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

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

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

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

Effects of water content and particle crushing on the shear behaviour of an infilled-joint soil / Y. Zhao in Géotechnique, Vol. 62 N° 12 (Décembre 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 12 (Décembre 2012) . - pp. 1133 –1137 Titre : Effects of water content and particle crushing on the shear behaviour of an infilled-joint soil Type de document : texte imprimé Auteurs : Y. Zhao, Auteur ; H. Zhou, Auteur ; X. T. Feng, Auteur Année de publication : 2012 Article en page(s) : pp. 1133 –1137 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Laboratory  tests  Suction  Particle  crushing/crushability  Shear  strength Résumé : Ring shear tests were carried out on a compacted low-plasticity infilled-joint soil from Beihetan site in China. Different initial water contents (5·0, 9·0 and 13·5%) were considered. It was observed that the failure envelope is linear for the peak deviator stress but highly non-linear for the residual deviator stress in the range of high normal stresses (higher than 400 kPa), evidencing the particle crushing effect on the residual strength. Furthermore, this particle crushing effect was dependent on water content: the residual friction angle is larger at higher water content. Further grain size analysis was performed on the portion taken in the zone of shear band after each test, and changes of the fractions of 75 μm and 2 μm were compared for different water contents. The results indicate clearly that the effect of water content on particle crushing depends on particle size. For large particles (> 75 μm), water content increase enhances the particle crushing by the fracture mechanism. On the contrary, for smaller particles (< 2 μm), water content increase reduces the particle crushing by the mechanism of attrition or abrasion. Deeper analysis of the effect of the ratio of the final to initial fraction of soil with particle size less than 2 μm, S2, on the shear strength suggests that the effect of particle crushing on the residual shear strength is mainly through the production of extra clay-size particles (< 2 μm). ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.11.P.060 [article] Effects of water content and particle crushing on the shear behaviour of an infilled-joint soil [texte imprimé] / Y. Zhao, Auteur ; H. Zhou, Auteur ; X. T. Feng, Auteur . - 2012 . - pp. 1133 –1137. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 12 (Décembre 2012) . - pp. 1133 –1137 Mots-clés : Laboratory  tests  Suction  Particle  crushing/crushability  Shear  strength Résumé : Ring shear tests were carried out on a compacted low-plasticity infilled-joint soil from Beihetan site in China. Different initial water contents (5·0, 9·0 and 13·5%) were considered. It was observed that the failure envelope is linear for the peak deviator stress but highly non-linear for the residual deviator stress in the range of high normal stresses (higher than 400 kPa), evidencing the particle crushing effect on the residual strength. Furthermore, this particle crushing effect was dependent on water content: the residual friction angle is larger at higher water content. Further grain size analysis was performed on the portion taken in the zone of shear band after each test, and changes of the fractions of 75 μm and 2 μm were compared for different water contents. The results indicate clearly that the effect of water content on particle crushing depends on particle size. For large particles (> 75 μm), water content increase enhances the particle crushing by the fracture mechanism. On the contrary, for smaller particles (< 2 μm), water content increase reduces the particle crushing by the mechanism of attrition or abrasion. Deeper analysis of the effect of the ratio of the final to initial fraction of soil with particle size less than 2 μm, S2, on the shear strength suggests that the effect of particle crushing on the residual shear strength is mainly through the production of extra clay-size particles (< 2 μm). ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.11.P.060