<p>The focus of this study is on potential problems resulting from construction on expansive soils in Kibaha region, Tanzania. For the fact that most of the affected structures are founded on expansive soils, a clear understanding of the soil behaviour and their interaction with structures, specifically as they relate to shallow foundations, has been of more interest to the study in order to evaluate properly the source of the problem.</p><p>The geotechnical behaviour of expansive clay soils is investigated by looking into the geomorphologic, geological and climatic conditions and mineralogical composition of the soils in the study area. The geotechnical results are linked with the performance of the foundation as well as structures.</p><p>Two sites, representative of known problem-areas in Kibaha were selected for geotechnical tests. Geotechnical site investigation consisted of open trial pits, profile description and the collection of both disturbed and undisturbed samples.</p><p>The collected samples were submitted to soil laboratories at KTH and DIT for mineralogical composition tests, natural water content, density, Atterberg limits and swell tests (free swell and swelling pressure). The results of this investigation indicate that soil in Kibaha contains clay (31%), have high liquid limit (59%) and plastic limit (37%) which indicate high potential swell.</p><p>Since swell potential and swell pressure are key properties of expansive soils, the swell parameters were measured by free swell tests and one-dimensional oedometer swell tests respectively. The free swell ranged from 100% to 150% and the swell pressure was in the region of 45 kPa.</p><p>The properties of expansive soils were confirmed by the x-ray diffraction test which showed the presence of montmorillonite in the soil. It is from this fact that the source of the problem is in the expansive soils coupled with poor building materials.</p><p>Physical conditions of the surveyed properties in the area confirmed the hypothesis of building damages due to poor building materials triggered by expansive soils. In support of the obtained data, the actual behaviour of the foundations is supplemented with prototypes of strip foundations whose performances are to be monitored over a long period. Finally, suggested are the ways forward to solve the problem of foundation on expansive soil.</p>

The focus of this study is on potential problems resulting from construction on expansive soils in Kibaha region, Tanzania. For the fact that most of the affected structures are founded on expansive soils, a clear understanding of the soil behaviour and their interaction with structures, specifically as they relate to shallow foundations, has been of more interest to the study in order to evaluate properly the source of the problem. The geotechnical behaviour of expansive clay soils is investigated by looking into the geomorphologic, geological and climatic conditions and mineralogical composition of the soils in the study area. The geotechnical results are linked with the performance of the foundation as well as structures. Two sites, representative of known problem-areas in Kibaha were selected for geotechnical tests. Geotechnical site investigation consisted of open trial pits, profile description and the collection of both disturbed and undisturbed samples. The collected samples were submitted to soil laboratories at KTH and DIT for mineralogical composition tests, natural water content, density, Atterberg limits and swell tests (free swell and swelling pressure). The results of this investigation indicate that soil in Kibaha contains clay (31%), have high liquid limit (59%) and plastic limit (37%) which indicate high potential swell. Since swell potential and swell pressure are key properties of expansive soils, the swell parameters were measured by free swell tests and one-dimensional oedometer swell tests respectively. The free swell ranged from 100% to 150% and the swell pressure was in the region of 45 kPa. The properties of expansive soils were confirmed by the x-ray diffraction test which showed the presence of montmorillonite in the soil. It is from this fact that the source of the problem is in the expansive soils coupled with poor building materials. Physical conditions of the surveyed properties in the area confirmed the hypothesis of building damages due to poor building materials triggered by expansive soils. In support of the obtained data, the actual behaviour of the foundations is supplemented with prototypes of strip foundations whose performances are to be monitored over a long period. Finally, suggested are the ways forward to solve the problem of foundation on expansive soil. / QC 20101118

