Documents disponibles écrits par cet auteur

Dynamic centrifuge testing of slickensided shear surfaces / Christopher L. Meehan in Journal of geotechnical and geoenvironmental engineering, Vol. 134 n°8 (Août 2008) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 134 n°8 (Août 2008) . - pp. 1086–1096 Titre : Dynamic centrifuge testing of slickensided shear surfaces Type de document : texte imprimé Auteurs : Christopher L. Meehan, Auteur ; Ross W. Boulanger, Auteur ; J. Michael Duncan, Auteur Année de publication : 2008 Article en page(s) : pp. 1086–1096 Note générale : Geotechnical and geotechnical engineering Langues : Anglais (eng) Mots-clés : Dynamic  stability  Clays  Residual  strength  Slope  stability  Earthquakes  Soil  deformation  Shear  strength  Overconsolidated  soils  Centrifuge Résumé : Movement along preexisting slickensided rupture surfaces in overconsolidated clay and clay shale slopes can represent a critical sliding mechanism during earthquakes. The seismic behavior of preexisting slickensided surfaces in overconsolidated clay was examined by performing dynamic centrifuge model tests of two slickensided sliding block models constructed using Rancho Solano lean clay. Dynamic shear displacements were concentrated along the preformed slickensided surfaces. The peak shear resistances mobilized along the slickensided surfaces during dynamic loading were 90–120% higher than the drained residual strength measured prior to shaking. To accurately predict the displacements of the sliding blocks using Newmark’s method, it was necessary to use dynamic strengths that were 37–64% larger than the drained residual strength of the soil. Dynamic loading caused a positive pore pressure response in the soil surrounding the slickensided planes. The postshaking shear strengths were 17–31% higher than those measured prior to shaking. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A8%2810 [...] [article] Dynamic centrifuge testing of slickensided shear surfaces [texte imprimé] / Christopher L. Meehan, Auteur ; Ross W. Boulanger, Auteur ; J. Michael Duncan, Auteur . - 2008 . - pp. 1086–1096. Geotechnical and geotechnical engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 134 n°8 (Août 2008) . - pp. 1086–1096 Mots-clés : Dynamic  stability  Clays  Residual  strength  Slope  stability  Earthquakes  Soil  deformation  Shear  strength  Overconsolidated  soils  Centrifuge Résumé : Movement along preexisting slickensided rupture surfaces in overconsolidated clay and clay shale slopes can represent a critical sliding mechanism during earthquakes. The seismic behavior of preexisting slickensided surfaces in overconsolidated clay was examined by performing dynamic centrifuge model tests of two slickensided sliding block models constructed using Rancho Solano lean clay. Dynamic shear displacements were concentrated along the preformed slickensided surfaces. The peak shear resistances mobilized along the slickensided surfaces during dynamic loading were 90–120% higher than the drained residual strength measured prior to shaking. To accurately predict the displacements of the sliding blocks using Newmark’s method, it was necessary to use dynamic strengths that were 37–64% larger than the drained residual strength of the soil. Dynamic loading caused a positive pore pressure response in the soil surrounding the slickensided planes. The postshaking shear strengths were 17–31% higher than those measured prior to shaking. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A8%2810 [...]

