Documents disponibles écrits par cet auteur

Geotechnical properties of cemented sands in steep slopes / Brian D. Collins in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 10 (Octobre 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 10 (Octobre 2009) . - pp. 1359–1366 Titre : Geotechnical properties of cemented sands in steep slopes Type de document : texte imprimé Auteurs : Brian D. Collins, Auteur ; Sitar, Nicholas, Auteur Année de publication : 2009 Article en page(s) : pp. 1359–1366 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : SandSoil  cementSlope  stabilityTriaxial  testsCliffsSoil  properties Résumé : An investigation into the geotechnical properties specific to assessing the stability of weakly and moderately cemented sand cliffs is presented. A case study from eroding coastal cliffs located in central California provides both the data and impetus for this study. Herein, weakly cemented sand is defined as having an unconfined compressive strength (UCS) of less than 100 kPa, and moderately cemented sand is defined as having UCS between 100 and 400 kPa. Testing shows that both materials fail in a brittle fashion and can be modeled effectively using linear Mohr-Coulomb strength parameters, although for weakly cemented sands, curvature of the failure envelope is more evident with decreasing friction and increasing cohesion at higher confinement. Triaxial tests performed to simulate the evolving stress state of an eroding cliff, using a reduction in confinement-type stress path, result in an order of magnitude decrease in strain at failure and a more brittle response. Tests aimed at examining the influence of wetting on steep slopes show that a 60% decrease in UCS, a 50% drop in cohesion, and 80% decrease in the tensile strength occurs in moderately cemented sand upon introduction to water. In weakly cemented sands, all compressive, cohesive, and tensile strength is lost upon wetting and saturation. The results indicate that particular attention must be given to the relative level of cementation, the effects of groundwater or surficial seepage, and the small-scale strain response when performing geotechnical slope stability analyses on these materials. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000094 [article] Geotechnical properties of cemented sands in steep slopes [texte imprimé] / Brian D. Collins, Auteur ; Sitar, Nicholas, Auteur . - 2009 . - pp. 1359–1366. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 10 (Octobre 2009) . - pp. 1359–1366 Mots-clés : SandSoil  cementSlope  stabilityTriaxial  testsCliffsSoil  properties Résumé : An investigation into the geotechnical properties specific to assessing the stability of weakly and moderately cemented sand cliffs is presented. A case study from eroding coastal cliffs located in central California provides both the data and impetus for this study. Herein, weakly cemented sand is defined as having an unconfined compressive strength (UCS) of less than 100 kPa, and moderately cemented sand is defined as having UCS between 100 and 400 kPa. Testing shows that both materials fail in a brittle fashion and can be modeled effectively using linear Mohr-Coulomb strength parameters, although for weakly cemented sands, curvature of the failure envelope is more evident with decreasing friction and increasing cohesion at higher confinement. Triaxial tests performed to simulate the evolving stress state of an eroding cliff, using a reduction in confinement-type stress path, result in an order of magnitude decrease in strain at failure and a more brittle response. Tests aimed at examining the influence of wetting on steep slopes show that a 60% decrease in UCS, a 50% drop in cohesion, and 80% decrease in the tensile strength occurs in moderately cemented sand upon introduction to water. In weakly cemented sands, all compressive, cohesive, and tensile strength is lost upon wetting and saturation. The results indicate that particular attention must be given to the relative level of cementation, the effects of groundwater or surficial seepage, and the small-scale strain response when performing geotechnical slope stability analyses on these materials. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000094

