Documents disponibles écrits par cet auteur

Effects of the source on wave propagation in pile integrity testing / Hua-You Chai in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 9 (Septembre 2010) . - pp. 1200-1208 Titre : Effects of the source on wave propagation in pile integrity testing Type de document : texte imprimé Auteurs : Hua-You Chai, Auteur ; Phoon, Kok-Kwang, Auteur ; Dian-Ji Zhang, Auteur Année de publication : 2010 Article en page(s) : pp. 1200-1208 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Longitudinal  mode  Rayleigh  waves  Dispersion  Low-strain  integrity  testing  of  piles  Pulse  echo  method Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : One-dimensional stress wave theory is widely used to analyze quantitatively the reflections in low-strain integrity testing of piles. However, a point or disk loading produces body and Rayleigh waves near the pile top. The multireflections of these waves from the lateral surface of a pile are present in the wave field near the pile top. Effects of three-dimensional waves on the near field responses are obvious. These effects can be interpreted erroneously by an inexperienced user as “noises” or “pile anomalies.” To investigate wave propagation in the longitudinal direction, the behavior of the waves in the far field (some distance below the pile top) is studied by theoretical analysis of the longitudinal modes in free cylinders and numerical simulations. The wave pattern at the pile top is analyzed based on the response of an elastic half-space to a harmonic disk loading. The results show that when the ratio of the characteristic length of an impact pulse to the cylinder radius is large enough, the components of Rayleigh waves in the wave field at the pile top are diminished; the waves in the far field behave approximately as plane waves; the responses at positions between 1/2R and 3/4R from the pile axis are less affected by the multireflections. The results from numerical simulations support the practical recommendation to use a ratio of characteristic wavelength to pile radius larger than four. Under this condition, the reflections from the far field (say deeper than two pile diameters) can be analyzed from the responses at receiver positions about 0.6R from the pile axis based on one-dimensional stress wave theory. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v136/i9/p1200_s1?isAuthorized=no [article] Effects of the source on wave propagation in pile integrity testing [texte imprimé] / Hua-You Chai, Auteur ; Phoon, Kok-Kwang, Auteur ; Dian-Ji Zhang, Auteur . - 2010 . - pp. 1200-1208. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 9 (Septembre 2010) . - pp. 1200-1208 Mots-clés : Longitudinal  mode  Rayleigh  waves  Dispersion  Low-strain  integrity  testing  of  piles  Pulse  echo  method Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : One-dimensional stress wave theory is widely used to analyze quantitatively the reflections in low-strain integrity testing of piles. However, a point or disk loading produces body and Rayleigh waves near the pile top. The multireflections of these waves from the lateral surface of a pile are present in the wave field near the pile top. Effects of three-dimensional waves on the near field responses are obvious. These effects can be interpreted erroneously by an inexperienced user as “noises” or “pile anomalies.” To investigate wave propagation in the longitudinal direction, the behavior of the waves in the far field (some distance below the pile top) is studied by theoretical analysis of the longitudinal modes in free cylinders and numerical simulations. The wave pattern at the pile top is analyzed based on the response of an elastic half-space to a harmonic disk loading. The results show that when the ratio of the characteristic length of an impact pulse to the cylinder radius is large enough, the components of Rayleigh waves in the wave field at the pile top are diminished; the waves in the far field behave approximately as plane waves; the responses at positions between 1/2R and 3/4R from the pile axis are less affected by the multireflections. The results from numerical simulations support the practical recommendation to use a ratio of characteristic wavelength to pile radius larger than four. Under this condition, the reflections from the far field (say deeper than two pile diameters) can be analyzed from the responses at receiver positions about 0.6R from the pile axis based on one-dimensional stress wave theory. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v136/i9/p1200_s1?isAuthorized=no