Exhumed geogrid-reinforced retaining wall / Leshchinsky, Dov 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. 1311-1323 Titre : Exhumed geogrid-reinforced retaining wall Type de document : texte imprimé Auteurs : Leshchinsky, Dov, Auteur ; Baris Imamoglu, Auteur ; Christopher L. Meehan, Auteur Article en page(s) : pp. 1311-1323 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Creep  Geogrids  Retaining  walls  Strain  gages  Stress  Reinforcement  Reinforced  wall Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : An instrumented geogrid-reinforced wall constructed on a highly compressible foundation was deconstructed 16 months after its completion, providing a unique opportunity to exhume and examine the instrumented geogrids that were used to construct the wall. The objectives of this post mortem study were: (1) to inspect the condition of the strain gauges that were attached to the geogrid layers before construction and to verify the reliability of their output; (2) to develop a procedure in which the residual (plastic) strains along exhumed geogrid panels could be determined; and (3) to assess the in situ strain and force distribution along geogrid panels based on the measured residual strains from the exhumed geogrids. After exhumation, it was observed that many of the attached strain gauges failed due to full or partial debonding from the geogrid, thus rendering outputs which potentially underestimated the actual strain. Combining aperture measurements of virgin and exhumed geogrids, all from the same manufacturing lots, enabled the assessment of residual strains following stress relaxation. Laboratory simulation of loading and unloading, including creep and relaxation, yielded a relationship between the measured residual strains and the in situ strain and force distribution; i.e., the residual strain fingerprint provided insight into the behavior of the geogrids within the wall prior to its deconstruction. The mobilized maximum tensile strains in the geogrid panels along the height of the wall were roughly uniform, in the range 4±1%. These findings imply that if the same type of reinforcement had been used throughout the height of the wall, the mobilized force along the height would have been relatively uniform. The back-calculated maximum force in the geogrids indicated that the factor of safety on the long-term strengths of the geogrids ranged from about 1.4 on the stronger/stiffer geogrid to about 1.8 on the weaker/softer geogrid. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...] [article] Exhumed geogrid-reinforced retaining wall [texte imprimé] / Leshchinsky, Dov, Auteur ; Baris Imamoglu, Auteur ; Christopher L. Meehan, Auteur . - pp. 1311-1323. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 10 (Octobre 2010) . - pp. 1311-1323 Mots-clés : Creep  Geogrids  Retaining  walls  Strain  gages  Stress  Reinforcement  Reinforced  wall Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : An instrumented geogrid-reinforced wall constructed on a highly compressible foundation was deconstructed 16 months after its completion, providing a unique opportunity to exhume and examine the instrumented geogrids that were used to construct the wall. The objectives of this post mortem study were: (1) to inspect the condition of the strain gauges that were attached to the geogrid layers before construction and to verify the reliability of their output; (2) to develop a procedure in which the residual (plastic) strains along exhumed geogrid panels could be determined; and (3) to assess the in situ strain and force distribution along geogrid panels based on the measured residual strains from the exhumed geogrids. After exhumation, it was observed that many of the attached strain gauges failed due to full or partial debonding from the geogrid, thus rendering outputs which potentially underestimated the actual strain. Combining aperture measurements of virgin and exhumed geogrids, all from the same manufacturing lots, enabled the assessment of residual strains following stress relaxation. Laboratory simulation of loading and unloading, including creep and relaxation, yielded a relationship between the measured residual strains and the in situ strain and force distribution; i.e., the residual strain fingerprint provided insight into the behavior of the geogrids within the wall prior to its deconstruction. The mobilized maximum tensile strains in the geogrid panels along the height of the wall were roughly uniform, in the range 4±1%. These findings imply that if the same type of reinforcement had been used throughout the height of the wall, the mobilized force along the height would have been relatively uniform. The back-calculated maximum force in the geogrids indicated that the factor of safety on the long-term strengths of the geogrids ranged from about 1.4 on the stronger/stiffer geogrid to about 1.8 on the weaker/softer geogrid. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...]