Seismic earth pressures on cantilever retaining structures / Linda Al Atik in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 10 (Octobre 2010) . - pp. 1324-1333 Titre : Seismic earth pressures on cantilever retaining structures Type de document : texte imprimé Auteurs : Linda Al Atik, Auteur ; Sitar, Nicholas, Auteur Article en page(s) : pp. 1324-1333 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Retaining  walls  Earth  pressure  Seismic  effects  Earthquakes  Centrifuge  models  Numerical  models  Simulation  Seismic  design  Backfills Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : An experimental and analytical program was designed and conducted to evaluate the magnitude and distribution of seismically induced lateral earth pressures on cantilever retaining structures with dry medium dense sand backfill. Results from two sets of dynamic centrifuge experiments and two-dimensional nonlinear finite-element analyses show that maximum dynamic earth pressures monotonically increase with depth and can be reasonably approximated by a triangular distribution. Moreover, dynamic earth pressures and inertia forces do not act simultaneously on the cantilever retaining walls. As a result, designing cantilever retaining walls for maximum dynamic earth pressure increment and maximum wall inertia, as is the current practice, is overly conservative and does not reflect the true seismic response of the wall-backfill system. The relationship between the seismic earth pressure increment coefficient (DeltaKAE) at the time of maximum overall wall moment and peak ground acceleration obtained from our experiments suggests that seismic earth pressures on cantilever retaining walls can be neglected at accelerations below 0.4 g. This finding is consistent with the observed good seismic performance of conventionally designed cantilever retaining structures. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...] [article] Seismic earth pressures on cantilever retaining structures [texte imprimé] / Linda Al Atik, Auteur ; Sitar, Nicholas, Auteur . - pp. 1324-1333. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 10 (Octobre 2010) . - pp. 1324-1333 Mots-clés : Retaining  walls  Earth  pressure  Seismic  effects  Earthquakes  Centrifuge  models  Numerical  models  Simulation  Seismic  design  Backfills Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : An experimental and analytical program was designed and conducted to evaluate the magnitude and distribution of seismically induced lateral earth pressures on cantilever retaining structures with dry medium dense sand backfill. Results from two sets of dynamic centrifuge experiments and two-dimensional nonlinear finite-element analyses show that maximum dynamic earth pressures monotonically increase with depth and can be reasonably approximated by a triangular distribution. Moreover, dynamic earth pressures and inertia forces do not act simultaneously on the cantilever retaining walls. As a result, designing cantilever retaining walls for maximum dynamic earth pressure increment and maximum wall inertia, as is the current practice, is overly conservative and does not reflect the true seismic response of the wall-backfill system. The relationship between the seismic earth pressure increment coefficient (DeltaKAE) at the time of maximum overall wall moment and peak ground acceleration obtained from our experiments suggests that seismic earth pressures on cantilever retaining walls can be neglected at accelerations below 0.4 g. This finding is consistent with the observed good seismic performance of conventionally designed cantilever retaining structures. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...]

Stability of steep slopes in cemented sands / Brian D. Collins in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 1 (Janvier 2011) . - pp. 27-42 Titre : Stability of steep slopes in cemented sands Type de document : texte imprimé Auteurs : Brian D. Collins, Auteur ; Sitar, Nicholas, Auteur Année de publication : 2011 Article en page(s) : pp. 27-42 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Slope  stability  Cemented  sand  Limiting  equilibrium  Tensile  strength  Lidar  Cliffs  Failure  mode Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : The analysis of steep slope and cliff stability in variably cemented sands poses a significant practical challenge as routine analyses tend to underestimate the actually observed stability of existing slopes. The presented research evaluates how the degree of cementation controls the evolution of steep sand slopes and shows that the detailed slope geometry is important in determining the characteristics of the failure mode, which in turn, guide the selection of an appropriate stability analysis method. Detailed slope-profile cross sections derived from terrestrial lidar surveying of otherwise inaccessible cemented sand cliffs are used to investigate failure modes in weakly cemented [unconfined compressive strength (UCS)<30 kPa] and moderately cemented (30 DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i1/p43_s1?isAuthorized=no [article] Stability of steep slopes in cemented sands [texte imprimé] / Brian D. Collins, Auteur ; Sitar, Nicholas, Auteur . - 2011 . - pp. 27-42. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 1 (Janvier 2011) . - pp. 27-42 Mots-clés : Slope  stability  Cemented  sand  Limiting  equilibrium  Tensile  strength  Lidar  Cliffs  Failure  mode Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : The analysis of steep slope and cliff stability in variably cemented sands poses a significant practical challenge as routine analyses tend to underestimate the actually observed stability of existing slopes. The presented research evaluates how the degree of cementation controls the evolution of steep sand slopes and shows that the detailed slope geometry is important in determining the characteristics of the failure mode, which in turn, guide the selection of an appropriate stability analysis method. Detailed slope-profile cross sections derived from terrestrial lidar surveying of otherwise inaccessible cemented sand cliffs are used to investigate failure modes in weakly cemented [unconfined compressive strength (UCS)<30 kPa] and moderately cemented (30 DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i1/p43_s1?isAuthorized=no

