Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15340号 / 工博第3219号 / 新制||工||1485(附属図書館) / 27818 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 井合 進, 教授 岡 二三生, 教授 木村 亮 / 学位規則第4条第1項該当

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Geotechnical engineering is strongly associated with large uncertainties. Exploring a medium (soil) that is almost entirely and completely hidden from us is no easy task. Investigations can be made only at discrete points, and the majority of a specific soil volume is never tested. All soils experience inherent spatial variability, which contributes to some uncertainty in the design process of a geotechnical structure. Furthermore, uncertainties also arise during testing and when design properties are inferred from these tests. To master the art of making decisions in the presence of uncertainties, probabilistic description of soil properties and reliability-based design play vital roles. Historically, the observational method (sometimes referred to as the “learn-as-you-go-approach”), sprung from ideas by Karl Terzaghi and later formulated by Ralph Peck, has been used in projects where the uncertainties are large and difficult to assess. The design approach is still highly suitable for numerous situations and is defined in Eurocode 7 for geotechnical design. In paper I, the Eurocode definition of the observational method is discussed. This paper concluded that further work in the probabilistic description of soil properties is highly needed, and, by extension, reliability-based design should be used in conjunction with the observational method. Although great progress has been made in the field of reliability-based design during the past decade, few geotechnical engineers are familiar with probabilistic approaches to design. In papers II and III, aspects of probabilistic descriptions of soil properties and reliability-based design are discussed. The connection between performing qualitative investigations and potential design savings is discussed in paper III. In the paper, uncertainties are assessed for two sets of investigations, one consisting of more qualitative investigations and hence with less uncertainty. A simplified Bayesian updating technique, referred to as “the multivariate approach”, is used to cross-validate data to reduce the evaluated total uncertainty. Furthermore, reliability-based design was used to compare the two sets of investigations with the calculated penetration depth for a sheet-pile wall. The study is a great example of how a small amount of both time and money (in the pre-investigation phase) can potentially lead to greater savings in the final design. / <p>QC 20160201</p> / TRUST, Transparent Underground Structures

Le comportement mécanique des sols granulaires est un élément important à prendre en compte dans l'ingénierie géotechnique. Les approches de modélisation actuelles pour le comportement des sols granulaires utilisent des relations constitutives phénoménologiques basées sur la mécanique classique du continuum. Ce problème peut être contourné en utilisant des relations constitutives multi-échelles basées sur les principes thermodynamiques avec variables internes. En utilisant une approche multi-échelle, cette thèse tente de construire des relations constitutives multi-échelles qui tiennent compte de la microstructure des sols granulaires et les mettre en oeuvre pour résoudre des problèmes géotechniques à la fois en petites et grandes déformations. La thèse vise à: 1) construire une relation constitutive multiéchelle pour les sols granulaires secs à partir d'un cadre thermodynamique qui nécessite moins d'hypothèses ad hoc; 2) étendre les formulations thermomécaniques multi-échelles aux sols granulaires partiellement saturés pour lesquels un modèle micromécanique est formulé; 3) implémenter le modèle en utilisant un algorithme d'intégration implicite dans un code aux éléments finis; 4) appliquer le modèle pour analyser l'instabilité des sols granulaires dans les cas de ruptures localisées et diffuses; et 5) démontrer la capacité de l'approche multi-échelle à résoudre certains problèmes géotechniques typiques en mettant en oeuvre le modèle dans un code aux éléments finis explicite. L'approche multi-échelle proposée aboutit à un outil de simulation qui fournit des informations précieuses sur les problèmes d'ingénierie depuis l'échelle des grains jusqu’à l’échelle de la structure. / The mechanical behaviour of granular soils is an important aspect in geotechnical engineering. Current modelling approaches for the behaviour of granular soils employ phenomenological constitutive relations based upon classical continuum mechanics. This problem can be circumvented by using multiscale constitutive relations based on thermodynamic principles with internal variables. Using a multiscale approach, this thesis attempts to construct multiscale constitutive relations that account for the microstructure of granular soilsand to demonstrate their capabilities in solving geotechnical problems at both small and large deformations. The thesis aims to: 1) construct a multiscale constitutive relation for dry granular soils based on a thermodynamic framework which requires fewer ad hoc assumptions; 2) extend the multiscale thermomechanical formulations for partially saturated granularsoils for which a micromechanical model is formulated; 3)implement the model using an implicit integration algorithm in a finite element code; 4) apply the model to analyse the instability of granular soils for both localised and diffuse failures; and 5) demonstrate the capability of the multiscale approach in solving some typical geotechnical problems by implementing the model in an explicit finite element code. The proposed multiscale approach offers a simulation tool that provides valuable insights into engineering problems from the grain to the structure scale.

