Dissertations / Theses on the topic 'SOIL-WATER CHARACTERISTICS CURE'

Soil-water characteristic curve (SWCC) also known as water retention curve is an integral part of unsaturated soil mechanics. SWCC is a constitutive relation in unsaturated soil mechanics where soil suction is related to water content. Wetting SWCCs were determined for different sand-bentonite clay mixtures. With the help of the Van-Genuchten equation, acquired test data were fitted. Wetting SWCC can be related to flow of water through unsaturated zones of soil from the groundwater table to the ground surface. Negative column test was employed to determine SWCC since it is fairly simple and simulates the actual field conditions. In the present paper, different soil samples, where sand is mixed with varying proportions of bentonite clay are considered, for determining wetting SWCC. Finer the soil particle, higher will be the soil suction for a given water content. Hence, as the content of clay increases, SWCC slightly shifts towards the right, indicating the increment in soil suction. In turn, water entry value(WEV) also shoots up.

The one-dimensional (1-D) potential heave (or swell strain) of expansive soil is conventionally estimated using the swelling pressure and swelling index values which are determined from different types of oedometer test results. The swelling pressure of expansive soils is typically measured at saturated condition from oedometer tests. The experimental procedures of oedometer tests are cumbersome as well as time-consuming for use in conventional geotechnical engineering practice and are not capable for estimating heave under different stages of unsaturated conditions. To alleviate these limitations, semi-empirical models are proposed in this thesis to predict the variation of swelling pressure of both compacted and natural expansive soils with respect to soil suction using the soil-water characteristic curve (SWCC) as a tool. An empirical relationship is also suggested for estimating the swelling index from plasticity index values, alleviating the need for conducting oedometer tests. The predicted swelling pressure and estimated swelling index are then used to estimate the variation of 1-D heave with respect to suction for expansive soils by modifying Fredlund (1983) equation. The proposed approach is validated on six different compacted expansive soils from US, and on eight field sites from six countries; namely, Saudi Arabia, Australia, Canada, China, US, and the UK. The proposed simple techniques presented in this thesis are friendly for the practitioners for using when estimating the heave in unsaturated expansive soils.

The importance of applying unsaturated soil mechanics concepts to geotechnical engineering design has been widely recognized. Soil water characteristic curve (SWCC) and hydraulic conductivity function (HCF) are vital soil properties that govern engineering behavior of unsaturated soils. In this study, a transient water release and imbibitions method (TRIM) is used to measure the SWCC and HCF under drying and wetting states, which accommodates integrated experimental and modeling techniques. The results of saturated hydraulic conductivity tests through flexible wall method are then used as input parameters for simulating experimental data. In general, the model provides a satisfactory fit to experimental data. Soil water characteristic curves (SWCCs) and hydraulic conductivity functions (HCFs) are presented for a variety of soils that were prepared at different molding water contents and compactive efforts. The influences of dry density, molding water content, and hysteresis have been investigated. Dry density affects soil-water characteristic in terms of its air-entry value (AEV), rate of drying, and size of the hysteresis loop. The test results indicate that the SWCC and HCF obtained in terms of volumetric water content is more sensitive to the changes in dry density than molding water content. Based on cohesive soil results, some statistical relations are proposed to estimate wetting-path SWCC and HCF parameters from more easily measured drying curves. Changes in the van Genuchten's fitting parameters and residual volumetric water content are investigated for both drying and wetting conditions, with changes in the kaolin clay content.
Master of Science

The soil water characteristics curve (SWCC) of a soil plays an important role in study of unsaturated soil mechanics. The behavior of unsaturated soil is a complex phenomenon to understand and the direct measurement of unsaturated soil properties in laboratory or in field is costly and time consuming. Knowing the SWCC of a soil is useful in estimating the unsaturated property of a soil, which is close to the natural soil conditions and can be used in effective design procedure. The present study deals with the effect of plasticity and initial compaction conditions of a soil in the SWCC by using SWC-150 (Fredlund SWCC device) and WP4C dewpoint potentiometer. The test data obtained from both the device were best fitted using Fredlund and Xing (1994) equation (FX), Van Genutchen (1980) equation (VG), Burdine (1958) equation, and Mualem (1976) equation.