Efficient evaluation of reliability for slopes with circular slip surfaces using importance sampling / Jianye Ching in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 6 (Juin 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 6 (Juin 2009) . - pp. 768–777 Titre : Efficient evaluation of reliability for slopes with circular slip surfaces using importance sampling Type de document : texte imprimé Auteurs : Jianye Ching, Auteur ; Phoon, Kok-Kwang, Auteur ; Yu-Gang Hu, Auteur Année de publication : 2009 Article en page(s) : pp. 768–777 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Slope  stability  Monte  Carlo  method  System  reliability  Sampling Résumé : Evaluating the reliability of a slope is a challenging task because the possible slip surface is not known beforehand. Approximate methods via the first-order reliability method provide efficient ways of evaluating failure probability of the “most probable” failure surface. The tradeoff is that the failure probability estimates may be biased towards the unconservative side. The Monte Carlo simulation (MCS) is a viable unbiased way of estimating the failure probability of a slope, but MCS is inefficient for problems with small failure probabilities. This study proposes a novel way based on the importance sampling technique of estimating slope reliability that is unbiased and yet is much more efficient than MCS. In particular, the critical issue of the specification of the importance sampling probability density function will be addressed in detail. Three examples of slope reliability will be used to demonstrate the performance of the new method. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000035 [article] Efficient evaluation of reliability for slopes with circular slip surfaces using importance sampling [texte imprimé] / Jianye Ching, Auteur ; Phoon, Kok-Kwang, Auteur ; Yu-Gang Hu, Auteur . - 2009 . - pp. 768–777. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 6 (Juin 2009) . - pp. 768–777 Mots-clés : Slope  stability  Monte  Carlo  method  System  reliability  Sampling Résumé : Evaluating the reliability of a slope is a challenging task because the possible slip surface is not known beforehand. Approximate methods via the first-order reliability method provide efficient ways of evaluating failure probability of the “most probable” failure surface. The tradeoff is that the failure probability estimates may be biased towards the unconservative side. The Monte Carlo simulation (MCS) is a viable unbiased way of estimating the failure probability of a slope, but MCS is inefficient for problems with small failure probabilities. This study proposes a novel way based on the importance sampling technique of estimating slope reliability that is unbiased and yet is much more efficient than MCS. In particular, the critical issue of the specification of the importance sampling probability density function will be addressed in detail. Three examples of slope reliability will be used to demonstrate the performance of the new method. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000035

Observations on limit equilibrium–based slope reliability problems with inclined weak seams / Jianye Ching in Journal of engineering mechanics, Vol. 136 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 136 N° 10 (Octobre 2010) . - pp.1220-1233 Titre : Observations on limit equilibrium–based slope reliability problems with inclined weak seams Type de document : texte imprimé Auteurs : Jianye Ching, Auteur ; Phoon, Kok-Kwang, Auteur ; Yu-Gang Hu, Auteur Année de publication : 2010 Article en page(s) : pp.1220-1233 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Slope  stability  Monte  Carlo  method  Reliability  Sampling  Limit  equilibrium. Résumé : This study addresses the complexity of slope reliability problems based on limit equilibrium methods (LEMs). The main focus is on the existence of multiple failure modes that poses difficulty to many LEM-based slope reliability methods. In particular, when weak seams are present, the failure modes associated with those seams may be difficult to detect. A systematic way of searching the failure modes is proposed, and its robustness over slopes with or without weak seams is demonstrated. It is found that in the presence of weak seams, assuming circular slip surfaces may cause underestimation of slope failure probability. The conclusion of the study promotes the use of finite elements as the stability method for reliability evaluation because it is not necessary to search for failure surfaces in finite-element stability analysis. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v136/i10/p1220_s1?isAuthorized=no [article] Observations on limit equilibrium–based slope reliability problems with inclined weak seams [texte imprimé] / Jianye Ching, Auteur ; Phoon, Kok-Kwang, Auteur ; Yu-Gang Hu, Auteur . - 2010 . - pp.1220-1233. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 136 N° 10 (Octobre 2010) . - pp.1220-1233 Mots-clés : Slope  stability  Monte  Carlo  method  Reliability  Sampling  Limit  equilibrium. Résumé : This study addresses the complexity of slope reliability problems based on limit equilibrium methods (LEMs). The main focus is on the existence of multiple failure modes that poses difficulty to many LEM-based slope reliability methods. In particular, when weak seams are present, the failure modes associated with those seams may be difficult to detect. A systematic way of searching the failure modes is proposed, and its robustness over slopes with or without weak seams is demonstrated. It is found that in the presence of weak seams, assuming circular slip surfaces may cause underestimation of slope failure probability. The conclusion of the study promotes the use of finite elements as the stability method for reliability evaluation because it is not necessary to search for failure surfaces in finite-element stability analysis. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v136/i10/p1220_s1?isAuthorized=no

