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Orientador: Kléber Pereira Lanças / Resumo: A eficiência tratória dos tratores equipados com pneus infláveis varia desde próximo de 90%, quando operando em concreto, até menos de 50% para trabalhos em solos soltos ou arenosos. As características trativas de um pneu dependem do tipo e condições do solo, tipo e geometria do pneu, formato das suas garras, carga no eixo e pressão de inflação do pneu. Este trabalho teve como objetivo quantificar e avaliar o contato pneu/solo com ênfase nos métodos para a obtenção da área de contato. A abordagem, visando uma solução analítica para o caso, seria de difícil execução e imprecisa, não fosse o uso da técnica de Elementos Finitos que tem demonstrado versatilidade, flexibilidade e excelentes resultados em casos semelhantes. A área de contato do pneu com o solo é a responsável, em grande parte, pelo desempenho do trator, afetando também características como, a patinagem de pneus e a tração. A abordagem do problema, em primeira instância, considerou um delineamento experimental com parcelas sub-divididas constituído de 48 tratamentos, assim distribuídos: a) Três tipos de pneu: Diagonal, Radial e BPAF (baixa pressão de inflação e alta flutuação). b) Dois níveis de pressões de inflação do pneu: Alta: 165,50 kPa (17 psi, pneus montados no eixo traseiro do trator), "Baixa/correta" para pneus montados no eixo traseiro do trator: 68,95 kPa (7 psi) ou para cada tipo de pneu respectivamente. c) Quatro magnitudes de carga vertical aplicada no pneu: 0,5 kN, 1,0 kN, 1,5 kN e 2,0 kN. d) Dois tipos de solo: amostra de solo agrícola arenoso ( s= 1,4g/cm3) e amostra de solo agrícola argiloso ( s= 1,2g/cm3). Para realização do experimento com os dois tipos e condições de solo, foi utilizado um equipamento para o ensaio estático de pneus individuais, denominado tanque de solo com dispositivo hidráulico de aplicação de carga... (Resumo completo, clicar acesso eletrônico abaixo). / Abstract: The tractive efficiency of tractors equipped with inflated tires varies from nearly 90%, whem working on concrete, to less than 50% when working on loose soil or sand. The tractive characteristics of a tire depend on soil conditions, tire geometry and lugs, axle load and tire pressure. This wok aimed to estimate the contact tire/soil with emphasis on methods of determination of contact area. The approach using an analytical solution for this case wold of hard execution and inaccurate, but the use of the finite element solutions has been shown versatile, flexible and with exelents results in similar cases. The contact area of tire with the soil is the major responsible by the performance, affected also characteristics like sliding and traction. The problem was considered like an experimental design with 48 treatments being: a) Tree kinds of the tires, bias, radial and B.P.A.F. (low inflation pression and high flutuation). b) Two levels of inflation pressure of the tire, high: 165,50 kPa for each kind of tire, respectively. c) Two types of soil: sample of agricultural sandy soil ( s= 1,4g/cm3) and sample of agricultural clay soil ( s= 1,2g/cm3). To realize the experiment with two soil types and conditions were used an equipment for static test of individual tires named soil bin with hydraulic device to apply the loads. For each test the tire/soil contact area was determinate using a method of digital picture area integration. The data were used to elaborate mathematical models that expressed the relation ships among loads and strains using the Finite Element Method. The tests proved that relationship to determine the contact areas for bias tires gained the worst results once the B.P.A.F. tires showed the bests one. The Radial tires showed always intermediates results compared with the other two types. The pressure cells installed into the soil bin always showed... (Complete abstract click electronic access below). / Doutor

