The investigation described in this thesis is aimed at determining the effect of heated air flow on the behaviour of capillary barriers. In order to achieve the objectives of this investigation, a number of tasks were undertaken, as described hereinafter. First, a laboratory scale testing was carried out to determine the effect of heated air flow on the volumetric water content (VWC) and matric suction in a layer of soil representing the coarse grained soil layer of a capillary barrier. Several types of instruments were used to measure the VWC, matric suction, and temperature at different locations within the soil. Next, a numerical analysis was undertaken to simulate the behaviour of the soil mass subjected to thermal changes in the laboratory experiments. Lastly, two case studies were analyzed with and without the heated air flow in the coarse grained soil layer to validate the proposed model. The method used in this investigation was based on: (1) application of temperature change at the perimeters of the pipes installed in the coarse grained soil layer near the interface between the fine grained and coarse grained soil layers; and, (2) application of suction as a boundary condition at the perforated parts of the pipes to decrease VWC and increase matric suction in the soil mass. Using this specific method, the results of the finite element analyses of the laboratory experiments and the two case studies demonstrated that the heated air flow through the coarse grained soil layer of a capillary barrier would improve its performance as a soil cover for a number of engineering applications. Comparisons of measured and calculated values of VWC and matric suction showed good agreement providing further proof of the validity of the method.

The main objective of this research is to use IGA as an efficient and robust alternative for numerical simulation of unsaturated seepage problems. Moreover, this research develops an IGA-based probabilistic framework that can properly account for the variability of soil hydraulic properties in the simulations. In the first part, IGA is used in a deterministic framework to solve a head-based form of Richards’ equation. It is shown that IGA is able to properly simulate changes in pore pressure at the soils interface. In the second part of this research, a new probabilistic framework, named random IGA (RIGA), is developed. A joint lognormal distribution function is used with IGA to perform Monte Carlo simulations. The results depict the statistical outputs relating to seepage quantities and pore water pressure. It is shown that pore water pressure, flow rate, etc. change considerably with respect to standard deviation and correlation of the model parameters.

Water moves in soil in response to potential gradients. The basic equation for this movement is the generalized flow equation: v = - KV0 in which v is volume of water passing through a unit area in unit time, K is the conductivity coefficient, V is the gradient operator (vector), and V 0 is the potential gradient.

Levees are earth structures used for flood protection. Due to their easy availability and low permeability, clays are the most common material used for the construction of levees. Clays are susceptible to desiccation cracks when subjected to long dry spells during summers. There has been an increased interest in studying the occurrence of cracks in soil mass. In particular, many experimental investigations for soils have been undertaken to learn about the crack pattern in earth embankment. However, there is a dearth of work that focuses on the numerical modeling of desiccation cracks effects on levees. This study has been undertaken to analyze the effect of desiccation cracking on the hydraulic behavior of an earth embankment under flooding conditions. A numerical model was developed using the finite element package CODE_BRIGHT. The model was validated from the data obtained from a small scale embankment experiment under controlled environmental conditions. As the phenomenon of desiccation cracking is highly random, a simple random model was developed to capture the variability in crack geometry. The random crack geometry was then passed on to the finite element mesh, so that a probabilistic analysis can be carried out using a Monte Carlo approach, for assessing the embankment’s integrity. The results obtained from the analysis such as time to steady state saturation and steady state flow rate at the outward slope were very interesting to study and provided an insight on the effect of desiccation cracks on unsaturated earth embankments.