Previous studies of agricultural conditions in the Mekong Delta (MD) have identified soil compaction as an obstacle to sustainable production. A conceptual model for soil formation was presented to demonstrate the link between soil hydrology and plant response. Detailed studies of soil moisture dynamics in agricultural fields were conducted using a dynamic process-orientated model. Pressure head and water flow were simulated for three selected sites during a year for which empirical data were available. Daily meteorological data were used as dynamic input and measured pressure head was used to estimate parameter values that satisfied various acceptance criteria. The Generalised Likelihood Uncertainty Estimation (GLUE) approach was applied for calibration procedures with 10,000 runs, each run using random values within the chosen range of parameter values. To evaluate model performance and uncertainty estimation, re-sampling was carried out using coefficient of determination (R2) and mean error (ME) as the criteria. Correlations between parameters and R2 (and ME) and among parameters were also considered to analyse the relationship of the selected parameter set in response to increases/decreases in the acceptable simulations. The method was successful for two of the three sites, with many accepted simulations. For these sites, the uncertainty was reduced and it was possible to quantify the importance of the different parameters.

 

Para a determinação do comportamento de um solo não saturado, é necessária a identificação da sua curva característica, que representa a capacidade de armazenamento de água pelo solo em função do valor de sucção imposto. Quando este solo é submetido a algum processo de contaminação, a sua estrutura interna pode ser alterada por processos físico-químicos, modificando, por conseqüência, o seu comportamento. Esta dissertação propõe uma metodologia de ensaio para a determinação de curvas características de sucção total em um solo artificialmente contaminado com diferentes teores de óleo diesel. O programa experimental proposto consiste basicamente na realização do método do papel filtro, através da técnica sem contato entre a amostra e o papel, com algumas modificações em relação às metodologias anteriormente descritas na literatura geotécnica. Foram também executados ensaios para controle e quantificação da evaporação do contaminante ao longo do tempo, e sua possível absorção pelo papel filtro utilizado. Além disso, foram realizados ensaios para a caracterização física, mineralógica e química do solo, antes e após a adição do óleo, com o intuito de constatar as alterações causadas pela contaminação. O material estudado é constituído por sedimentos coluvionares provenientes de arenito da Formação Botucatu, sendo que sua curva característica, sem contaminação, já foi determinada em um estudo anterior, através do método do papel filtro com contato. Para possibilitar comparações entre estes resultados, foram medidos também alguns pontos em amostras não contaminadas, através da técnica proposta nesta dissertação. Estes apresentaram uma satisfatória concordância em relação à curva anteriormente ajustada. Na análise das curvas características do solo contaminado com 2%, 5%, 10% e 15% de óleo diesel, constatou-se a permanência do formato bimodal, sugerindo que a microestrutura e a macroestrutura continuam influenciando na entrada e saída de água do meio. Entretanto, foram identificadas alterações na forma da curva e na extensão dos patamares resultantes, em relação à curva característica sem contaminação, assim como as diferentes localizações dos valores de entrada de ar. Foi verificado que, conforme o aumento do teor de contaminante, há uma gradual tendência ao formato unimodal da curva característica, induzindo a um comportamento de solo tipicamente granular. Este fato foi comprovado nos resultados de microscopia eletrônica, onde se verifica que, com teores menores de óleo, a estrutura do solo encontra-se mais fechada e, à medida que este teor aumenta, a estrutura torna-se mais porosa. Os tempos de equalização para o método de ensaio proposto variaram entre 7 e 30 dias, conforme o nível de sucção da amostra. A avaliação da histerese revelou que, com o aumento do teor de contaminante, há uma pequena redução deste fenômeno. Além disso, os ensaios complementares comprovaram a existência de uma pequena porcentagem de evaporação do óleo diesel, assim como a absorção do mesmo pelo papel filtro, que se apresentou praticamente nula.
The unsaturated soil behavior can be determined through its soil-water characteristic curve, which represents the capacity of the soil to store water when submitted to different suction levels. When this soil is contaminated, its internal structure can be modified according to physical and chemical processes, thus changing the initial behavior. This dissertation proposes a test methodology to determine the total-suction soil-water characteristic curves of a contaminated soil at different diesel oil contents. The experimental program consisted of using the filter-paper method without contact between the sample and the paper, but with some modifications in relation to previously studied techniques. Some control tests were also carried out to check oil evaporation and its absortion by the filter paper. Besides, the samples were submitted to physical, mineralogical and chemical characterization, before and after contamination, to verify the possible changes. The studied material is a colluvium soil, constituted basically by sandstone, from the Botucatu Formation. This soil was previously studied by the filter-paper method with contact, and its soil water characteristic curve without contamination was already known. To compare the results, the proposed test methodology was also performed with non contaminated samples, showing a satisfactory agreement with the initial curve. The soil-water characteristic curves of this soil with a diesel oil content of 2%, 5%, 10% and 15% showed a "saddle" shape, indicating that both the microstructure and the macrostructure were influenced by the entrance and exit of water through the soil. However, the shape of the curve and the extent of its plateau changed according to the level of contamination. Increasing the oil content, the curve tends to a unimodal shape, with a behavior similar to granular soils. This statement was proved by the microstruture photographs, which showed an increase of sample porosity due to the increase of oil content. The time required to reach suction equilibrium during the tests varied between 7 to 30 days, according to the initial water content of the samples. The observed hysteresis had a small reduction with the increase of oil content. The control tests proved that oil evaporation and its absortion by the filter paper were insignificant in the whole test program.

