Documents disponibles écrits par cet auteur

Changes to particle characteristics associated with the compression of sands / F. N. Altuhafi in Géotechnique, Vol. 61 N° 6 (Juin 2011) 

Public ISBD [article]  in Géotechnique > Vol. 61 N° 6 (Juin 2011) . - pp. 459–471 Titre : Changes to particle characteristics associated with the compression of sands Type de document : texte imprimé Auteurs : F. N. Altuhafi, Auteur ; M. R. Coop, Auteur Année de publication : 2011 Article en page(s) : pp. 459–471 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Particle  crushing/crushability  Microscopy  Sands Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : It is commonly accepted that the onset of particle breakage in sands during compression marks the start of yielding. Although particle breakage is strongly associated with the tensile strength of a single soil grain, initial density and initial sample grading have great influence on the probability of particle breakage. This paper examines the effect of initial grading and density on the sample behaviour during one-dimensional compression for three sands with distinct mineralogies. It was found that a unique normal compression line is the outcome of a large amount of breakage in poorly graded samples and that by changing the initial grading to a better graded sample a significant reduction in particle breakage is observed, until for very well-graded samples no significant particle breakage can be measured. At this point a difficulty in defining a unique normal compression line for the sample was found and a transitional behaviour was identified. In addition to particle size, the paper examines the changes to some important particle characteristics such as particle shape and particle surface roughness in an attempt to relate the soil behaviour to the nature of the microscopic particle damage during yielding. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.114 [article] Changes to particle characteristics associated with the compression of sands [texte imprimé] / F. N. Altuhafi, Auteur ; M. R. Coop, Auteur . - 2011 . - pp. 459–471. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 61 N° 6 (Juin 2011) . - pp. 459–471 Mots-clés : Particle  crushing/crushability  Microscopy  Sands Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : It is commonly accepted that the onset of particle breakage in sands during compression marks the start of yielding. Although particle breakage is strongly associated with the tensile strength of a single soil grain, initial density and initial sample grading have great influence on the probability of particle breakage. This paper examines the effect of initial grading and density on the sample behaviour during one-dimensional compression for three sands with distinct mineralogies. It was found that a unique normal compression line is the outcome of a large amount of breakage in poorly graded samples and that by changing the initial grading to a better graded sample a significant reduction in particle breakage is observed, until for very well-graded samples no significant particle breakage can be measured. At this point a difficulty in defining a unique normal compression line for the sample was found and a transitional behaviour was identified. In addition to particle size, the paper examines the changes to some important particle characteristics such as particle shape and particle surface roughness in an attempt to relate the soil behaviour to the nature of the microscopic particle damage during yielding. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.9.p.114

Drained cyclic behaviour of loose Dogs Bay sand / S. Lopez-Querol in Géotechnique, Vol. 62 N° 4 (Avril 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 4 (Avril 2012) . - pp. 281–289 Titre : Drained cyclic behaviour of loose Dogs Bay sand Type de document : texte imprimé Auteurs : S. Lopez-Querol, Auteur ; M. R. Coop, Auteur Année de publication : 2012 Article en page(s) : pp. 281–289 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Calcareous  soils  Compaction  Dynamics  Sands Résumé : The results of drained cyclic triaxial tests performed on Dogs Bay sand (a carbonate sand) are discussed in this paper. For this sand it has been previously demonstrated that the critical state exists and is unique. The relationship between volumetric strains due to cyclic loading and the critical state of this material under monotonic conditions is explored here. Drained cyclic tests on loose samples have been carried out, applying different amplitudes of cyclic loading for samples that generally have initial states on the wet side of critical. The trends of behaviour are summarised, pointing out the relationship between initial state parameter, amplitude of cyclic loading and final change in the state parameter at equilibrium. Experimental evidence is also given to demonstrate that the sand has a memory of the volumetric strain that has previously occurred when different patterns of cyclic loading are consecutively applied and equilibrium has not been reached. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/issue/geot/62/4# [article] Drained cyclic behaviour of loose Dogs Bay sand [texte imprimé] / S. Lopez-Querol, Auteur ; M. R. Coop, Auteur . - 2012 . - pp. 281–289. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 4 (Avril 2012) . - pp. 281–289 Mots-clés : Calcareous  soils  Compaction  Dynamics  Sands Résumé : The results of drained cyclic triaxial tests performed on Dogs Bay sand (a carbonate sand) are discussed in this paper. For this sand it has been previously demonstrated that the critical state exists and is unique. The relationship between volumetric strains due to cyclic loading and the critical state of this material under monotonic conditions is explored here. Drained cyclic tests on loose samples have been carried out, applying different amplitudes of cyclic loading for samples that generally have initial states on the wet side of critical. The trends of behaviour are summarised, pointing out the relationship between initial state parameter, amplitude of cyclic loading and final change in the state parameter at equilibrium. Experimental evidence is also given to demonstrate that the sand has a memory of the volumetric strain that has previously occurred when different patterns of cyclic loading are consecutively applied and equilibrium has not been reached. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/issue/geot/62/4#