Pratical Inverse Approach for Forecasting Nonlinear Hydrological Time Series / Phoon, Kok-Kwang in Journal of hydrologic engineering, Vol. 7, N° 2 (Mars/Avril 2002) 

Public ISBD [article]  in Journal of hydrologic engineering > Vol. 7, N° 2 (Mars/Avril 2002) . - 116-128 p. Titre : Pratical Inverse Approach for Forecasting Nonlinear Hydrological Time Series Titre original : Approche Inverse de Pratique pour la Série Chronologique Hydrologique Non-Linéaire de Bâti Antérieur Type de document : texte imprimé Auteurs : Phoon, Kok-Kwang, Auteur ; Liong, Shie-Yue, Auteur ; Liaw, Chih-Young ; Islam, M. N., Auteur Article en page(s) : 116-128 p. Note générale : Hydrologie Langues : Anglais (eng) Mots-clés : Time  series  analysis  Correlation  Hydrologie  Forecasting  Analyse  de  série  chronologique  Corrélation  Hydrologie  Prévisions Index. décimale : 551.4 Résumé : This Paper presents a pratical inverse approach for forecasting nonlinear hydrological time series. The Proposed approach involves (1) calibrating the delay time, embedding dimension and number of nearest neighbors simultaneously using a single definite criterion, namely, optimum prediction accuracy; (2) verifying that the optimal parameters have wider applicability outside thescope of calibration; and (3) demonstrating that chaotic behavior is present when optimal parameters are used in conjunction with existing system characterization tools. The Proposed approach was shown to be better than the standard approach for a theoretical chaotic time series (Markey-Glass) and two real runoff time series (Tryggevaelde catchment in Denmark and Altamaha river at Doctortown, Ga.). Cet article présente une approche inverse pratical pour la série chronologique hydrologique non-linéaire de prévisions. L'approche proposée implique (1) calibrant le temps de retarder, incluant la dimension et le nombre des voisins les plus proches employant simultanément un critère défini simple, à savoir, exactitude optima de prévision ; (2) vérifiant que les paramètres optimaux ont une applicabilité plus large en dehors de thescope de calibrage ; et (3) démontrant que le comportement chaotique est présent où des paramètres optimaux sont employés en même temps que les outils existants de caractérisation de système. L'approche proposée s'est avérée meilleure que l'approche standard pour une série chronologique chaotique théorique (Markey-Verre) et deux vraies séries chronologiques d'écoulement (captation de Tryggevaelde dans le fleuve du Danemark et de l'Altamaha chez Doctortown, Ga.). En ligne : cvepkk@nus.edu.sq, [article] Pratical Inverse Approach for Forecasting Nonlinear Hydrological Time Series = Approche Inverse de Pratique pour la Série Chronologique Hydrologique Non-Linéaire de Bâti Antérieur [texte imprimé] / Phoon, Kok-Kwang, Auteur ; Liong, Shie-Yue, Auteur ; Liaw, Chih-Young ; Islam, M. N., Auteur . - 116-128 p. Hydrologie Langues : Anglais (eng) in Journal of hydrologic engineering > Vol. 7, N° 2 (Mars/Avril 2002) . - 116-128 p. Mots-clés : Time  series  analysis  Correlation  Hydrologie  Forecasting  Analyse  de  série  chronologique  Corrélation  Hydrologie  Prévisions Index. décimale : 551.4 Résumé : This Paper presents a pratical inverse approach for forecasting nonlinear hydrological time series. The Proposed approach involves (1) calibrating the delay time, embedding dimension and number of nearest neighbors simultaneously using a single definite criterion, namely, optimum prediction accuracy; (2) verifying that the optimal parameters have wider applicability outside thescope of calibration; and (3) demonstrating that chaotic behavior is present when optimal parameters are used in conjunction with existing system characterization tools. The Proposed approach was shown to be better than the standard approach for a theoretical chaotic time series (Markey-Glass) and two real runoff time series (Tryggevaelde catchment in Denmark and Altamaha river at Doctortown, Ga.). Cet article présente une approche inverse pratical pour la série chronologique hydrologique non-linéaire de prévisions. L'approche proposée implique (1) calibrant le temps de retarder, incluant la dimension et le nombre des voisins les plus proches employant simultanément un critère défini simple, à savoir, exactitude optima de prévision ; (2) vérifiant que les paramètres optimaux ont une applicabilité plus large en dehors de thescope de calibrage ; et (3) démontrant que le comportement chaotique est présent où des paramètres optimaux sont employés en même temps que les outils existants de caractérisation de système. L'approche proposée s'est avérée meilleure que l'approche standard pour une série chronologique chaotique théorique (Markey-Verre) et deux vraies séries chronologiques d'écoulement (captation de Tryggevaelde dans le fleuve du Danemark et de l'Altamaha chez Doctortown, Ga.). En ligne : cvepkk@nus.edu.sq,

