Documents disponibles écrits par cet auteur

Bayesian framework for characterizing geotechnical model uncertainty / J. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 7 (Juillet 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 7 (Juillet 2009) . - pp. 932–940 Titre : Bayesian framework for characterizing geotechnical model uncertainty Type de document : texte imprimé Auteurs : J. Zhang, Auteur ; Zhang, L. M., Auteur ; Wilson H. Tang, Auteur Année de publication : 2009 Article en page(s) : pp. 932–940 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Bayesian  analysis  Uncertainty  principles  Slope  stability  Centrifuge  model  Reliability Résumé : As any model is only an abstraction of the real world, model uncertainty always exists. The magnitude of model uncertainty is important for geotechnical decision making. If model uncertainty is not considered, the geotechnical predictions and hence the decisions based on the geotechnical predictions might be biased. In this study, a framework for characterizing geotechnical model uncertainty using observation data is proposed. The framework is based on the concept of multivariable Bayesian updating, in which the statistics of model uncertainty are updated using observed performance data. Uncertainties in both input parameters and observed data can be considered in the proposed framework. To bypass complex computational works involved in the proposed framework, a practical approximate solution is presented. The proposed framework is illustrated by characterizing the model uncertainty of four limit equilibrium methods for slope stability analysis using quality centrifuge test data. Parametric study in the illustrative example shows that both quality and quantity of the performance data could affect the determination of the model uncertainty, and that such effects can be systematically quantified with the proposed method. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000018 [article] Bayesian framework for characterizing geotechnical model uncertainty [texte imprimé] / J. Zhang, Auteur ; Zhang, L. M., Auteur ; Wilson H. Tang, Auteur . - 2009 . - pp. 932–940. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 7 (Juillet 2009) . - pp. 932–940 Mots-clés : Bayesian  analysis  Uncertainty  principles  Slope  stability  Centrifuge  model  Reliability Résumé : As any model is only an abstraction of the real world, model uncertainty always exists. The magnitude of model uncertainty is important for geotechnical decision making. If model uncertainty is not considered, the geotechnical predictions and hence the decisions based on the geotechnical predictions might be biased. In this study, a framework for characterizing geotechnical model uncertainty using observation data is proposed. The framework is based on the concept of multivariable Bayesian updating, in which the statistics of model uncertainty are updated using observed performance data. Uncertainties in both input parameters and observed data can be considered in the proposed framework. To bypass complex computational works involved in the proposed framework, a practical approximate solution is presented. The proposed framework is illustrated by characterizing the model uncertainty of four limit equilibrium methods for slope stability analysis using quality centrifuge test data. Parametric study in the illustrative example shows that both quality and quantity of the performance data could affect the determination of the model uncertainty, and that such effects can be systematically quantified with the proposed method. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000018