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Made available in DSpace on 2014-06-11T19:31:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-02Bitstream added on 2014-06-13T19:41:56Z : No. of bitstreams: 1 santos_pib_dr_botfca.pdf: 1550423 bytes, checksum: bb57085eaf0754ffaf290736b53b5ece (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A eficiência tratória dos tratores equipados com pneus infláveis varia desde próximo de 90%, quando operando em concreto, até menos de 50% para trabalhos em solos soltos ou arenosos. As características trativas de um pneu dependem do tipo e condições do solo, tipo e geometria do pneu, formato das suas garras, carga no eixo e pressão de inflação do pneu. Este trabalho teve como objetivo quantificar e avaliar o contato pneu/solo com ênfase nos métodos para a obtenção da área de contato. A abordagem, visando uma solução analítica para o caso, seria de difícil execução e imprecisa, não fosse o uso da técnica de Elementos Finitos que tem demonstrado versatilidade, flexibilidade e excelentes resultados em casos semelhantes. A área de contato do pneu com o solo é a responsável, em grande parte, pelo desempenho do trator, afetando também características como, a patinagem de pneus e a tração. A abordagem do problema, em primeira instância, considerou um delineamento experimental com parcelas sub-divididas constituído de 48 tratamentos, assim distribuídos: a) Três tipos de pneu: Diagonal, Radial e BPAF (baixa pressão de inflação e alta flutuação). b) Dois níveis de pressões de inflação do pneu: Alta: 165,50 kPa (17 psi, pneus montados no eixo traseiro do trator), Baixa/correta para pneus montados no eixo traseiro do trator: 68,95 kPa (7 psi) ou para cada tipo de pneu respectivamente. c) Quatro magnitudes de carga vertical aplicada no pneu: 0,5 kN, 1,0 kN, 1,5 kN e 2,0 kN. d) Dois tipos de solo: amostra de solo agrícola arenoso ( s= 1,4g/cm3) e amostra de solo agrícola argiloso ( s= 1,2g/cm3). Para realização do experimento com os dois tipos e condições de solo, foi utilizado um equipamento para o ensaio estático de pneus individuais, denominado tanque de solo com dispositivo hidráulico de aplicação de carga... . / The tractive efficiency of tractors equipped with inflated tires varies from nearly 90%, whem working on concrete, to less than 50% when working on loose soil or sand. The tractive characteristics of a tire depend on soil conditions, tire geometry and lugs, axle load and tire pressure. This wok aimed to estimate the contact tire/soil with emphasis on methods of determination of contact area. The approach using an analytical solution for this case wold of hard execution and inaccurate, but the use of the finite element solutions has been shown versatile, flexible and with exelents results in similar cases. The contact area of tire with the soil is the major responsible by the performance, affected also characteristics like sliding and traction. The problem was considered like an experimental design with 48 treatments being: a) Tree kinds of the tires, bias, radial and B.P.A.F. (low inflation pression and high flutuation). b) Two levels of inflation pressure of the tire, high: 165,50 kPa for each kind of tire, respectively. c) Two types of soil: sample of agricultural sandy soil ( s= 1,4g/cm3) and sample of agricultural clay soil ( s= 1,2g/cm3). To realize the experiment with two soil types and conditions were used an equipment for static test of individual tires named soil bin with hydraulic device to apply the loads. For each test the tire/soil contact area was determinate using a method of digital picture area integration. The data were used to elaborate mathematical models that expressed the relation ships among loads and strains using the Finite Element Method. The tests proved that relationship to determine the contact areas for bias tires gained the worst results once the B.P.A.F. tires showed the bests one. The Radial tires showed always intermediates results compared with the other two types. The pressure cells installed into the soil bin always showed... (Complete abstract click electronic access below).