Relationship between the seismic coefficient and the unfactored geosynthetic force in reinforced earth structures / Farshid Vahedifard in Journal of geotechnical and geoenvironmental engineering, Vol. 138 N° 10 (Octobre 2012) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 138 N° 10 (Octobre 2012) . - pp.1209–1221. Titre : Relationship between the seismic coefficient and the unfactored geosynthetic force in reinforced earth structures Type de document : texte imprimé Auteurs : Farshid Vahedifard, Auteur ; Leshchinsky, Dov, Auteur ; Christopher L. Meehan, Auteur Année de publication : 2013 Article en page(s) : pp.1209–1221. Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Soil  stabilization  Geosynthetics  Seismic  design  Limit  equilibrium  Earthquakes Résumé : This paper presents an integrated analytical method for calculating the resultant unfactored geosynthetic force in reinforced earth structures under seismic loading conditions. The method utilizes a pseudostatic limit equilibrium approach for assessing the internal stability of a reinforced earth structure, assuming a potential rotational failure along a log spiral trace. A closed-form solution is presented for determining the sum of all horizontal forces mobilized in the geosynthetic reinforcement along their intersection with the critical log spiral surface. This mobilized sum is then redistributed among the individual layers to determine the unfactored reinforcement forces that are needed to resist the applied seismic acceleration. Parametric studies were utilized, and the results are presented in a series of design charts for different conditions. Such charts can be used to determine the required tensile strength of the reinforcement for a given seismic coefficient. Alternatively, for a given reinforcement strength, the formulation can also be used to determine the yield acceleration that is required for calculating seismic displacements. An advantage of the proposed methodology is that it determines the yield acceleration caused by rotation of the reinforced mass (internal stability), which allows for a rational, yet simple, assessment of the displacement related to the internal movement of the reinforced mass. The design charts illustrate the effect of earth structure backslope and the vertical seismic coefficient. The results also show the impact of the assumed location of the resultant reinforcement force under seismic loading conditions. Variations in the location of this force over a reasonable range have little impact on the results. The inclination of the backslope has a significant effect for earth structures with smaller batters and/or larger horizontal seismic coefficients. Additionally, vertical seismic coefficients with a downward direction increase the mobilized force in the geosynthetic reinforcement. ISSN : 1090-0241 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000701 [article] Relationship between the seismic coefficient and the unfactored geosynthetic force in reinforced earth structures [texte imprimé] / Farshid Vahedifard, Auteur ; Leshchinsky, Dov, Auteur ; Christopher L. Meehan, Auteur . - 2013 . - pp.1209–1221. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 138 N° 10 (Octobre 2012) . - pp.1209–1221. Mots-clés : Soil  stabilization  Geosynthetics  Seismic  design  Limit  equilibrium  Earthquakes Résumé : This paper presents an integrated analytical method for calculating the resultant unfactored geosynthetic force in reinforced earth structures under seismic loading conditions. The method utilizes a pseudostatic limit equilibrium approach for assessing the internal stability of a reinforced earth structure, assuming a potential rotational failure along a log spiral trace. A closed-form solution is presented for determining the sum of all horizontal forces mobilized in the geosynthetic reinforcement along their intersection with the critical log spiral surface. This mobilized sum is then redistributed among the individual layers to determine the unfactored reinforcement forces that are needed to resist the applied seismic acceleration. Parametric studies were utilized, and the results are presented in a series of design charts for different conditions. Such charts can be used to determine the required tensile strength of the reinforcement for a given seismic coefficient. Alternatively, for a given reinforcement strength, the formulation can also be used to determine the yield acceleration that is required for calculating seismic displacements. An advantage of the proposed methodology is that it determines the yield acceleration caused by rotation of the reinforced mass (internal stability), which allows for a rational, yet simple, assessment of the displacement related to the internal movement of the reinforced mass. The design charts illustrate the effect of earth structure backslope and the vertical seismic coefficient. The results also show the impact of the assumed location of the resultant reinforcement force under seismic loading conditions. Variations in the location of this force over a reasonable range have little impact on the results. The inclination of the backslope has a significant effect for earth structures with smaller batters and/or larger horizontal seismic coefficients. Additionally, vertical seismic coefficients with a downward direction increase the mobilized force in the geosynthetic reinforcement. ISSN : 1090-0241 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000701