In many situations, the upper layers of soil above the ground water table are in a state of unsaturated condition. Although unsaturated soils are found throughout the world, they are predominant in arid or semi-arid regions. In these areas, the soil water characteristic curve (SWCC) which relates the water content to the matric suction could be used as key tool to implement the mechanics of unsaturated soils into the designs of geotechnical structures such as dams, embankments, pavements, canals, and foundations. Several experimental techniques are available for determining the SWCC in a laboratory environment. However, these experimental techniques are expensive, time consuming typically requiring days or weeks, depending on the soil type, and demanding intricate testing equipment. Due to these reasons, there has been a growing interest to find other means for estimating SWCC and encourage the adoption of unsaturated soils mechanics in geotechnical engineering practice. Several methods exist to indirectly estimate the SWCC from basic soil properties. Some may include statistical estimation of the water content at selected matric suction values, correlation of soil properties with the fitting parameters of an analytical equation that represents the SWCC, estimation of the SWCC using a physics-based conceptual model, and artificial intelligence methods such as neural networks or genetic programming. However, many studies have shown that environmental effects such as temperature, soil structure, initial water content, void ratio, stress history, compaction method, etc. can also affect the SWCC. This means that the estimation SWCC from set of conditions may not reliably predict the SWCC in other conditions. Due to this reason, it is crucial for engineers involved with unsaturated soils to take into account all the factors that influence the SWCC. The two key objectives of the present thesis are the development of a method based on first principles, using the capillary rise theory, to predict the variation of the SWCC as a function of temperature, as well as developing a technique for the prediction of the fixed parameters of a well-known function representing the SWCC based on basic soil properties together with the moisture profile of a soil column subjected to a known temperature gradient. A rational approach using capillary rise theory and the effect of temperature on surface tension and liquid density is developed to study the relation between temperature and the parameters of the Fredlund and Xing (1994) equation. Several tests, using a Tempe cell submerged in a controlled temperature bath, were performed to determine the SWCC of two coarse-grained soils at different temperatures. A good comparison between the predicted SWCC at different temperatures using the proposed model and the measured values from the Tempe cell test results is achieved. Within the scope of this thesis, a separate testing program was undertaken to indirectly estimate the SWCC of the same two coarse-grained soils from the measurement of their steady state soil-moisture profile while subjected to a fixed temperature differences. The water potential equation in the liquid and vapor phases is used to analyses the steady state flow conditions in the unsaturated soil. A good comparison is obtained for the SWCC estimated using this technique with the SWCC measured used a Tempe cell submerged in a controlled temperature bath. The results of this study indicate that knowledge of the moisture content of a soil specimen under a constant thermal gradient and basic soil properties can be used to estimate the SWCC of the soil at the desired temperature.

A mecânica dos solos não saturados tem se tornado um importante tema de pesquisas dedicadas a entender o comportamento dos solos não saturados e otimizar sua utilização em várias obras civis. A curva de retenção de água, definida como a relação entre a sucção e a quantidade de água presente no solo, é considerada um elemento chave na interpretação do comportamento e propriedades dos solos não saturados tais como a condutividade hidráulica e a resistência ao cisalhamento. Este trabalho apresenta a estrutura de um banco de dados projetado para armazenar informações de solos brasileiros com enfoque nas características de retenção de água. O banco de dados inclui a curva de retenção e os parâmetros de ajuste das equações de van Genuchten (1980) e Fredlund & Xing (1994), assim como informações das características dos solos como índices físicos, classificações dos solos, análises granulométricas, índices de consistência e localização e estado da amostra. Além da estimativa da função condutividade hidráulica, o banco de dados oferece duas ferramentas que permitem a pesquisa rápida ou detalhada das informações e os dados armazenados podem ser mostrados na tela ou em relatórios impressos
Unsaturated soil mechanics has become an important subject of research devoted to understand the behavior of unsaturated soils and optimize their use in several civil works. The soil-water characteristic curve, defined as the relationship between the suction and the amount of water present in the soil, is considered as the key in the interpretation of the behavior and properties of unsaturated soils, such as the hydraulic conductivity and the shear strength. This paper presents the structure of a database designed to store information of brazilian soils with focus in the characteristics of water retention. The database includes the retention curves and the parameters of adjusted van Genuchten and Fredlund & Xing equations and also information of soil characteristics such as physical indexes, soil classifications, particle-size analysis, consistency indexes and location and kind of used samples. Beyond the estimate of hydraulic conductivity, the database presents two search tools that allow for quick and detailed recovering of information and stored data can be displayed on screen or in printed reports