Bayesian model calibration using geotechnical centrifuge tests / L. L. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N°2 (Février 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N°2 (Février 2009) . - pp. 291–299 Titre : Bayesian model calibration using geotechnical centrifuge tests Type de document : texte imprimé Auteurs : L. L. Zhang, Auteur ; W. H. Tang, Auteur ; Zhang, L. M., Auteur Année de publication : 2009 Article en page(s) : pp. 291–299 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Centrifuge  model  Geotechnical  models  Slope  stability  Rainfall  Calibration  Bayesian  analysis  Reliability Résumé : The predicted performance using a geotechnical prediction model is expected to deviate from reality. A practical approach to assess the model error is through calibration with observed performances in physical model tests. In this paper, a Bayesian framework of model calibration using centrifuge modeling tests is proposed and the procedure of model calibration is illustrated. Two centrifuge tests conducted to investigate the performance of soil slopes under rainfall conditions are used to calibrate a coupled hydromechanical analysis model. It is found that for centrifuge tests with different levels of soil variability, the test with a smaller variability of soil properties is more efficient for model calibration. According to the concept of random field, a centrifuge model with a larger model size and accelerated to a lower acceleration is better for model calibration. When the discrepancy between the performance interpreted from the centrifuge model and the field performance is small, the improvement of the reliability estimation for a new slope is significant. However, when there is little information about the discrepancy, the reliability estimation cannot be significantly improved by the information from centrifuge modeling. The proposed procedure is shown to be able to quantify the calibration effects of centrifuge tests and may be used to achieve a more reliable calibration. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282009%29135%3A2%2829 [...] [article] Bayesian model calibration using geotechnical centrifuge tests [texte imprimé] / L. L. Zhang, Auteur ; W. H. Tang, Auteur ; Zhang, L. M., Auteur . - 2009 . - pp. 291–299. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N°2 (Février 2009) . - pp. 291–299 Mots-clés : Centrifuge  model  Geotechnical  models  Slope  stability  Rainfall  Calibration  Bayesian  analysis  Reliability Résumé : The predicted performance using a geotechnical prediction model is expected to deviate from reality. A practical approach to assess the model error is through calibration with observed performances in physical model tests. In this paper, a Bayesian framework of model calibration using centrifuge modeling tests is proposed and the procedure of model calibration is illustrated. Two centrifuge tests conducted to investigate the performance of soil slopes under rainfall conditions are used to calibrate a coupled hydromechanical analysis model. It is found that for centrifuge tests with different levels of soil variability, the test with a smaller variability of soil properties is more efficient for model calibration. According to the concept of random field, a centrifuge model with a larger model size and accelerated to a lower acceleration is better for model calibration. When the discrepancy between the performance interpreted from the centrifuge model and the field performance is small, the improvement of the reliability estimation for a new slope is significant. However, when there is little information about the discrepancy, the reliability estimation cannot be significantly improved by the information from centrifuge modeling. The proposed procedure is shown to be able to quantify the calibration effects of centrifuge tests and may be used to achieve a more reliable calibration. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282009%29135%3A2%2829 [...]

Behavior of coarse widely graded soils under low confining pressures / H. F. Zhao in Journal of geotechnical and geoenvironmental engineering, Vol. 139 N° 1 (Janvier 2013) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 139 N° 1 (Janvier 2013) . - pp. 35–48 Titre : Behavior of coarse widely graded soils under low confining pressures Type de document : texte imprimé Auteurs : H. F. Zhao, Auteur ; Zhang, L. M., Auteur ; D. S. Chang, Auteur Année de publication : 2013 Article en page(s) : pp. 35–48 Note générale : geotechnique Langues : Anglais (eng) Mots-clés : coarse-grained  soils;  compression;  landslides;  microstructure;  shear  strength;  soil  compaction;  soil  pressure Résumé : Colluvial soils are usually coarse and widely graded. Shallow-seated failures occur frequently in colluvial soil deposits during rainfall infiltration. This paper investigates the behavior of coarse, widely graded soils under very low confining pressures of 5–25 kPa encountered in shallow-seated failures. Isotropic consolidation tests, drained triaxial tests, and undrained triaxial tests were conducted on several widely graded soils with different coarse contents but with the same void ratio of 0.62. With increasing coarse content, the soil microstructure changes from a fines-controlled structure to a coarse-controlled structure after a critical coarse content of approximately 70%. Silty sand with gravel with a coarse content close to the critical value exhibits the highest compressibility because of the presence of large interaggregate pores. Even under very low confining pressures, such soil still shows strong contractive behavior during drained loading, and generates large positive pore-water pressures during undrained loading. This explains why shallow-seated failures occur frequently in colluvial soil deposits caused by rainfall infiltration. Soils with lower or higher coarse contents than the critical value may show dilative behavior under the same low confining pressures. The critical state friction angle increases with the coarse content. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000755 [article] Behavior of coarse widely graded soils under low confining pressures [texte imprimé] / H. F. Zhao, Auteur ; Zhang, L. M., Auteur ; D. S. Chang, Auteur . - 2013 . - pp. 35–48. geotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 139 N° 1 (Janvier 2013) . - pp. 35–48 Mots-clés : coarse-grained  soils;  compression;  landslides;  microstructure;  shear  strength;  soil  compaction;  soil  pressure Résumé : Colluvial soils are usually coarse and widely graded. Shallow-seated failures occur frequently in colluvial soil deposits during rainfall infiltration. This paper investigates the behavior of coarse, widely graded soils under very low confining pressures of 5–25 kPa encountered in shallow-seated failures. Isotropic consolidation tests, drained triaxial tests, and undrained triaxial tests were conducted on several widely graded soils with different coarse contents but with the same void ratio of 0.62. With increasing coarse content, the soil microstructure changes from a fines-controlled structure to a coarse-controlled structure after a critical coarse content of approximately 70%. Silty sand with gravel with a coarse content close to the critical value exhibits the highest compressibility because of the presence of large interaggregate pores. Even under very low confining pressures, such soil still shows strong contractive behavior during drained loading, and generates large positive pore-water pressures during undrained loading. This explains why shallow-seated failures occur frequently in colluvial soil deposits caused by rainfall infiltration. Soils with lower or higher coarse contents than the critical value may show dilative behavior under the same low confining pressures. The critical state friction angle increases with the coarse content. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000755

