The effective stress remains in compression everywhere in the soil mass, including at the tip of the desiccation crack. This crack-growing mechanism can explain various observations related to desiccation crack formation in fine-grained soils, including the effects of pore fluid salt concentration, slower crack propagation velocity and right angle realignment while approaching a pre-existing crack, and the apparent strength and failure mode observed in fine-grained soils subjected to tension. Additional research is required to develop a complementary phenomenological model for desiccation crack formation in coarse-grained sediments. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.012 [article] Desiccation cracks in saturated fine-grained soils: particle-level phenomena and effective-stress analysis [texte imprimé] / H. Shin, Auteur ; J. C. Santamarina, Auteur . - 2011 . - pp. 961-972. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 961-972 Mots-clés : Failure  Clays  Suction  Theoretical  analysis Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The formation of desiccation cracks in soils is often interpreted in terms of tensile strength. However, this mechanistic model disregards the cohesionless, effective-stress-dependent frictional behaviour of fine-grained soils. An alternative theory is explored using analyses, numerical simulations based on an effective-stress formulation, and experiments monitored using high-resolution time-lapsed photography. Results show that desiccation cracks in fine-grained sediments initiate as the air–water interface invades the saturated medium, driven by the increase in suction. Thereafter, the interfacial membrane causes an increase in the local void ratio at the tip, the air-entry value decreases, the air–water interface advances into the tip and the crack grows. The effective stress remains in compression everywhere in the soil mass, including at the tip of the desiccation crack. This crack-growing mechanism can explain various observations related to desiccation crack formation in fine-grained soils, including the effects of pore fluid salt concentration, slower crack propagation velocity and right angle realignment while approaching a pre-existing crack, and the apparent strength and failure mode observed in fine-grained soils subjected to tension. Additional research is required to develop a complementary phenomenological model for desiccation crack formation in coarse-grained sediments. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.8.p.012

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

Public ISBD [article]  in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 973-981 Titre : Effect of shaft on resistance of a ball penetrometer Type de document : texte imprimé Auteurs : H. Zhou, Auteur ; M. F. Randolph, Auteur Année de publication : 2011 Article en page(s) : pp. 973-981 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Clays  Numerical  modelling  In  situ  testing  Shear  strength Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The influence of the shaft on the resistance of a ball penetrometer was examined using a large deformation finite-element approach. A range of ball–shaft diameter ratios between infinitely large (no shaft) to 1 were examined in terms of resistance during monotonic penetration and extraction. It was found that the steady-state resistance decreased with decreasing ball–shaft diameter ratio, and that greater displacement (as a proportion of the shaft diameter) was required to reach a steady state. The finite-element results were matched closely using an upper bound approach, treating the shaft and outer part of the ball separately. It was also found that the rigidity index of the soil affected the penetration resistance of the shafted ball, but the influence was much less than for a cone penetrometer, being essentially proportional to the shaft–ball area ratio. Finally cyclic penetration and extraction tests were modelled comparing results for the no-shaft ball and a shafted ball with ball–shaft diameter ratios of 2 and 3. The presence of the shaft was found to have minimal influence on the resistance and cyclic degradation curves, although at the later stage of cycling the penetration resistance becomes greater than the extraction resistance. The corresponding resistance ratio of extraction to penetration for each cycle reduces with decreasing ball–shaft diameter ratio and increasing soil sensitivity. In terms of the change in mean total stress, however, the presence of the shaft introduces a pronounced gradient with respect to displacement during cyclic penetration and extraction, while increasing the changes in mean stress significantly during initial penetration. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.062 [article] Effect of shaft on resistance of a ball penetrometer [texte imprimé] / H. Zhou, Auteur ; M. F. Randolph, Auteur . - 2011 . - pp. 973-981. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 973-981 Mots-clés : Clays  Numerical  modelling  In  situ  testing  Shear  strength Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : The influence of the shaft on the resistance of a ball penetrometer was examined using a large deformation finite-element approach. A range of ball–shaft diameter ratios between infinitely large (no shaft) to 1 were examined in terms of resistance during monotonic penetration and extraction. It was found that the steady-state resistance decreased with decreasing ball–shaft diameter ratio, and that greater displacement (as a proportion of the shaft diameter) was required to reach a steady state. The finite-element results were matched closely using an upper bound approach, treating the shaft and outer part of the ball separately. It was also found that the rigidity index of the soil affected the penetration resistance of the shafted ball, but the influence was much less than for a cone penetrometer, being essentially proportional to the shaft–ball area ratio. Finally cyclic penetration and extraction tests were modelled comparing results for the no-shaft ball and a shafted ball with ball–shaft diameter ratios of 2 and 3. The presence of the shaft was found to have minimal influence on the resistance and cyclic degradation curves, although at the later stage of cycling the penetration resistance becomes greater than the extraction resistance. The corresponding resistance ratio of extraction to penetration for each cycle reduces with decreasing ball–shaft diameter ratio and increasing soil sensitivity. In terms of the change in mean total stress, however, the presence of the shaft introduces a pronounced gradient with respect to displacement during cyclic penetration and extraction, while increasing the changes in mean stress significantly during initial penetration. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.062