Stability of steep slopes in cemented sands / Brian D. Collins in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 1 (Janvier 2011) . - pp. 43-51 Titre : Stability of steep slopes in cemented sands Type de document : texte imprimé Auteurs : Brian D. Collins, Auteur ; Sitar, Nicholas, Auteur Année de publication : 2011 Article en page(s) : pp. 43-51 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Slope  stability  Cemented  sand  Limiting  equilibrium  Tensile  strength  Lidar  Cliffs  Failure  mode Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : The analysis of steep slope and cliff stability in variably cemented sands poses a significant practical challenge as routine analyses tend to underestimate the actually observed stability of existing slopes. The presented research evaluates how the degree of cementation controls the evolution of steep sand slopes and shows that the detailed slope geometry is important in determining the characteristics of the failure mode, which in turn, guide the selection of an appropriate stability analysis method. Detailed slope-profile cross sections derived from terrestrial lidar surveying of otherwise inaccessible cemented sand cliffs are used to investigate failure modes in weakly cemented [unconfined compressive strength (UCS)<30 kPa] and moderately cemented (30 DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i1/p43_s1?isAuthorized=no [article] Stability of steep slopes in cemented sands [texte imprimé] / Brian D. Collins, Auteur ; Sitar, Nicholas, Auteur . - 2011 . - pp. 43-51. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 1 (Janvier 2011) . - pp. 43-51 Mots-clés : Slope  stability  Cemented  sand  Limiting  equilibrium  Tensile  strength  Lidar  Cliffs  Failure  mode Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : The analysis of steep slope and cliff stability in variably cemented sands poses a significant practical challenge as routine analyses tend to underestimate the actually observed stability of existing slopes. The presented research evaluates how the degree of cementation controls the evolution of steep sand slopes and shows that the detailed slope geometry is important in determining the characteristics of the failure mode, which in turn, guide the selection of an appropriate stability analysis method. Detailed slope-profile cross sections derived from terrestrial lidar surveying of otherwise inaccessible cemented sand cliffs are used to investigate failure modes in weakly cemented [unconfined compressive strength (UCS)<30 kPa] and moderately cemented (30 DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i1/p43_s1?isAuthorized=no

Static and dynamic axial response of drilled piers / Gang Wang in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 12 (Décembre 2011) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1133-1142 Titre : Static and dynamic axial response of drilled piers : I: Field tests Type de document : texte imprimé Auteurs : Gang Wang, Auteur ; Gyimah Kasali, Auteur ; Sitar, Nicholas, Auteur Année de publication : 2012 Article en page(s) : pp. 1133-1142 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Drilled  pier  Dynamic  loading  Axial  load  Field  study Résumé : A prototype pier load test program was performed to study the load-deformation and energy-dissipation characteristics of the response of drilled piers under static and dynamic axial loads. The field tests consisted of six fully instrumented drilled concrete piers 61–76 cm (24–30 in.) in diameter and 5.8–9.1 m (19–30 ft) in length. The piers were constructed on a stiff, sandy clay site adjacent to the University of California, Berkeley campus. A dynamic Fundex pile load test (PLT) was performed on each pier, followed by a static-compression or tension test and a second PLT. The field tests revealed that the stiffness and capacity of a soil-pier system depend significantly on the loading rate. For the type of piers and soil considered in the field test, the increase in dynamic stiffness versus static stiffness is approximately 20–40% at almost all displacement levels. The ultimate dynamic capacity increases approximately 30% compared with the static case. The multiple PLTs conducted on the same drilled pier also indicated that a pier may experience up to 50% stiffness and strength degradation when subjected to full load reversal. The test program showed that the PLT is a fast, innovative method to get useful site-specific information for seismic design of the pier foundation. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i12/p1133_s1?isAuthorized=no [article] Static and dynamic axial response of drilled piers : I: Field tests [texte imprimé] / Gang Wang, Auteur ; Gyimah Kasali, Auteur ; Sitar, Nicholas, Auteur . - 2012 . - pp. 1133-1142. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1133-1142 Mots-clés : Drilled  pier  Dynamic  loading  Axial  load  Field  study Résumé : A prototype pier load test program was performed to study the load-deformation and energy-dissipation characteristics of the response of drilled piers under static and dynamic axial loads. The field tests consisted of six fully instrumented drilled concrete piers 61–76 cm (24–30 in.) in diameter and 5.8–9.1 m (19–30 ft) in length. The piers were constructed on a stiff, sandy clay site adjacent to the University of California, Berkeley campus. A dynamic Fundex pile load test (PLT) was performed on each pier, followed by a static-compression or tension test and a second PLT. The field tests revealed that the stiffness and capacity of a soil-pier system depend significantly on the loading rate. For the type of piers and soil considered in the field test, the increase in dynamic stiffness versus static stiffness is approximately 20–40% at almost all displacement levels. The ultimate dynamic capacity increases approximately 30% compared with the static case. The multiple PLTs conducted on the same drilled pier also indicated that a pier may experience up to 50% stiffness and strength degradation when subjected to full load reversal. The test program showed that the PLT is a fast, innovative method to get useful site-specific information for seismic design of the pier foundation. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i12/p1133_s1?isAuthorized=no

Static and dynamic axial response of drilled piers / Gang Wang in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 12 (Décembre 2011) 

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Time Integration in Discontinuous Deformation Analysis / Doolin, David M. in Journal of engineering mechanics, Vol. 130 N°3 (Mars 2004)

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