Esta tese apresenta um estudo sobre a resistência ao cisalhamento e a condutividade hidráulica de dois solos coluvionares não saturados situados na divisa dos estados do Rio Grande do Sul e Santa Catarina, em um dos trechos do Gasoduto Bolívia-Brasil. Esses solos são constituídos por sedimentos oriundos da Formação Serra Geral (basalto – Solo RO) e da Formação Botucatu (arenito – Solo AV). O trabalho de pesquisa realizado com esses solos tem seu enfoque dividido em duas partes principais: (1) obtenção direta da resistência ao cisalhamento e da função condutividade hidráulica em diferentes níveis de sucção, e (2) previsão indireta dessas propriedades a partir da determinação da curva característica do solo e de parâmetros geotécnicos saturados. As curvas características dos solos AV e RO, nas condições indeformada e remoldada (sem e com secagem prévia do solo), foram obtidas pelo uso combinado do método do papel filtro e da placa de sucção. Para as condições indeformada e remoldada sem secagem prévia, essas curvas exibiram um formato bimodal. A dessaturação é controlada pelos macroporos, para baixas sucções, e pelos microporos, para altas sucções. Para valores de sucção intermediários, praticamente não ocorre remoção de água do solo, devido, provavelmente, à ausência de poros com tamanho intermediário. Já as curvas características das amostras remoldadas com secagem prévia do solo tendem a apresentar um formato mais próximo do unimodal. A influência do índice de vazios inicial e da história de umedecimento e secagem no formato da curva é também discutida. A resistência ao cisalhamento dos solos estudados foi determinada em laboratório através de ensaios de cisalhamento direto convencionais e com sucção controlada. Os resultados, obtidos para amostras indeformadas e remoldadas sem secagem prévia, permitiram a determinação dos parâmetros de resistência ao cisalhamento c’, f’ e fb. Para determinação direta da função condutividade hidráulica do Solo AV foi construído um permeâmetro triaxial com controle de sucção, baseado no modelo apresentado por Huang et al. (1998). Esse equipamento foi utilizado para determinação da função condutividade hidráulica do Solo AV não saturado, em diferentes trajetórias de umedecimento e secagem. Os resultados evidenciaram que as amostras do Solo AV nas três condições de moldagem - indeformada, remoldada sem e com secagem - tendem a reproduzir o comportamento de dessaturação exibido nas curvas características. A função condutividade hidráulica apresenta inicialmente um decréscimo para sucções até 50 kPa, seguido por um valor praticamente constante, para sucções até 90 kPa.
This thesis presents a study about the shear strength and hydraulic conductivity of two unsaturated colluvium soils situated at the border between the states of Rio Grande do Sul and Santa Catarina, along one of the Bolivia-Brazil Gas Pipeline stretches. These soils are constituted by sediments originated from Serra Geral (basalt – sample RO) and Botucatu formations (sandstone - sample AV). The research performed with these soils had its focus divided in two main parts: (1) direct measurements of shear strength and hydraulic conductivity function at different suction levels and (2) indirect prediction of these properties from the soil-water characteristic curves and saturated geotechnical parameters. The soilwater characteristic curves of AV and RO Samples, in undisturbed and remolded conditions (without and with previous drying), were determined with both the filter-paper technique and the suction-plate technique. The undisturbed and remolded samples without previous drying showed a bimodal shape. The desaturation is controlled by the macropores for low suction values and by the micropores, for higher values. For intermediary suctions values, practically no removal of water from the sample occurs, possibly due to the lack of intermediate pore sizes. The remolded samples with previous drying tend to present a shape close to unimodal. The influences of void ratio and the drying and wetting history in the shape of the soil-water characteristic curve are also discussed. The shear strength of the studied soils was determined with conventional and suction-controlled direct shear tests. The results obtained for undisturbed and remolded samples without previous drying allowed the determination of shear strength parameters c’, f’ e fb. For the direct measurement of hydraulic conductivity function, a flexible-wall permeameter was built, based on the model presented by Huang et al. (1998). This equipment was used for determining the unsaturated hydraulic conductivity function of Sample AV in different drying and wetting paths. The results showed that Samples AV in the three molding conditions - undisturbed and remolded without and with previous drying – reproduced the desaturation behavior showed by the soil-water characteristic curves. The hydraulic conductivity function presents initially a decrease for suctions up to 50 kPa, followed by a practically constant value, for suctions up to 90 kPa.