Some normally consolidated soft soils manifest strength sensitivity, ie these soil manifest strain softening when shear in an undrained mode. These soils, referred to as sensitive soft soils, have the typical features of strain hardening in drained shearing and strain softening in undrained shearing. The consolidation lines of these soils are also curved (concave upwards) in the semi-log space. However, under high consolidation stress or upon large shearing, these soils re-gain the features of re-constituted soil. Ground improvement methods like stone columns were reported as not effective when installed in the sensitive soft clays. But mechanism of the un-effectiveness of the stone columns remains unknown because of lack of a suitable and simple model for simulating the stress-strain behaviours of sensitive soft soils. Although these soils have a meta-stable micro-structure, models that developed for simulating structured firm soils are not suitable for simulating sensitive soft soil features. Thus, a new model was formulated. The new model can degenerate back to a Modified Cam Clay model. The ability of new model in simulating a range of behaviour was verified by using the finite difference (FD) method in solving the partial differential equations of the soil model for a range of tri-axial test conditions. The model was further implemented in coupled analysis formulation and coded into FEM program AFENA. Various cases with different soil parameters were then simulated and compared with the FD solutions for various triaxial tests so as to check the stability of the FEM code. The coupled FEA was then used to simulate the performance of geosynthetic-encased stone columns. A new stone column element and a geo-encasement element were developed and coded into AFENA. The stone column simulations were then done for both non-sensitive soils (represented by Modified Cam Clay model) and sensitive soft soil (represented by the new model). Parametric study was conducted to examine the performance of the geo-encased stone columns in both types of soils. Furthermore, two different installation methods: wished-in installation and full displacement installation were studied numerically. Cross comparison was done to investigate how the sensitive soft soil features interact with the installation method in affecting the performance of the geo-encased stone columns. A range of factors that influence the geosynthetic-encased stone columns performance installed in soft soils were also made clear.

Scour is a process of removing soils around foundations by currents and waves. For the pile-supported marine structures such as the monopile-supported offshore wind turbines (OWTs) and the pile-supported bridges, scour can decrease the pile capacities and alter the dynamic responses of the structures. At present, there is not a widely accepted method to estimate pile axial or lateral capacity under scoured conditions. For example, different recommendations are used among the existing design standards for estimation of the vertical effective stress and the resulting capacities for single piles under different scour conditions. None of the existing standards or design practice has even considered the scour effects on the behavior of pile groups. Furthermore, the investigation into the responses of piles under multiple hazards of scour and earthquakes is rarely reported. To address the foregoing limitations, this study first introduces an analytical solution to determining the vertical effective stress of soils around single isolated piles under scoured conditions and uses it to examine the limitations of the existing standards in estimation of pile tensile capacity (Chapter 1). The effect of soil-pile interface friction is highlighted. Next, the study proposes new approaches to investigating the combined effects of scour and earthquakes on the lateral responses of the monopile-supported OWTs in sand (Chapter 2) and soft clay (Chapter 3). Lastly, simple and practical methods are developed based on the p-y curve framework for analyzing the lateral responses of pile groups in sand (Chapter 4) and soft clay (Chapter 5) subjected to static lateral loading. The proposed methods in this study were encoded into a series of open-source computer scripts for engineering practice. They were verified with the 3D continuum finite element (FE) analyses. Using the proposed methods, standard methods, and 3D FE method, parametric analyses were conducted to investigate the scour effects on the lateral behavior of the monopile-supported OWTs under crustal earthquakes and that of the pile groups under static loading. The factors considered in the parametric study included effects of scour-hole dimensions, soil stress history, soil density, soil-pile interface behavior, soil liquefaction potential, pile group configurations, etc. Through the parametric analyses, the standard methods were critically assessed by comparing the results to those calculated by the proposed methods and 3D FE methods, and some design-related issues were also discussed. / Graduate

Master of Engineering (Research) / Soil surrounding a submarine buried pipeline consolidates as ocean waves propagate over the seabed surface. Conventional models for the analysis of soil behaviour near the pipeline assume a two-dimensional interaction problem between waves, the seabed soil, and the structure. In other words, it is often considered that water waves travel normal to the orientation of pipeline. However, the real ocean environment is three-dimensional and waves approach the structure from various directions. It is therefore the key objective of the present research to study the seabed behaviour in the vicinity of marine pipelines from a three-dimensional point of view. A three-dimensional numerical model is developed based on the Finite Element Method to analyse the so-called momentary behaviour of soil under the wave loading. In this model, the pipeline is assumed to be rigid and anchored