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Αντικείμενο της παρούσας διατριβής αποτελεί η ανάλυση της συμπεριφοράς αξονικά φορτιζόμενου πασσάλου, η οποία μπορεί να οδηγήσει σε απώλεια φέρουσας ικανότητας. Συγκεκριμένα εξετάζεται η στατική δυσκαμψία του πασσάλου για τις περιπτώσεις ομοιογενούς και ανομοιογενούς εδάφους. Για την επίλυση του προβλήματος αναπτύχθηκε απλή αναλυτική ενεργειακή μέθοδος, η οποία βασίζεται στη θεωρία Winkler και στη χρήση συνάρτησης σχήματος, η οποία περιγράφει αξιόπιστα τις μετατοπίσεις κατά μήκος του πασσάλου. Το έδαφος γύρω από τον πάσσαλο προσομοιώνεται με κατακόρυφα γραμμικά ή μη ελατήρια τύπου Winkler, τα οποία εφαρμόζονται στην παρειά του πασσάλου αλλά και στη βάση του. Με επιλογή κατάλληλης συνάρτησης σχήματος και καμπυλών «τ-w» και «Pb-wb» και μετά από επαναληπτική διαδικασία εφαρμογής της μεθόδου, επιτυγχάνεται με ικανοποιητική ακρίβεια η τιμή της δυσκαμψίας για κατακόρυφη μετακίνηση στην κεφαλή του πασσάλου. / The present thesis deals with the analysis of the axial static response of a single pile, which may lead to bearing capacity loss. Specifically, the static stiffness of the pile located both in homogeneous and in inhomogeneous soil, is studied. For the analysis a simple energy method is employed, based on Winkler theory and on use of a shape function which represents reliably the deflected shape of the pile. The soil around the pile is simulated with vertical linear or nonlinear Winkler springs, applied to the sidewall of the pile and its base. Realistic predictions can be achieved for the value of stiffness of axially loaded piles, after iterative application of the method, by using the appropriate shape functions, “ τ-w “ and “Pb-wb” curves.

The properties of natural soil are inherently variable and influence design decisions in geotechnical engineering. Apart from the inherent variability of the soil, the variability may arise due to measurement of soil properties in the field or laboratory tests and model errors. These wide ranges of variability in soil are expressed in terms of mean, variance and autocorrelation function using probability/reliability based models. The most common term used in reliability based design is the reliability index, which is a probabilistic measure of assurance of performance of structure. The main objective of the reliability based design is to quantify probability of failure/reliability of a geotechnical system considering variability in the design parameters and associated safety. In foundation design, reliability based design is useful compared to deterministic factor of safety approach. Several design codes of practice recommend the use of limit state design concept based on probabilistic models, and suggest that, development of reliability based design methodologies for practical use are of immense value. The objective of the present study is to propose reliability based design methodologies for pile foundations under static and seismic loads. The work presented in this dissertation is subdivided into two parts, namely design of pile foundations under static vertical and lateral loading; and design of piles under seismic loading, embedded in non-liquefiable and liquefiable soil. The significance of consideration of variability in soil parameters in the design of pile foundation is highlighted. A brief review of literature is presented in Chapter 2 on current pile design methods under vertical, lateral and seismic loads. It also identifies the scope of the work. Chapter 3 discusses the methods of analysis which are subsequently used for the present study. Chapter 4 presents the reliability based design methodology for vertically and laterally loaded piles based on cone penetration test data for cohesive soil. CPT data from Konaseema area in India is used for analysis. Ultimate limit sate and serviceability limit state are considered for reliability based design using CPT data and load displacement curves. Chapter 5 presents the load resistance factor design (LRFD) of vertically and laterally loaded piles based on load test data. Reliability based code calibrated partial factors are determined considering bias in failure criteria, model bias and variability in load and resistance. Chapter 6 illustrates a comprehensive study on the effect of soil spatial variability on response of vertically and laterally loaded pile foundations in undrained clay. Two-dimensional finite difference program, FLAC2D (Itasca 2005) is used to model the soil and pile. The response of pile foundations due to the effect of variance and spatial correlation of undrained shear strength is studied using Monte Carlo simulation. The influence of spatial variability on the propagation and formation of failure near the pile foundation is also examined. Chapter 7 describes reliability based design methodology of piles in non-liquefiable soil. The seismic load on pile foundation is determined from code specified elastic design response spectrum using pseudo-static approach. Variability in seismic load and soil undrained shear strength are incorporated. The effects of soil relative densities, pile diameters, earthquake predominant frequencies and peak acceleration values on the two plausible failure mechanisms; bending and buckling are examined in Chapter 8. The two-dimensional finite difference analysis is used for dynamic analysis. A probabilistic approach is proposed to identify governing failure modes of piles in liquefiable soil in Chapter 9. The variability in the soil parameters namely SPT-N value, friction angle, shear modulus, bulk modulus, permeability and shear strain at 50% of modulus ratio is considered. Monte Carlo simulation is used to determine the probability of failure. A well documented case of the failed pile of Showa Bridge in 1964 Niigata earthquake is considered as case example. Based on the studies reported in this dissertation, it can be concluded that the reliability based design of pile foundations considering variability and spatial correlation of soil enables a rational choice of design loads. The variability in the seismic design load and soil shear strength can quantify the risk involved for pile design in a rational basis. The identification of depth of liquefiable soil layer is found to be most important to identify failure mechanisms of piles in liquefiable soil. Considerations of soil type, earthquake intensity, predominant frequency of earthquake, pile material, variability of soil are also significant.