The objectives of this research were to 1) measure the extent to which water vapor movement results in water accumulation in freezing base materials; 2) evaluate the effect of soil stabilization on water vapor movement in freezing base materials; 3) determine if the corresponding changes in water content are sufficient to cause frost heave during winter; 4) determine if the corresponding changes in water content are sufficient to cause reductions in stiffness during spring; 5) evaluate relationships between selected material properties, freezing conditions, and the occurrence and impact of water vapor movement; and 6) numerically simulate heat and water movement in selected pavement design scenarios. The research involved extensive laboratory and field testing, statistical analyses, and numerical modeling. The results of the laboratory testing, which included gradations, Atterberg limits, soil classifications, specific gravity and absorption values, electrical conductivity values, moisture-density relationships, soil-water characteristic curves, moisture-stiffness curves, hydraulic conductivity values, and frost susceptibility assessments, were used to characterize each material and enable subsequent statistical analyses. Testing of both treated and untreated materials enabled investigation of a wide variety of material properties. The results of the field testing, which included temperature, moisture content, water potential, elevation, and stiffness data over time, provided the basis for comparing pavement sections with and without capillary barriers and established the framework for numerical modeling. In a pavement section with a capillary barrier underlying the base layer, water vapor movement from the subgrade through the capillary barrier may be expected to increase the water content of the base layer by 1 to 3 percent during a typical winter season in northern Utah for base materials similar to those studied in this research. During winter, cold temperatures create an ideal environment for water vapor to travel upward from the warm subgrade soil below the frost line, through the capillary barrier, and into the base material. Soil stabilization can lead to increased or decreased amounts of water vapor movement in freezing base materials depending on the properties of the stabilized soil, which may be affected by gradation, mineralogy, and stabilizer type and concentration. Accumulation of water from long-term water vapor movement into frost-susceptible base materials underlain by a capillary barrier can lead to frost heave of the base layer as it approaches saturation, as water available in the layer can be redistributed upwards to create ice lenses upon freezing. However, the incremental increase in total water content that may occur exclusively from water vapor movement during a single winter season in northern Utah would not be expected to cause measurable increases in thaw weakening of the base layer during spring. Because water in a base layer overlying a capillary barrier cannot drain until nearly reaching positive pore pressures, the base layer will remain indefinitely saturated or nearly saturated as demonstrated in this research. For materials similar to those studied in this research, potentially important material properties related to the occurrence of water vapor movement during freezing include dry density, percent of material finer than the No. 200 sieve, percent of material finer than 0.02 mm, apparent specific gravity, absorption, initial water content, porosity, degree of saturation, hydraulic conductivity, and electrical conductivity. The rate at which water vapor movement occurs is also dependent on the thermal gradient within the given material, where higher thermal gradients are associated with higher amounts of water vapor movement. The numerical modeling supported the field observations that the capillary barrier effectively trapped moisture in the overlying base material, causing it to remain saturated or nearly saturated throughout the monitoring period. Only non-frost-susceptible aggregate base materials should be specified for use in cold climates in conjunction with capillary barriers, and the base material in this case should be assumed to remain in a saturated or nearly saturated condition during the entire service life of the pavement. Further study is recommended on water vapor movement in freezing aggregate base materials.

Orientador: Miriam Gonçalves Miguel
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo
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Resumo: Como ponto de partida, concentra-se esta pesquisa em determinar as relações de teor de umidade (ou grau de saturação) versus o valor da sucção matricial, conhecidas por curvas características de sucção ou curvas de retenção, para o solo da camada superficial do Campo Experimental de Mecânica dos Solos e Fundações da UNICAMP. Esta camada é constituída de uma argila siltoarenosa, porosa, em condição não saturada, laterítica, colapsível e coluvionar de espessura em torno de 6,5m; resultante do alto grau de intemperismo. Na determinação das curvas utilizou-se a técnica do papel filtro, complementando a técnica de translação de eixos, já utilizada para o solo, através do Aparelho de Richards. Os procedimentos foram de secagem e de umedecimento das amostras, permitindo o estudo do fenômeno de histerese, à luz da estrutura e da composição químico-mineralógica do solo. Também foi realizado um monitoramento em campo da variação da sucção matricial ao longo de um ano, para confirmar o fenômeno da histerese que ocorre in situo As curvas de retenção de água forneceram valores de pressão de entrada de ar que variam de 1 à 5 kPa, dependendo da técnica utilizada, lembrando o comportamento de areias, e mostraram que o fenômeno da histerese ocorre de maneira mais acentuada, em solos com poros maiores. Confrontaram-se os resultados obtidos com as diferentes técnicas de realização dos ensaios e analisaram-se as diferenças entre elas.
Abstract: This research focuses in to determine the relationship of moisture content (or degree of saturation) versus the value of the suction matrix, known as soil water characteristic curve (SWCC), to the soil surface layer of the Field Experimental of Soil Mechanics and Foundation of UNICAMP. This profile consists of colluvial, lateritic, porous, on condition unsaturated and collapsible silty clay, with thickness around 6,5m and present on a clayed silt soil, residual of diabase; resulting from the high degree of weathering. To determine the curves, the techniques of filter paper and axis-translation were used, with a Richards equipment, this already used to the soil. The procedures were wetting and drying of the samples, allowing the study of the phenomenon of hysteresis, in the light of the structure and chemical and mineralogical composition of the soil. It was carried out in the field of "tracking a variation of suction matrix over a year, to confirm the phenomenon of hysteresis that occurs in situo The SWCCs supplied values of enter air ranging from 1 to 5 kPa, depending on the technique used, reminding the behaviour of sand, and showed that the phenomenon of hysteresis occurs in a manner more pronounced in soils with pores greater.' Compared the achievements of ,lhe different techniques for conducting the tests and analyzed the differences between them.
Mestrado
Geotecnia
Mestre em Engenharia Civil