Breaching parameters for earth and rockfill dams / Xu, Y. in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 12 (Décembre 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 12 (Décembre 2009) . - pp. 1957–1970 Titre : Breaching parameters for earth and rockfill dams Type de document : texte imprimé Auteurs : Xu, Y., Auteur ; Zhang, L. M., Auteur Année de publication : 2010 Article en page(s) : pp. 1957–1970 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : DamsDam  failureDam  safetyErosionReservoirsRisk  management Résumé : Dam risk analysis is at the heart of dam failure prevention and mitigation. In order to assess dam risk, it is essential to conduct a quantitative analysis of the process of a dam breach, which can be described by such parameters as breach geometry, breaching duration, and peak outflow rate. The main objective of this paper is to develop robust empirical formulas with physical meaning for predicting dam breaching parameters based on past dam failure data. A database of 182 earth and rockfill dam failure cases has been compiled; among these cases nearly one-half are for large dams higher than 15 m. A multiparameter nonlinear regression model is recommended to develop empirical relationships between five breaching parameters (breach depth, breach top width, average breach width, peak outflow rate, and failure time) and five selected dam and reservoir control variables (dam height, reservoir shape coefficient, dam type, failure mode, and dam erodibility). The relative importance of each control variable is evaluated. The dam erodibility is found to be the most important factor, influencing all five breaching parameters. The reservoir shape coefficient and the failure mode also play an important role in the prediction models. Two case studies are presented to show the application of the empirical models developed in this paper. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000162 [article] Breaching parameters for earth and rockfill dams [texte imprimé] / Xu, Y., Auteur ; Zhang, L. M., Auteur . - 2010 . - pp. 1957–1970. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 12 (Décembre 2009) . - pp. 1957–1970 Mots-clés : DamsDam  failureDam  safetyErosionReservoirsRisk  management Résumé : Dam risk analysis is at the heart of dam failure prevention and mitigation. In order to assess dam risk, it is essential to conduct a quantitative analysis of the process of a dam breach, which can be described by such parameters as breach geometry, breaching duration, and peak outflow rate. The main objective of this paper is to develop robust empirical formulas with physical meaning for predicting dam breaching parameters based on past dam failure data. A database of 182 earth and rockfill dam failure cases has been compiled; among these cases nearly one-half are for large dams higher than 15 m. A multiparameter nonlinear regression model is recommended to develop empirical relationships between five breaching parameters (breach depth, breach top width, average breach width, peak outflow rate, and failure time) and five selected dam and reservoir control variables (dam height, reservoir shape coefficient, dam type, failure mode, and dam erodibility). The relative importance of each control variable is evaluated. The dam erodibility is found to be the most important factor, influencing all five breaching parameters. The reservoir shape coefficient and the failure mode also play an important role in the prediction models. Two case studies are presented to show the application of the empirical models developed in this paper. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000162