Scour is a phenomenon of soil erosion around foundations under currents and waves. It is a major cause for the disruption to water-borne structures such as bridges and marine structures. Pile foundations supporting these structures are required to be designed against the scour damage. However, at present, there is no accepted method for the design of piles in scoured conditions probably due to an inadequate understanding of scour effects on foundations. Although numerous efforts have been made to evaluate the scour effects on single piles using numerical simulations and centrifuges tests, the scour susceptibility of piles in different soil properties is still not well understood. Furthermore, there is no study concerning scour effects on the lateral responses of pile groups. Therefore, a series of three-dimensional finite element (FE) parametric analyses were conducted to investigate scour effects on lateral behavior of both single piles and free-head pile groups by varying scour-hole dimensions, soil properties, pile properties, and pile group configurations. Moreover, to facilitate the routine design, a modified p-y method that was modified based on the widely used p-y method was proposed for both scoured single piles and pile groups, and was validated against the results from the FE analyses. The results show that scour induced lateral capacity loss to both single piles and pile groups, which was approximately 10% more in dense sands than that in loose sands. Simplification of local scour as a general scour that has been commonly used in general design practice resulted in a maximum of 17% underestimate of lateral capacity of pile foundations. Pile groups were more susceptible to scour than single piles under equivalent scour conditions. A pile group with smaller pile spacing or larger pile numbers tended to experience less lateral capacity loss due to scour. / Graduate / 2020-08-19

Apresenta-se uma metodologia de projeto de fundações por estacas incluindo probabilidade de ruína. Considera-se que a complexidade do comportamento geológico-geotécnico do maciço de solo e do elemento estrutural de fundação, submetidos às ações aleatórias ambientais e funcionais, pode ser avaliada por meio das variáveis aleatórias resistência e solicitação. Estatisticamente, a metodologia proposta supõe que a população da fundação é finita, e que os estimadores extraídos das sondagens de simples reconhecimento e das provas de carga podem ser representativos da população (Aoki, 2002), também podem ser avaliados pelas estatísticas de ordem. Aplica-se esta metodologia na fundação do Píer 3 do Porto de Vila do Conde localizado no Estado do Pará, tendo como compartimentação geológica a formação Barreiras. Conclui-se, de modo geral, que esta metodologia pode ser aplicada nas obras de fundações por estacas, especialmente, para auxiliar nas tomadas de decisões. / A methodology of pile foundation projects is presented incorporating ruin probability. It is considered that the complexity of the geological and geotechnical behaviors of the soil mass and the structural element of foundation, subjected to environmental and functional random actions, can be evaluated by strength and solicitation variables. Statistically, the proposed methodology assumes that the population of the foundation is finite, and that the extracted estimators of the standard penetration tests (SPT) and the load tests could be representative of the population (Aoki, 2002). The extracted estimators of the said tests can also be evaluated by the order statistics. This methodology is applied in the Pier 3 foundation of Porto de Vila do Conde, Pará State, which is underlain by the Barreiras formation. It is concluded that in most cases, this methodology could be applied to pile foundations, especially, in taking decisions.