Required unfactored strength of geosynthetic in reinforced earth structures / Leshchinsky, Dov in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 2 (Fevrier 2010) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 2 (Fevrier 2010) . - pp. 281-289 Titre : Required unfactored strength of geosynthetic in reinforced earth structures Type de document : texte imprimé Auteurs : Leshchinsky, Dov, Auteur ; Fan Zhu, Auteur ; Christopher L. Meehan, Auteur Article en page(s) : pp. 281-289 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Reinforced  soil  Slope  stability  Geosynthetics  Limit  equilibrium Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Current reinforced earth structure designs arbitrarily distinguish between reinforced walls and slopes, that is, the batter of walls is 20° or less while in slopes it is larger than 20°. This has led to disjointed design methodologies where walls employ a lateral earth pressure approach and slopes utilize limit equilibrium analyses. The earth pressure approach used is either simplified (e.g., ignoring facing effects), approximated (e.g., considering facing effects only partially), or purely empirical. It results in selection of a geosynthetic with a long-term strength that is potentially overly conservative or, by virtue of ignoring statics, potentially unconservative. The limit equilibrium approach used in slopes deals explicitly with global equilibrium only; it is ambiguous about the load in individual layers. Presented is a simple limit equilibrium methodology to determine the unfactored global geosynthetic strength required to ensure sufficient internal stability in reinforced earth structures. This approach allows for seamless integration of the design methodologies for reinforced earth walls and slopes. The methodology that is developed accounts for the sliding resistance of the facing. The results are displayed in the form of dimensionless stability charts. Given the slope angle, the design frictional strength of the soil, and the toe resistance, the required global unfactored strength of the reinforcement can be determined using these charts. The global strength is then distributed among individual layers using three different assumed distribution functions. It is observed that, generally, the assumed distribution functions have secondary effects on the trace of the critical slip surface. The impact of the distribution function on the required global strength of reinforcement is minor and exists only when there is no toe resistance, when the slope tends to be vertical, or when the soil has low strength. Conversely, the impact of the distribution function on the maximum unfactored load in individual layers, a value which is typically used to select the geosynthetics, can result in doubling its required long-term strength. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...] [article] Required unfactored strength of geosynthetic in reinforced earth structures [texte imprimé] / Leshchinsky, Dov, Auteur ; Fan Zhu, Auteur ; Christopher L. Meehan, Auteur . - pp. 281-289. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 2 (Fevrier 2010) . - pp. 281-289 Mots-clés : Reinforced  soil  Slope  stability  Geosynthetics  Limit  equilibrium Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Current reinforced earth structure designs arbitrarily distinguish between reinforced walls and slopes, that is, the batter of walls is 20° or less while in slopes it is larger than 20°. This has led to disjointed design methodologies where walls employ a lateral earth pressure approach and slopes utilize limit equilibrium analyses. The earth pressure approach used is either simplified (e.g., ignoring facing effects), approximated (e.g., considering facing effects only partially), or purely empirical. It results in selection of a geosynthetic with a long-term strength that is potentially overly conservative or, by virtue of ignoring statics, potentially unconservative. The limit equilibrium approach used in slopes deals explicitly with global equilibrium only; it is ambiguous about the load in individual layers. Presented is a simple limit equilibrium methodology to determine the unfactored global geosynthetic strength required to ensure sufficient internal stability in reinforced earth structures. This approach allows for seamless integration of the design methodologies for reinforced earth walls and slopes. The methodology that is developed accounts for the sliding resistance of the facing. The results are displayed in the form of dimensionless stability charts. Given the slope angle, the design frictional strength of the soil, and the toe resistance, the required global unfactored strength of the reinforcement can be determined using these charts. The global strength is then distributed among individual layers using three different assumed distribution functions. It is observed that, generally, the assumed distribution functions have secondary effects on the trace of the critical slip surface. The impact of the distribution function on the required global strength of reinforcement is minor and exists only when there is no toe resistance, when the slope tends to be vertical, or when the soil has low strength. Conversely, the impact of the distribution function on the maximum unfactored load in individual layers, a value which is typically used to select the geosynthetics, can result in doubling its required long-term strength. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...]