Orientadores: Aloisio Ernesto Assan, Persio Leister de Almeida Barros / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-11T01:26:45Z (GMT). No. of bitstreams: 1 BobadillaGuadalupe_Ulises_D.pdf: 1151597 bytes, checksum: 005fbfba6e1ebd787b740be4f94cbf34 (MD5) Previous issue date: 2008 / Resumo: As características que determinam o comportamento de uma estrutura sob carregamento dinâmico são as massas dos vários elementos, a rigidez dos seus membros e a dissipação de energia. Para avaliar corretamente a resposta dinâmica de uma estrutura levando em conta os efeitos da interação, é necessário incorporar as propriedades dinâmicas do solo dentro da formulação matemática do modelo físico adotado. Referido à superestrutura, os efeitos da interação alteram a resposta estrutural final, devido à inter-relação dinâmica entre o movimento do solo e o movimento da base de fundação. Conseqüentemente, se primeiro se avalia o movimento da base de fundação [produto da interação solo-estrutura (SSI)], a resposta estrutural final poderá ser resolvida depois via análise modal da superestrutura. Esta conceituação é utilizada no presente trabalho. Aqui, todo o processo de análise é feito no domínio da freqüência. A resposta estrutural é avaliada através da chamada Transformada Implícita de Fourier (ImFT), implementando-se para isto um algoritmo computacional que avalia a resposta dinâmica utilizando a ImFT eficientemente. A ImFT é uma avaliação racional das matrizes envolvendo as transformadas discretas de Fourier (DFT), para num mesmo processo matricial achar a resposta dinâmica estrutural diretamente no domínio do tempo. Correntemente, para a análise no domínio da freqüência tem-se utilizado a FFT (Fast Fourier Transform); embora a FFT seja computacionalmente eficiente, apresenta-se aqui a ImFT, um outro processo computacional alternativo à FFT e bastante eficiente para certos tipos de carregamento tais como uma excitação sísmica, que é o carregamento utilizado nesta pesquisa / Abstract: The characteristics that determine the behavior of a structure under dynamic loading are the masses of various elements, the rigidity of its members and the dissipation of energy. To properly evaluate the dynamic response of a structure taking into account the effects of the interaction, it is necessary to incorporate the dynamic properties of the soil within the mathematical formulation of the physical model adopted. Referred to the superstructure, the effects of interaction modify the final structural response due to the dynamic interrelationship between the soil motion and the base of foundation motions. Consequently, if that first assesses the base of foundation motions [product of the soil-structure interaction effects (SSI)], the final structural response can be assessed later by modal analysis of the superstructure. This concept is used in this work. Here, the whole process of analysis is done in frequency domain. The structural response is evaluated by the so-called Implicit Fourier Transform (ImFT), implementing to this a computational algorithm that assesses the structural dynamic response using the ImFT efficiently. The ImFT is a rational assessment of matrices involving the Discrete Fourier Transform (DFT) for a same matrix process find structural dynamics response directly on time domain. Commonly, for the analysis in the frequency domain has been used the FFT (Fast Fourier Transform), although the FFT is efficiently, presents itself here the ImFT, another alternative computational algorithm and quite competent to certain types of loading such as a seismic excitation which is the loading used in this study / Doutorado / Estruturas / Doutor em Engenharia Civil

Thesis deals with problems of the soil-structure interaction. In the theoretical part is described the approach to mathematical modeling of structure-foundation-soil interaction. The subsoil models are further described in detail, including the models with piles (both static and dynamics models). In the next chapter there is described the dynamics theory of the systems with single or more degrees of freedom. There is also an analysis of propagation, reflection and refraction of mechanical one-dimensional waves (P-wave, S-wave) and spatial waves (P- wave, SV-wave, SH-wave) and waves in homogeneous half-space (R-wave L-wave). The numerical analysis is logically sorted from hand calculation of the parameter change influence on the modal characteristics to complex computational FEM model of the machine with a foundation on piles placed in the spatial block of soil. Numerical studies aim to determine the influence of the subsoil model on the modal characteristics and thus confirm the absolute necessity of the subsoil model in tasks of dynamics. The next goal is to determine the appropriate key parameters of the computational model: the size of finite element, suitable shape of subsoil model, suitable inclination of boundary condition and suitable boundary conditions. For creating of set of computational models was used language APDL in conjunction with ANSYS software interface. All used input files are listed in the Annex.