Probabilistic analysis of soil-water characteristic curves / Phoon, Kok-Kwang in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 3 (Mars 2010) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 3 (Mars 2010) . - pp. 445-455 Titre : Probabilistic analysis of soil-water characteristic curves Type de document : texte imprimé Auteurs : Phoon, Kok-Kwang, Auteur ; Anastasia Santoso, Auteur ; Ser-Tong Quek, Auteur Article en page(s) : pp. 445-455 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Unsaturated  soils  Soil-water  characteristic  curve  Curve  fitting  Probability  Translation  Lognormal  Correlation  Random  vector Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Direct measurement of the soil-water characteristic curve (SWCC) is costly and time consuming. A first-order estimate from statistical generalization of experimental data belonging to soils with similar textural and structural properties is useful. A simple approach is to fit the data with a nonlinear function and to construct an appropriate probability model of the curve-fitting parameters. This approach is illustrated using sandy clay loam, loam, loamy sand, clay, and silty clay data in Unsaturated Soil Database. This paper demonstrates that a lognormal random vector is suitable to model the curve-fitting parameters of the SWCC. Other probability models using normal, gamma, Johnson, and other distributions do not provide better fit than the proposed lognormal model. The engineering impact of adopting a probabilistic SWCC is briefly discussed by studying the uncertainty of unsaturated shear strength due to the uncertainty of SWCC. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...] [article] Probabilistic analysis of soil-water characteristic curves [texte imprimé] / Phoon, Kok-Kwang, Auteur ; Anastasia Santoso, Auteur ; Ser-Tong Quek, Auteur . - pp. 445-455. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 3 (Mars 2010) . - pp. 445-455 Mots-clés : Unsaturated  soils  Soil-water  characteristic  curve  Curve  fitting  Probability  Translation  Lognormal  Correlation  Random  vector Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Direct measurement of the soil-water characteristic curve (SWCC) is costly and time consuming. A first-order estimate from statistical generalization of experimental data belonging to soils with similar textural and structural properties is useful. A simple approach is to fit the data with a nonlinear function and to construct an appropriate probability model of the curve-fitting parameters. This approach is illustrated using sandy clay loam, loam, loamy sand, clay, and silty clay data in Unsaturated Soil Database. This paper demonstrates that a lognormal random vector is suitable to model the curve-fitting parameters of the SWCC. Other probability models using normal, gamma, Johnson, and other distributions do not provide better fit than the proposed lognormal model. The engineering impact of adopting a probabilistic SWCC is briefly discussed by studying the uncertainty of unsaturated shear strength due to the uncertainty of SWCC. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...]

Singapore Rainfall Behavior: Chaotic? / Sivakumar, Bellie in Journal of hydrologic engineering, Vol. 4, N°1 (Janvier 1999)

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Validation of a new 2D failure mechanism for the stability analysis of a pressurized tunnel face in a spatially varying sand / Guilhem Mollon in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

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