Under hösten 2019 har Vattenfall Research & Development byggt en experimentell jordfyllningsdamm i Älvkarleby med dimensionerna 20x15x4 meter. Delar av experimentdammen är konventionellt konstruerade och har installerats med geoteknisk utrustning som utgörs av bland annat inklinometrar och portrycksgivare. Andra delar av experimentdammen har byggts in med defekter som ska representera åldersrelaterade skador eller utförandefel vid konstruktion. Experimentdammen ger möjlighet att under realistiska och kontrollerade förhållanden studera det mekaniska beteendet i samband med fyllning av vatten och vidare drift med hjälp av den geotekniska instrumenteringen samt med stöd av numerisk modellering. I detta examensarbete, som utgör en del av Luleå tekniska universitets forskningsprojekt mot experimentdammen, har experimentdammens beteende i form av deformationer och portryck studerats under uppfyllnad och drift fram till sommaren 2021. Detta har utförts genom simuleringar i det finita elementprogrammet PLAXIS 2D 2019 för en tvärsektion av experimentdammen i plant-deformationstillstånd. Mätpunkterna i modellen har baserats på faktisk placering av den geotekniska instrumenteringen. Den finita elementmodellen av experimentdammen har konstruerats och fyllts med vatten enligt dokumentation från fält. En flödes-deformationsanalys, med den konstitutiva modellen Hardening Soil och den hydrauliska modellen van Genuchten, har tillämpats för att modellera den simultana utvecklingen av portryck och deformationer under uppfyllnad. Materialparametervärden för den finita elementmodelleringen har erhållits från Vattenfall R&D, relevant litteratur och från fält- och laboratorieförsök. I fält har vattenvolymeterförsök utförts på tätkärnan och i laboratoriemiljö har modifierad proctorpackning, dränerade konventionella triaxialförsök, permeabilitetsförsök och övertryckskapillarimeterförsök utförts på tätkärnans material. Resultatet från övertryckskapillarimeterförsök har anpassats mot den hydrauliska modellen van Genuchten för att uppskatta en vattenbindningskurva som beskriver det icke-linjära förhållandet mellan jordens vatteninnehåll och porundertryck, det vill säga det omättade förhållandet. Vattenbindningskurvor för övriga materialzoner har uppskattats baserat på litteratur. Verktyget PLAXIS SoilTest har använts för att optimera materialparametervärden för tätkärnan mot resultat från utförda triaxialförsök. Materialparametrarna E50ref, Eoedref, Eurref, m, c, och ϕ har optimerats fram till brott i triaxial belastning. En känslighetsanalys har utförts för reduktion av filterzonernas och stödfyllningens styvhetsmoduler och deras inverkan på horisontella deformationer i dammkroppen under uppfyllnad. Känslighetsanalysen indikerar att finfiltrets styvhetsmoduler har störst inverkan och grovfiltrets styvhetsmoduler har minst inverkan på de horisontella deformationerna. Studiens resultat visar att magnituden av horisontella och vertikala deformationer kommer vara som störst i den övre delen av dammkroppen och uppgår där till 3,5 respektive 4,0 mm. Dammkroppens huvudsakliga rörelse kommer vara i nedströms riktning och det observerades hur en kontaktzon mellan uppströms filterzon och tätkärnan utgör en gräns för riktning av deformationer. Faktiskt uppmätta rörelser i installerade inklinometrar kunde inte jämföras mot deformationer i den finita elementmodellen eftersom författarens tolkning indikerar på att botten av inklinometrarna har rört på sig, och mätpunkterna i botten av modellen är fixerade. Modellen visar hur en fördröjd utveckling av vattenmättnad sker genom tätkärnan, där uppströms sida av tätkärnan reagerar snabbare på förändringar i vattennivå jämfört med nedströms sida av tätkärnan som uppvisar en fördröjd respons. Vid en sänkning av vattennivån observerades hur tätkärnan håller kvar vatten ovan portryckslinjen medan de grövre materialen dränerar i takt med vattennivåns sänkning. Utvecklingen av de simulerade portrycken i modellen under uppfyllnad och drift överensstämmer bra med de uppmätta portrycken i experimentdammen, när portrycken är positiva. Det observeras hur den finita elementmodellen överskattar negativa portryck (porundertryck). Portrycken i modellen når ett stadigt tillstånd ungefär 115 dagar efter att fyllningen av vatten påbörjats. Den finita elementmodellen lyckas att återge det teoretiska beteendet av jordfyllningsdammar under fyllning i form av huvudsakliga riktningar av deformationer och utveckling av vattenmättnad i tätkärnan. Denna studie bidrar till en djupare förståelse för experimentdammens, och i allmänhet jordfyllningsdammars, mekaniska beteende under uppfyllnad. Resultaten från den finita elementmodellen kan ur ett dammsäkerhetsperspektiv användas för erhålla indikationer på utvecklingen av deformationer, portryck och vattenmättnadsgrad i jordfyllningsdammar under uppfyllnad, och även under en tillfällig sänkning av vattennivån under den första fyllningen. Studien ger också indikationer på vilka materialparametrar som är viktiga vid numerisk modellering av mekaniskt beteende i jordfyllningsdammar.
During the autumn of 2019, Vattenfall Research & Development constructed an experimental embankment dam in Älvkarleby with the dimensions 20x15x4 metres. Parts of the experimental dam are conventionally constructed and have been equipped with geotechnical instrumentation which consist of, among other things, inclinometers and pore pressure transducers. Other parts of the experimental dam have built in defects to represent age-related damages or execution errors during construction. The experimental embankment dam provides the opportunity to, under realistic and controlled conditions, study the mechanical behaviour during filling of water and operation by means of the geotechnical instrumentation and the use of numerical modelling. In this master’s thesis, which forms part of Luleå University of Technology’s research project towards the experimental dam, the behaviour of the experimental dam in terms of deformations and pore pressures have been studied during filling and operation until the summer of 2021. This has been performed by simulations in the finite element program PLAXIS 2D 2019 for a cross section of the experimental dam under plane-strain conditions. Measuring points in the model have been based on the actual location of the geotechnical instrumentation. The finite element model of the experimental dam has been constructed and filled according to documentation from field. A fully-coupled flow deformation analysis, with the constitutive model Hardening Soil and hydraulic model van Genuchten, has been utilised to model the simultaneous development of pore pressure and deformations during filling. Values of material parameters for the finite element modelling have been received from Vattenfall R&D, relevant literature and from field- and laboratory tests. In the field, balloon tests have been performed on the core material. In laboratory environment, modified proctor compaction tests, drained conventional triaxial tests, permeability tests and pressure plate tests have been performed on the core material. Results from the pressure plate tests have been adapted to the hydraulic model van Genuchten to estimate a soil-water characteristic curve in order to describe the non-linear relation between the water content and suction in the soil, i.e. unsaturated conditions. Soil-water characteristic curves for the other material zones have been estimated based on literature. The tool PLAXIS SoilTest has been used to optimise material parameter values of the core against the results from conducted triaxial tests. The material parameters E50ref, Eoedref, Eurref, m, c, and ϕ have been optimised until failure in triaxial loading. A sensitivity analysis has been carried out, by reducing stiffness moduli of the filter zones and the shoulder material, to investigate the influence on horizontal deformations in the dam body during filling. The sensitivity analysis indicates that the stiffness moduli of the fine filter have the largest impact and the stiffness moduli of the coarse filter have the least impact on the horizontal deformations. The results of the study show that the magnitude of horizontal and vertical deformations will be largest in the upper part of the dam body and amounts to 3.5 and 4.0 mm, respectively. The main movement of the dam body will be in the downstream direction and it was observed how a contact zone between the upstream filter zone and the core forms a boundary for direction of deformations. Actual measured movements in the installed inclinometers could not be compared to deformations in the finite element model because the author’s interpretation indicates that the bottom of the inclinometers have moved, and the measuring points at the bottom of the model are fixed. The model shows how a delayed development of saturation occur through the core, where the upstream side of the core responds more quickly to changes in water level compared with the downstream side of the core which show a delayed response. At a lowering of the water level, it was observed how the core retains water above the phreatic line while the coarser materials drain as the water level decreases. Development of the simulated pore pressures in the model during filling and operation corresponds well with the measured pore pressures in the experimental dam, when the pore pressures are positive. It is observed how the finite element model overestimates negative pore pressures (suction). The pore pressures in the model reaches a steady state approximately 115 days after filling of water started. The finite element model succeeds in reproducing the theoretical behaviour of embankment dams during filling in terms of main directions of deformations and development of saturation in the core. This study contributes to a deeper understanding of the experimental dam, and in general mechanical behaviour of embankment dams during filling. The results from the finite element model can be used from a dam safety perspective to obtain indications on the development of deformations, pore pressures and degree of saturation in embankment dams during filling, and also for a temporary lowering of the water level during the first filling. The study also provides indications of which material parameters that are of importance in numerical modelling of mechanical behaviour in embankment dams.