Characterization of dual-structure pore-size distribution of soil / X. Li in Canadian geotechnical journal, Vol. 46 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Canadian geotechnical journal > Vol. 46 N° 2 (Fevrier 2009) . - pp. 129–141 Titre : Characterization of dual-structure pore-size distribution of soil Type de document : texte imprimé Auteurs : X. Li, Auteur ; Zhang, L. M., Auteur Article en page(s) : pp. 129–141 Note générale : Sciences de la Terre Langues : Anglais (eng) Mots-clés : Compaction  Pore-size  distribution  Soil  fabric  Dual  porosity  Saturation  Drying  Compaction  Distribution  de  la  dimension  des  pores  Assemblage  du  sol  Porosité  double  Saturation  Séchage Index. décimale : 550 Sciences auxiliaires de la géologie. Résumé : The microporosity structure of soil provides important information in understanding the shear strength, compressibility, water-retention ability, and hydraulic conductivity of soils. It is a soil characteristic that depends on sample preparation method and wetting–drying history. A comprehensive study of the microporosity structure of a lean clay with sand was conducted in this research to investigate variations of the microporosity structure during compaction, saturation, and drying processes. Scanning electron microscopy was used to observe the microporosity structure of soil sample surfaces. Mercury intrusion porosimetry was used to measure the microporosity structure quantitatively by showing the relationship between cumulative pore volumes and pore radius. The experimental results show that a dual-porosity structure (i.e., interaggregate pores and intra-aggregate pores) forms during the compaction process. The interaggregate pores are compressible and the associated volume is closely related to the final void ratio of the compacted sample. Changes to interaggregate pores is dominant during compaction, but changes to intra-aggregate pores is dominant during saturation and drying. Based on the experimental results, a dual-porosity structure model was developed by relating the pore-size distribution to the void ratio. Consequently, the pore-size distribution at any void ratio can be predicted. La structure de la microporosité des sols révèle des informations importantes pour la compréhension de la résistance au cisaillement, de la compressibilité, de la capacité de rétention d’eau et de la conductivité hydraulique des sols. La microporosité est une caractéristique du sol qui dépend de la méthode de préparation de l’échantillon ainsi que de son historique de saturation – drainage. L’étude présentée consiste en une investigation de la variation de la structure de la microporosité d’une argile avec sable durant sa compaction, saturation et drainage. Le microscope électronique à balayage a été utilisé pour observer la microporosité à la surface des échantillons. La porosimétrie par intrusion au mercure a évalué la structure de la microporosité quantitativement en démontrant la relation entre le volume cumulatif des pores et le rayon des pores. Les résultats expérimentaux montrent qu’une structure de porosité double (pores inter-agrégats et pores intra-agrégats) est formée durant le processus de compaction. Les pores inter-agrégats sont compressibles et leur volume est étroitement associé à l’indice des vides final du sol compacté. Les modifications aux pores inter-agrégats sont prédominantes durant le processus de compaction, tandis que les modifications aux pores intra-agrégats surviennent principalement durant la saturation et le drainage. Basé sur les résultats expérimentaux, un modèle de structure de porosité double a été développé en reliant la distribution de la dimension des pores et l’indice des vides. De cette façon, la distribution de la dimension des pores peut être prédite pour n’importe quel indice des vides. DEWEY : 550 ISSN : 0008-3674 En ligne : http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=f [...] [article] Characterization of dual-structure pore-size distribution of soil [texte imprimé] / X. Li, Auteur ; Zhang, L. M., Auteur . - pp. 129–141. Sciences de la Terre Langues : Anglais (eng) in Canadian geotechnical journal > Vol. 46 N° 2 (Fevrier 2009) . - pp. 129–141 Mots-clés : Compaction  Pore-size  distribution  Soil  fabric  Dual  porosity  Saturation  Drying  Compaction  Distribution  de  la  dimension  des  pores  Assemblage  du  sol  Porosité  double  Saturation  Séchage Index. décimale : 550 Sciences auxiliaires de la géologie. Résumé : The microporosity structure of soil provides important information in understanding the shear strength, compressibility, water-retention ability, and hydraulic conductivity of soils. It is a soil characteristic that depends on sample preparation method and wetting–drying history. A comprehensive study of the microporosity