A major instrumented geosynthetic reinforced approach embankment was constructed to 5.5 m elevation above ground, with prefabricated vertical drains, over a soft compressible clay deposit at Leneghan, Newcastle, Australia in May 1995. The field monitoring of settlements for over six years shows that the embankment manifests significant creep. The instrumentation, field performance and the finite element analyses for predicting the long-term performance of this embankment are described in this thesis. The maximum settlement of 1.1 m was observed one year after the completion of construction. However, the embankment continued to settle at a rate of 0.4 mm/day for the next 5 years. The horizontal displacements of 0.09-0.14 m at various locations and the maximum reinforcement strains of 0.67% were recorded. A numerical model was developed to perform a fully coupled large deformation elasto-viscoplastic finite element analysis for this performance prediction based on creep model proposed by Kutter and Sathialingam (1992). The foundation soil was modelled with creep material behaviour using six noded linear strain triangular elements. A well-documented case history ??? Sackville embankment, New Brunswick, Canada was analysed using this model as a benchmark problem and the model was found to predict all the behaviour characteristics reasonably well. The results obtained from finite element analysis using this model are shown to be in reasonable agreement with the observed performance of Leneghans embankment in terms of settlements, horizontal displacements, excess pore pressures and geosynthetic strains. But, the prediction of settlements was less than satisfactory beyond April 1999. Finite element analyses were performed to study the sensitivity of this embankment behaviour on the variation of hydraulic conductivity values and geosynthetic reinforcement properties. This sensitivity study indicated that the kv variation, the kh/kv ratio and the nominal values of geosynthetic properties adopted in the benchmark analysis are reasonable enough for the long-term behaviour prediction.

A major instrumented geosynthetic reinforced approach embankment was constructed to 5.5 m elevation above ground, with prefabricated vertical drains, over a soft compressible clay deposit at Leneghan, Newcastle, Australia in May 1995. The field monitoring of settlements for over six years shows that the embankment manifests significant creep. The instrumentation, field performance and the finite element analyses for predicting the long-term performance of this embankment are described in this thesis. The maximum settlement of 1.1 m was observed one year after the completion of construction. However, the embankment continued to settle at a rate of 0.4 mm/day for the next 5 years. The horizontal displacements of 0.09-0.14 m at various locations and the maximum reinforcement strains of 0.67% were recorded. A numerical model was developed to perform a fully coupled large deformation elasto-viscoplastic finite element analysis for this performance prediction based on creep model proposed by Kutter and Sathialingam (1992). The foundation soil was modelled with creep material behaviour using six noded linear strain triangular elements. A well-documented case history ??? Sackville embankment, New Brunswick, Canada was analysed using this model as a benchmark problem and the model was found to predict all the behaviour characteristics reasonably well. The results obtained from finite element analysis using this model are shown to be in reasonable agreement with the observed performance of Leneghans embankment in terms of settlements, horizontal displacements, excess pore pressures and geosynthetic strains. But, the prediction of settlements was less than satisfactory beyond April 1999. Finite element analyses were performed to study the sensitivity of this embankment behaviour on the variation of hydraulic conductivity values and geosynthetic reinforcement properties. This sensitivity study indicated that the kv variation, the kh/kv ratio and the nominal values of geosynthetic properties adopted in the benchmark analysis are reasonable enough for the long-term behaviour prediction.