within a rigid impervious trench. A non-slip condition is considered to exist between the pipe and the surrounding soil. Quasi-static soil consolidation equations are then solved with the aid of the proposed FE model. In this analysis, the seabed behaviour is assumed to be linear elastic with the soil strains remaining small. The influence of wave obliquity on seabed responses, i.e. the pore pressure and soil stresses, are then studied. It is revealed that three-dimensional characteristics systematically affect the distribution of soil response around the circumference of the underwater pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. Further, a parametric study is carried out to investigate the influence of soil, wave and pipeline properties on wave-associated pore pressure as well as principal effective and shear stresses within the porous bed, with the aid of proposed three-dimensional model. There is strong evidence in the literature that the failure of marine pipelines often stems from the instability of seabed soil close to this structure, rather than from construction deficiencies. The wave-induced seabed instability is either associated with the soil shear failure or the seabed liquefaction. Therefore, the developed three-dimensional FE model is used in this thesis to further investigate the instability of seabed soil in the presence of a pipeline. The widely-accepted criterion, which links the soil liquefaction to the wave-induced excess pressure is used herein to justify the seabed liquefaction. It should be pointed out that although the present analysis is only concerned with the momentary liquefaction of seabed soil, this study forms the basis for the three-dimensional analysis of liquefaction due to the residual mechanisms. The latter can be an important subject for future investigations. At the same time, a new concept is developed in this thesis to apply the dynamic component of soil stress angle to address the phenomenon of wave-associated soil shear failure. At this point, the influence of three-dimensionality on the potentials for seabed liquefaction and shear failure around the pipeline is investigated. Numerical simulations reveal that the wave obliquity may not notably affect the risk of liquefaction near the underwater pipeline. But, it significantly influences the potential for soil shear failure. Finally, the thesis proceeds to a parametric study on effects of wave, soil and pipeline characteristics on excess pore pressure and stress angle in the vicinity of the structure.

Master of Engineering (Research) / Soil surrounding a submarine buried pipeline consolidates as ocean waves propagate over the seabed surface. Conventional models for the analysis of soil behaviour near the pipeline assume a two-dimensional interaction problem between waves, the seabed soil, and the structure. In other words, it is often considered that water waves travel normal to the orientation of pipeline. However, the real ocean environment is three-dimensional and waves approach the structure from various directions. It is therefore the key objective of the present research to study the seabed behaviour in the vicinity of marine pipelines from a three-dimensional point of view. A three-dimensional numerical model is developed based on the Finite Element Method to analyse the so-called momentary behaviour of soil under the wave loading. In this model, the pipeline is assumed to be rigid and anchored within a rigid impervious trench. A non-slip condition is considered to exist between the pipe and the surrounding soil. Quasi-static soil consolidation equations are then solved with the aid of the proposed FE model. In this analysis, the seabed behaviour is assumed to be linear elastic with the soil strains remaining small. The influence of wave obliquity on seabed responses, i.e. the pore pressure and soil stresses, are then studied. It is revealed that three-dimensional characteristics systematically affect the distribution of soil response around the circumference of the underwater pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. Further, a parametric study is carried out to investigate the influence of soil, wave and pipeline properties on wave-associated pore pressure as well as principal effective and shear stresses within the porous bed, with the aid of proposed three-dimensional model. There is strong evidence in the literature that the failure of marine pipelines often stems from the instability of seabed soil close to this structure, rather than from construction deficiencies. The wave-induced seabed instability is either associated with the soil shear failure or the seabed liquefaction. Therefore, the developed three-dimensional FE model is used in this thesis to further investigate the instability of seabed soil in the presence of a pipeline. The widely-accepted criterion, which links the soil liquefaction to the wave-induced excess pressure is used herein to justify the seabed liquefaction. It should be pointed out that although the present analysis is only concerned with the momentary liquefaction of seabed soil, this study forms the basis for the three-dimensional analysis of liquefaction due to the residual mechanisms. The latter can be an important subject for future investigations. At the same time, a new concept is developed in this thesis to apply the dynamic component of soil stress angle to address the phenomenon of wave-associated soil shear failure. At this point, the influence of three-dimensionality on the potentials for seabed liquefaction and shear failure around the pipeline is investigated. Numerical simulations reveal that the wave obliquity may not notably affect the risk of liquefaction near the underwater pipeline. But, it significantly influences the potential for soil shear failure. Finally, the thesis proceeds to a parametric study on effects of wave, soil and pipeline characteristics on excess pore pressure and stress angle in the vicinity of the structure.