Reservoir release patterns are determined by a number of purposes, the most fundamental of which is to manage water resources for human use. Managing our water resources means not only controlling the water in reservoirs but also determining the optimum release rate taking into account factors such as reservoir stability, power generation, water supply for domestic, industrial, and agricultural uses, and the river ecosystem. However, riverbank stability has generally not been considered as a factor, even though release rates may have a significant effect on downstream riverbank stability. Riverbank retreat not only impacts land properties but also damages structures along the river such as roads, bridges and even buildings. Thus, reservoir releases need to also take into account the downstream riverbank stability and erosion issues. The study presented here investigates the riverbank stability and erosion at five study sites representing straight as well as inside and outside channel meander bends located on the lower Roanoke River near Scotland Neck, North Carolina. Extensive laboratory and field experiments were performed to define the hydraulic and geotechnical properties of the riverbank soils at each site. Specifically, soil water characteristic curves were determined using six different techniques and the results compared to existing mathematical models. Hydraulic conductivity was estimated using both laboratory and in situ tests. Due to the wide range of experimentally obtained values, the values determined by each of the methods was used for transient seepage modeling and the modeling results compared to the actual ground water table measured in the field. The results indicate that although the hydraulic conductivities determined by in situ tests were much larger than those typically reported for the soils by lab tests, numerical predictions of the ground water table using the in situ values provided a good fit for the measured ground water table elevation. Shear strengths of unsaturated soils were determined using multistage suction controlled direct shear tests. The test method was validated, and saturated and unsaturated shear strength parameters determined. These parameters, which were determined on the basis of results from both laboratory and field measurements, and the associated boundary conditions, which took into account representative flow rates and patterns including peaking, drawdown and step-down scenarios, were then utilized for transient seepage analyses and slope stability analyses performed using SLIDE, a software package developed by Rocscience. The analyses confirmed that the riverbanks are stable for all flow conditions, although the presence of lower permeability soils in some areas may create excess pore water pressures, especially during drawdown and step-down events, that result in the slope becoming unstable in those locations. These findings indicate that overall, the current reservoir release patterns do not cause adverse impacts on the downstream riverbanks, although a gradual drawdown after a prolonged high flow event during the wet season would reduce unfavorable conditions that threaten riverbank stability.
Ph. D.