Ce travail a pour objectif d’étudier la fissuration des sols due au séchage par des approches numérique et analytique. L’initiation et la propagation des fissures sont investiguées en utilisant un code de calcul aux éléments finis avec la présence des joints cohésifs. Les couplages entre le problème hydraulique et le comportement mécanique en présence des discontinuités sont considérés. La loi de la fissure cohésive est appliquée pour modéliser l’initiation et la propagation des fissures.Tout d’abord, les résultats d’un essai de séchage au laboratoire réalisé sur un sol argileux à l’état liquide sont utilisés afin d’évaluer la méthode numérique proposée. Les résultats numériques montrent que le modèle est capable de reproduire les tendances principales du processus de séchage. Elle souligne aussi l’importance des conditions aux limites dans l’initiation des fissures. Ensuite, une approche énergétique est proposée pour étudier l’initiation d’une fissure. Les énergies élastiques avant et après l’initiation de la fissure sont estimées par les deux approches analytique et numérique. L’énergie dissipée lors de l’initiation de la fissure est comparée avec le taux d’énergie pour créer une fissure. Les analyses montrent que le critère d’énergie peut est atteint avant le critère de contrainte. La dissipation de l’énergie cumulée correspond à la propagation instable lors de l’initiation de la fissure. De plus, le développement et la géométrie des fissures sont étudiés essentiellement par les simulations numériques avec plusieurs joints cohésifs. Les résultats numériques montrent que la fissuration se produit souvent progressivement pour former différentes familles de fissures par un processus dichotomique (une fissure apparait au milieu de deux fissures existantes). La propagation d’une fissure est brutale dans la phase d’initiation pour atteindre une profondeur appelée ‘ultime’. Les fissures dans chaque famille peuvent apparaitre simultanément à un même niveau de succion et présentent une même profondeur ultime. En se basant sur les résultats numériques et quelques analyses analytiques supplémentaires, des relations empiriques sont proposées afin de prédire l’espacement et la profondeur ultime des fissures. Finalement, quelques calculs préliminaires sont réalisés afin d’évaluer le potentiel de la méthode numérique proposée pour prédire la fissuration liée au séchage des ouvrages en terre / This work focuses on the analysis of desiccation cracking by numerical and analytical approaches. The initiation and the propagation of cracks are investigated by using a finite element code including cohesive joints elements. Coupling between the hydraulic and the mechanical processes in the presence of discontinuities is considered. The cohesive crack’s law is applied to simulate the initiation and the propagation of cracks.Results of a laboratory experiments performed on slurry clay soil are first used to evaluate the proposed numerical modelling method. The results show that the method is able to reproduce the main trends of desiccation process. The importance of boundary conditions are also discussed. Second, an energy approach is proposed to study the initiation of cracks. The energies before and after crack initiation are estimated by both numerical and analytical solutions. The energy released by cracking is then compared to the crack energy to discuss crack initiation conditions. The analysis shows that the energy criterion is reached before the stress criterion, and this can explain unstable crack propagation at the beginning. Third, the development and the geometry of desiccation cracks are studied by numerical simulation with several cohesive joints. The numerical results show that cracking occurs sequentially to form different cracks families with a dichotomy process (the subsequent cracks appear at the middle of two existing neighboring ones). The cracks in each family appear simultaneously and reach an identical ultimate depth. From the numerical results and additional analytical analysis, empirical correlations are proposed to predict the spacing and crack depth. Finally, some preliminary studies are performed showing that the proposed numerical method can be used to predict the desiccation crack phenomena observed on geotechnical earth structures