Apresenta-se uma metodologia de projeto de fundações por estacas incluindo probabilidade de ruína. Considera-se que a complexidade do comportamento geológico-geotécnico do maciço de solo e do elemento estrutural de fundação, submetidos às ações aleatórias ambientais e funcionais, pode ser avaliada por meio das variáveis aleatórias resistência e solicitação. Estatisticamente, a metodologia proposta supõe que a população da fundação é finita, e que os estimadores extraídos das sondagens de simples reconhecimento e das provas de carga podem ser representativos da população (Aoki, 2002), também podem ser avaliados pelas estatísticas de ordem. Aplica-se esta metodologia na fundação do Píer 3 do Porto de Vila do Conde localizado no Estado do Pará, tendo como compartimentação geológica a formação Barreiras. Conclui-se, de modo geral, que esta metodologia pode ser aplicada nas obras de fundações por estacas, especialmente, para auxiliar nas tomadas de decisões. / A methodology of pile foundation projects is presented incorporating ruin probability. It is considered that the complexity of the geological and geotechnical behaviors of the soil mass and the structural element of foundation, subjected to environmental and functional random actions, can be evaluated by strength and solicitation variables. Statistically, the proposed methodology assumes that the population of the foundation is finite, and that the extracted estimators of the standard penetration tests (SPT) and the load tests could be representative of the population (Aoki, 2002). The extracted estimators of the said tests can also be evaluated by the order statistics. This methodology is applied in the Pier 3 foundation of Porto de Vila do Conde, Pará State, which is underlain by the Barreiras formation. It is concluded that in most cases, this methodology could be applied to pile foundations, especially, in taking decisions.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23484号 / 工博第4896号 / 新制||工||1765(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 渦岡 良介, 教授 木村 亮, 准教授 澤村 康生 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

"Brownfields" are real estate property with subsurface or surface contamination. The redevelopment of Brownfields is required to clean, improve and protect the environment. Piles foundations are often used in Brownfields to support structures. Regulators are concerned about the environmental safety of pile foundations in Brownfields sites. Piling in Brownfields may lead to transport of contaminants from the contaminated region to the underground aquifers. The purpose of this investigation is to determine the potential for contaminant transport due to pile foundation in Brownfields. This investigation is an extension of previous research conducted at the University of New Orleans and ascertains the potential for contaminant transport from concrete piles of different shape, depth of penetration and method of installation. The results of large scale model tests and Finite Element studies are presented. The investigation indicates the possibility of contamination only in selected cases of piles.

A macroelement is developed for soil-structure interaction analyses of piles in liquefiable soils, which captures efficiently the fundamental mechanisms of saturated granular soil behavior. The mechanical model comprises a nonlinear Winkler-type model that accounts for soil resistance acting along the circumference of the pile, and a coupled viscous damper that simulates changes in radiation damping with increasing material non-linearity. Three-dimensional (3D) finite element (FE) simulations are conducted for a pile in radially homogeneous soil to identify the critical parameters governing the response. The identified parameters, i.e., hydraulic conductivity, loading rate of dynamic loading, dilation angle and liquefaction potential are then expressed in dimensionless form. Next, the macroelement parameters are calibrated as a function of the soil properties and the effective stress. A semi-empirical approach that accounts for the effects of soil-structure interaction on pore pressure generation in the vicinity of pile is used to detect the onset of liquefaction. The predictions are compared with field data obtained using blast induced liquefaction and centrifuge tests and found to be in good agreement. Finally, the macroelement formulation is extended to account for coupling in both lateral directions. FEM simulations indicate that response assuming no coupling between the two horizontal directions for biaxial loading tends to overestimate the soil resistance and fails to capture features like 'apparent negative stiffness', 'strain hardening' and 'rounded corners'.