Simulations of cyclic shearing of sand at low effective stress / C. M. Sands in Géotechnique, Vol. 61 N° 11 (Novembre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 983-992 Titre : Simulations of cyclic shearing of sand at low effective stress Type de document : texte imprimé Auteurs : C. M. Sands, Auteur ; H. W. Chandler, Auteur Année de publication : 2011 Article en page(s) : pp. 983-992 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Constitutive  relations  Earthquakes  Sands  Torsion  Repeated  loading  Friction Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper presents a very simple soil model of reduced dimensionality, that, using only two adjustable parameters, captures all the essential features of a set of six undrained cyclic torsional shear tests carried out on Toyoura sand by Oka and co-workers. The same values for all the model parameters (all but two of which are obtained from published data) are used for all six tests and very good agreement between the experimental test results and the simulations is achieved. Simulations of drained tests are also presented. The model uses a parameter that stores the recent strain history of the soil and that the authors show can be related to Houlsby's anisotropy parameter. The relationship between the volume and shear strain increments contains two terms. The first term simulates continual compaction while the second can predict additional compaction or dilatancy, depending on the direction of the shear strain increment. These two terms cancel each other out during continuous deformation at the critical state, but reinforce each other on reversal to predict the rapid densification observed experimentally. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.060 [article] Simulations of cyclic shearing of sand at low effective stress [texte imprimé] / C. M. Sands, Auteur ; H. W. Chandler, Auteur . - 2011 . - pp. 983-992. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 983-992 Mots-clés : Constitutive  relations  Earthquakes  Sands  Torsion  Repeated  loading  Friction Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper presents a very simple soil model of reduced dimensionality, that, using only two adjustable parameters, captures all the essential features of a set of six undrained cyclic torsional shear tests carried out on Toyoura sand by Oka and co-workers. The same values for all the model parameters (all but two of which are obtained from published data) are used for all six tests and very good agreement between the experimental test results and the simulations is achieved. Simulations of drained tests are also presented. The model uses a parameter that stores the recent strain history of the soil and that the authors show can be related to Houlsby's anisotropy parameter. The relationship between the volume and shear strain increments contains two terms. The first term simulates continual compaction while the second can predict additional compaction or dilatancy, depending on the direction of the shear strain increment. These two terms cancel each other out during continuous deformation at the critical state, but reinforce each other on reversal to predict the rapid densification observed experimentally. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.060

Physical modelling of deformations around piling augers in clay / C. C. Hird in Géotechnique, Vol. 61 N° 11 (Novembre 2010) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 993-999 Titre : Physical modelling of deformations around piling augers in clay Type de document : texte imprimé Auteurs : C. C. Hird, Auteur ; Q. Ni, Auteur ; Guymer, I., Auteur Année de publication : 2011 Article en page(s) : pp. 993-999 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Model  tests  Deformation  Piles  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Small-scale model tests are reported in which miniature augers were installed in beds of transparent synthetic soil simulating clay. As the auger advanced, the movement of reflective particles seeded into the soil and illuminated by laser light was recorded photographically. The displacement field in a vertical plane aligned with the auger axis was then determined using particle image velocimetry. The pattern of deformation of the soil around an auger of the type used to form a cast-in-situ screw pile was similar to that around a cylindrical straight-sided pushed pile. Deformations around an auger of the type used to form a rotary displacement pile depended on the rotation speed of the auger and the extent to which the flights carried soil upwards away from the tip. Lateral displacements in the model tests exhibited roughly similar trends to those observed in the field. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.t.028 [article] Physical modelling of deformations around piling augers in clay [texte imprimé] / C. C. Hird, Auteur ; Q. Ni, Auteur ; Guymer, I., Auteur . - 2011 . - pp. 993-999. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 11 (Novembre 2010) . - pp. 993-999 Mots-clés : Model  tests  Deformation  Piles  Clays Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Small-scale model tests are reported in which miniature augers were installed in beds of transparent synthetic soil simulating clay. As the auger advanced, the movement of reflective particles seeded into the soil and illuminated by laser light was recorded photographically. The displacement field in a vertical plane aligned with the auger axis was then determined using particle image velocimetry. The pattern of deformation of the soil around an auger of the type used to form a cast-in-situ screw pile was similar to that around a cylindrical straight-sided pushed pile. Deformations around an auger of the type used to form a rotary displacement pile depended on the rotation speed of the auger and the extent to which the flights carried soil upwards away from the tip. Lateral displacements in the model tests exhibited roughly similar trends to those observed in the field. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.t.028

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