Compacted soils are frequently used as subgrade for pavements as well as commercial and residential buildings. The stiffness and shear strength properties of compacted soils, which are collectively denoted as Ω in this thesis, fluctuate with moisture content changes that result from the influence of environmental factors such as the evaporation and infiltration. For example, mechanistic pavement design methods require the information of resilient modulus (MR), which is the soil stiffness behavior under cyclic traffic loading, and its variation with respect to the soil moisture content determined from laboratory tests or estimation methods. Significant advances have been made during the last five decades to understand and model the variation of the Ω with respect to soil moisture content and soil suction (s) based on the principles of mechanics of unsaturated soils. There are a variety of models presently available in the literature relating the Ω to the s using different approaches. There are however uncertainties extending these models for predicting Ω - s relationships when they are used for a larger soil suction range. In addition, the good performance of these models are only valid for certain soil types for which they were developed and calibrated. Studies presented in this thesis are directed towards developing a unified methodology for modelling the relationship between the Ω and the s using limited while easy-to-obtain information. However, more emphasis has been focused on the MR - s relationships of pavement subgrade soils considering the need for the application of the mechanistic pavement design methods in Canada. The following studies have been conducted: (i) State-of-the-art review on existing equations in the literature for the MR - s relationships is summarized. A comparison study is followed to discuss the strengths and limitations of these equations; (ii) A unified methodology for modelling the Ω - s relationships is proposed. Experimental data on 25 different soils are used to verify the proposed unified methodology. The investigations are applied on small strain shear modulus, elastic modulus, and peak and critical shear strength. Good predictions are achieved for all of the investigated soils; (iii) Performance of the proposed methodology is examined for the MR - s relationships using experimental data of 11 subgrade soils. Reasonably good predictions are achieved for all of the subgrade soils; (iv) Extensive experimental investigations are conducted on the MR - s relationships for several subgrade soils collected from various regions in Canada. Experimental results suggest non-linear variation in the MR with respect to s, moisture content and the external stress. The measured results are modelled using the proposed methodology with adequate success; (v) Additional experimental investigations are performed to determine the variation of the elastic modulus (E) and unconfined compression strength (qu) with the s and the gravimetric moisture content (w) for several Canadian subgrade soils. An approach, which is developed extending the proposed unified methodology, is used to normalize the measured MR - w, E - w and qu - w relationships. It is shown that the normalized MR - w, E - w and qu - w relationships exhibit remarkable similarity and can be well described using the proposed approach. Such similarity in the normalized Ω - moisture content relationships are also corroborated using the experimental data on several other soils reported in the literature. The proposed unified methodology alleviates the need for the determination of the Ω - s relationships which requires elaborate testing equipment that needs the supervision of trained personnel and is also time-consuming and expensive. In addition, experimental programs in this thesis provide detailed experimental data on the MR, E, qu, and soil-water characteristic curves of Canadian subgrade soils. These data will be helpful for the better understanding of the hydro-mechanical behavior of the Canadian subgrade soils and for the implementation of the mechanistic pavement design method in Canada. The simple tools presented in this thesis are promising and encouraging for implementing the mechanics of unsaturated soils into conventional geotechnical engineering practice.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23476号 / 工博第4888号 / 新制||工||1764(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 三村 衛, 教授 肥後 陽介 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Deslizamentos em solos tropicais são frequentemente resultados do avanço de uma frente de umedecimento devido às águas das chuvas. O avanço desta frente de umedecimento provoca elevação da poro-pressão de água ou redução da sucção, e consequentemente, perda de resistência do solo. Este trabalho apresenta um estudo sobre a resistência ao cisalhamento dos solos não saturados, abrangendo uma fase experimental envolvendo ensaios de caracterização, resistência e obtenção das propriedades hidráulicas dos solos e um estudo numérico, com o objetivo de verificar o comportamento da poro-pressão no interior de um talude e a influência na sua estabilidade. Os ensaios de resistência foram realizados no aparato de cisalhamento direto, para a condição inundada, e no aparato de compressão simples com medida direta de sucção, por meio do tensiômetro de alta capacidade (TAC), para a condição não saturada. O equipamento TRIFLEX 2 foi utilizado para se determinar os coeficientes de permeabilidade na condição saturada, e as curvas de retenção foram obtidas utilizando-se a placa de sucção, o TAC e o método do papel filtro. A partir dos resultados obtidos na fase experimental, avaliou-se a influência das características das precipitações (duração e intensidade), condições inicias de sucção no talude e das propriedades hidráulicas dos solos na variação da poro-pressão de água, no interior do talude, ao longo do tempo. Paralelamente à variação da poro-pressão de água, foi obtida a variação do fator de segurança durante e após a precipitação. / Landslides in tropical soils are often the result of advance of the wetting due to rainfall. This advance results from an increase in pore water pressure, reduction in present soil matric suction, reduction in the shear strength of the soil. This work will present a study related to the shear strength of unsaturated soils, including an experimental study, involving characterization, shear strength tests and obtaining hydraulic characteristics of the soils. There is also a numeric study with the aim to analyze the pore water pressure behavior in slopes and its influence in the slope stability. The shear strength tests were carried out in the direct shear test device, for the flooded condition, and concerning the unconfined compression with direct measured matric suction using a high capacity tensiometer (HCT) placed at the base of the sample, for the unsaturated condition. The permeability tests were carried out with TRIFLEX 2 device, and the retention curves were determined using suction plate, HCT and filtered paper. The experimental data permitted the evaluation of the influence of the characteristics of the rainfall (duration and intensity), initial conditions of the slope and of the hydraulic characteristics of the soils in the pore-pressure change of water in the slope, during the test time. In parallel to the pore pressure change of water, the variations of the safety factors during and after the rainfall were obtained.