Field studies of an instrumented model pile in clay / M. R. Coop in Géotechnique, Vol. 39 N°4 (Decembre 1989) 

Public ISBD [article]  in Géotechnique > Vol. 39 N°4 (Decembre 1989) . - pp. 679 –696 Titre : Field studies of an instrumented model pile in clay Type de document : texte imprimé Auteurs : M. R. Coop, Auteur ; C. P. Wroth, Auteur Année de publication : 2007 Article en page(s) : pp. 679 –696 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Piles  Offshore  geotech-nits  Field  tests  Research  Model  tests Résumé : An instrumented model pile was used to investigate the fundamental behaviour of driven cylindrical steel piles, in clay soils. Data are described from two test-bed sites, one with heavily over-consolidated clay, and one with normally consoli-dated clay. These confirm that a residual shear surface is formed adjacent to the pile shaft during installation. Comparisons with other site investigation data and cavity expansion theoretical predic- tions suggest that stress relief immediately behind the pile tip during installation gives rise to total radial stress and pore pressure measurements on the shaft which are lower than the simple cavity expansion model predicts. However, the data did indicate that the radial effective stress might be successfully predicted. During reconsolidation, the radial effective stress drops initially, followed by a slow recovery, which was insufticient in the two clays investigated for the final value to reach that during installation. On undrained loading, the clay adjacent to the pile did not reach a critical state as many current theories assume, as failure occurred on the residual surface created during installation. The generation of negative excess pore pressures on the shear surface during undrained loading caused an increase in the radial effective stress. In the normally consolidated clay this was solely responsible for the large set-up of pile shaft capac-ity by comparison with that during installation. The same capacity increase may not be seen in these clays if loading were drained. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.1989.39.4.679 [article] Field studies of an instrumented model pile in clay [texte imprimé] / M. R. Coop, Auteur ; C. P. Wroth, Auteur . - 2007 . - pp. 679 –696. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 39 N°4 (Decembre 1989) . - pp. 679 –696 Mots-clés : Piles  Offshore  geotech-nits  Field  tests  Research  Model  tests Résumé : An instrumented model pile was used to investigate the fundamental behaviour of driven cylindrical steel piles, in clay soils. Data are described from two test-bed sites, one with heavily over-consolidated clay, and one with normally consoli-dated clay. These confirm that a residual shear surface is formed adjacent to the pile shaft during installation. Comparisons with other site investigation data and cavity expansion theoretical predic- tions suggest that stress relief immediately behind the pile tip during installation gives rise to total radial stress and pore pressure measurements on the shaft which are lower than the simple cavity expansion model predicts. However, the data did indicate that the radial effective stress might be successfully predicted. During reconsolidation, the radial effective stress drops initially, followed by a slow recovery, which was insufticient in the two clays investigated for the final value to reach that during installation. On undrained loading, the clay adjacent to the pile did not reach a critical state as many current theories assume, as failure occurred on the residual surface created during installation. The generation of negative excess pore pressures on the shear surface during undrained loading caused an increase in the radial effective stress. In the normally consolidated clay this was solely responsible for the large set-up of pile shaft capac-ity by comparison with that during installation. The same capacity increase may not be seen in these clays if loading were drained. ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/article/10.1680/geot.1989.39.4.679