structure of a lean clay with sand was conducted in this research to investigate variations of the microporosity structure during compaction, saturation, and drying processes. Scanning electron microscopy was used to observe the microporosity structure of soil sample surfaces. Mercury intrusion porosimetry was used to measure the microporosity structure quantitatively by showing the relationship between cumulative pore volumes and pore radius. The experimental results show that a dual-porosity structure (i.e., interaggregate pores and intra-aggregate pores) forms during the compaction process. The interaggregate pores are compressible and the associated volume is closely related to the final void ratio of the compacted sample. Changes to interaggregate pores is dominant during compaction, but changes to intra-aggregate pores is dominant during saturation and drying. Based on the experimental results, a dual-porosity structure model was developed by relating the pore-size distribution to the void ratio. Consequently, the pore-size distribution at any void ratio can be predicted. La structure de la microporosité des sols révèle des informations importantes pour la compréhension de la résistance au cisaillement, de la compressibilité, de la capacité de rétention d’eau et de la conductivité hydraulique des sols. La microporosité est une caractéristique du sol qui dépend de la méthode de préparation de l’échantillon ainsi que de son historique de saturation – drainage. L’étude présentée consiste en une investigation de la variation de la structure de la microporosité d’une argile avec sable durant sa compaction, saturation et drainage. Le microscope électronique à balayage a été utilisé pour observer la microporosité à la surface des échantillons. La porosimétrie par intrusion au mercure a évalué la structure de la microporosité quantitativement en démontrant la relation entre le volume cumulatif des pores et le rayon des pores. Les résultats expérimentaux montrent qu’une structure de porosité double (pores inter-agrégats et pores intra-agrégats) est formée durant le processus de compaction. Les pores inter-agrégats sont compressibles et leur volume est étroitement associé à l’indice des vides final du sol compacté. Les modifications aux pores inter-agrégats sont prédominantes durant le processus de compaction, tandis que les modifications aux pores intra-agrégats surviennent principalement durant la saturation et le drainage. Basé sur les résultats expérimentaux, un modèle de structure de porosité double a été développé en reliant la distribution de la dimension des pores et l’indice des vides. De cette façon, la distribution de la dimension des pores peut être prédite pour n’importe quel indice des vides. DEWEY : 550 ISSN : 0008-3674 En ligne : http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=f [...]

Consolidation of a Finite Transversely Isotropic Soil Layer on a Rough Impervious Base / S. L. Chen in Journal of engineering mechanics, Vol. 131, N°12 (Decembre 2005) 

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Efficient probabilistic back-analysis of slope stability model parameters / J. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 1 (Janvier 2010) 

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Microporosity structure of coarse granular soils / Zhang, L. M. in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 10 (Octobre 2010) 

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Optimization of pile groups using hybrid genetic algorithms / Chan, C. M. in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 4 (Avril 2009) 

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Permeability tensor and representative elementary volume of saturated cracked soil / J. H. Li in Canadian geotechnical journal, Vol. 46 N° 8 (Août 2009) 

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Reliability-based optimization of geotechnical systems / J. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 12 (Décembre 2011) 

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Slope reliability analysis considering site-specific performance information / J. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 3 (Mars 2011) 

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Spatial variability of in situ weathered soil / S. M. Dasaka in Géotechnique, Vol. 62 N° 5 (Mai 2012) 

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Uncertainties in geologic profiles versus variability in pile founding depth / Zhang, L. M. in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 11 (Novembre 2010) 

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Uncertainties of field pullout resistance of soil nails / L. L. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 7 (Juillet 2009) 

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