Taludes formados por solos na condição não saturada são muito comuns no Brasil. Nestes casos a poro-pressão de água contribui para a estabilidade desses taludes. Este trabalho pretende avaliar o efeito do tipo de revestimento superficial na alteração do perfil de poro-pressão de água provocado por fluxos gerados a partir de precipitações, evaporação e evapo-transpiração, e conseqüentemente na estabilidade de talude experimental. São apresentadas aqui as características geológico-geotécnica, geomorfológica, climática e pluviométrica de campo experimental implantado na zona leste de São Paulo/SP, onde foram instalados e monitorados tensiômetros, pluviômetro e medidor de nível dágua por um período oito meses. Resultados de ensaios de caracterização, resistência e obtenção das propriedades hidráulicas dos solos que compõem o maciço estudado são analisados, assim como ensaios realizados com a argamassa de revestimento do talude, ensaios para a análise do funcionamento dos tensímetros e tubos tensiométricos utilizados no monitoramento, e outros ensaios realizados in situ. O monitoramento realizado indicou coerência entre precipitações e variação da poropressão de água, e variação do nível dágua do terreno, em ambos os tipos de revestimento superficial, vegetação natural e argamassa, nos dois tipos de solo presentes no maciço. Análises de estabilidade do talude indicaram o efeito do tipo de revestimento superficial e das variações sazonais de poro-pressão de água no fator de segurança ao escorregamento do talude. / Slopes formed by unsaturated soils are very common in Brazil. In these cases porewater pressure contribute for the slope stability behavior. This work aims at evaluating the effects of types of superficial coating on the profile of pore-water pressure changes, due to flow generated by precipitation, evaporation and evapotranspiration, and consequently on the stability of a experimental slope. It is presented here the geological-geotechnical, geomorfological, climatic and pluvial characterizations of the experimental field located in the east zone of São Paulo/SP, where have been installed and monitored tensiometers, pluviometer and groundwater level measurer during eight months. Results of tests of characterization, shear strength, and for obtaining the hydraulic properties of the in situ soils are analyzed, as well as the tests carried out with de mortar applied over the slope, as well as the functionality tests for the tensimeters and tensiometric tubes used on the monitoring, as well as other in situ tests. Monitoring indicated coherence between precipitation and change in pore-water pressure profile, and groundwater level, in both types of superficial coatings, natural vegetation and mortar, and in both types of in situ soils. Stability analyzes indicated the effect of the type of superficial coating and of the variation of pore-water pressure profile, during the experiment, on the factor of safety of the experimental slope.

A presente pesquisa apresenta resultados de uma série de ensaios de palheta de laboratório, com a finalidade de determinar a resistência não drenada de um solo residual compactado. Durante o ensaio foram realizadas medições continuas de sucção com uso de um tensiômetro de alta capacidade, disposto na base dos corpos de prova, sendo este procedimento inédito. O objetivo secundário do estudo é a avaliação de aspectos relacionados com a variação da resistência e sucção quando a distância do tensiômetro de alta capacidade é modificada com relação à superfície inferior do plano de ruptura pré-estabelecido. Para a realização destes experimentos foram modificados e adaptados equipamentos de laboratório. O estudo foi realizado com um solo residual de gnaisse compactado obtido do antigo campo experimental da Escola Politécnica da Universidade de São Paulo. O estudo constata que o valor medido da resistência não drenada é afetado pela proximidade do tensiômetro a palheta. / This research presents results of a series of mini-vane tests in order to determine the undrained shear strength of a residual compacted soil. During the tests and for the first time, continuous measurement of suction has been made using a high capacity tensiometer placed at the base of the specimen. The secondary aim of this study is to evaluate aspects related to resistance and suction variation when the distance of the high capacity tensiometer is modified in relation to the lower pre-set failure surface. For this reason laboratory equipments were modified and adapted in order to perform the study. The tests were performed with a compacted residual soil of gneiss obtained from the experimental site of the Polytechnical School of the University of São Paulo. The study showed that the undrained shear strength is affected when the vane are closer to the tensiometer.