On the role of bond breakage due to unloading in the behaviour of weak sandstones / G. Alvarado in Géotechnique, Vol. 62 N° 4 (Avril 2012) 

Public ISBD [article]  in Géotechnique > Vol. 62 N° 4 (Avril 2012) . - pp. 303–316 Titre : On the role of bond breakage due to unloading in the behaviour of weak sandstones Type de document : texte imprimé Auteurs : G. Alvarado, Auteur ; M. R. Coop, Auteur ; S. Willson, Auteur Année de publication : 2012 Article en page(s) : pp. 303–316 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Fabric/structure  of  soils  Laboratory  tests  Rocks/rock  mechanics  Sands  Soft  rocks  Stiffness Résumé : A laboratory investigation was made of the effects of isotropic unloading on the mechanical behaviour of cemented sandstones, modelling in a simple way the influence of sampling on hydrocarbon reservoir sandstones that have been cemented at depth. Artificial samples of sandstone were created by allowing a cement to hydrate while a sand sample was under a high confining stress in a triaxial apparatus. Comparisons were then made between the behaviour of samples that had been unloaded to zero confining stress with that of samples tested at stress levels around that during cementing. It was found that the isotropic unloading damaged the cement, which had a significant effect on the small-strain and yielding behaviour but not on the strength and large-strain behaviour. Comparisons were also made with tests on natural samples of reservoir and analogue sandstones, and it was found that the artificial sandstone had reproduced the key elements of their behaviour. The intrinsic properties of all of the sandstones tested were found to be similar, although there were significant differences in the peak strengths and gross yielding envelopes. Cement content was found not to be the sole factor that influenced the peak and gross yield envelopes, and significant anisotropy was also revealed in one sandstone. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/issue/geot/62/4# [article] On the role of bond breakage due to unloading in the behaviour of weak sandstones [texte imprimé] / G. Alvarado, Auteur ; M. R. Coop, Auteur ; S. Willson, Auteur . - 2012 . - pp. 303–316. Génie Civil Langues : Anglais (eng) in Géotechnique > Vol. 62 N° 4 (Avril 2012) . - pp. 303–316 Mots-clés : Fabric/structure  of  soils  Laboratory  tests  Rocks/rock  mechanics  Sands  Soft  rocks  Stiffness Résumé : A laboratory investigation was made of the effects of isotropic unloading on the mechanical behaviour of cemented sandstones, modelling in a simple way the influence of sampling on hydrocarbon reservoir sandstones that have been cemented at depth. Artificial samples of sandstone were created by allowing a cement to hydrate while a sand sample was under a high confining stress in a triaxial apparatus. Comparisons were then made between the behaviour of samples that had been unloaded to zero confining stress with that of samples tested at stress levels around that during cementing. It was found that the isotropic unloading damaged the cement, which had a significant effect on the small-strain and yielding behaviour but not on the strength and large-strain behaviour. Comparisons were also made with tests on natural samples of reservoir and analogue sandstones, and it was found that the artificial sandstone had reproduced the key elements of their behaviour. The intrinsic properties of all of the sandstones tested were found to be similar, although there were significant differences in the peak strengths and gross yielding envelopes. Cement content was found not to be the sole factor that influenced the peak and gross yield envelopes, and significant anisotropy was also revealed in one sandstone. DEWEY : 624.15 ISSN : 0016-8505 En ligne : http://www.icevirtuallibrary.com/content/issue/geot/62/4#