This research project has led to the development of a new approach to assess the saturated and unsaturated properties of soil material subjected to slaking. Constant saturation along with overburden pressure resulted in a larger vertical deformation ofInvestigation on geotechnical engineering properties of coal mine spoil subjected to slaking the slaking chambers; which is indicative of slaking, these results indicate that material slaking was occurring due to saturation and overburden pressure. This will have a substantial benefit to the mining operations with distinctive interest associated to safety of the mine spoil slopes, limiting failures to protect workers, equipment, and operational costs.

Cette thèse concerne la caractérisation expérimentale d’un sable limoneux provenant du barrage de Livet – Gavet (38) dans le cadre du projet ANR TerreDurable avec plusieurs objectifs : 1- Caractériser au travers d’essais de laboratoire le comportement hydromécanique d’un sable fin limoneux (sol A1 dans la classification GTR) en fonction de son état de saturation. Lors de cette étude, un accent particulier est porté sur la caractérisation de ce comportement dans le domaine proche de la saturation. 2- Interpréter le comportement hydrique du matériau sur chemin de drainage – imbibition en relation avec l’analyse de sa microstructure. 3- Fournir d’un point de vue général une base de données et d’analyses exhaustive permettant le développement et la calibration de modèles de comportement des sols fins proches de la saturation, en particulier en considérant des chemins de chargement hydromécanique complexes. Pour l’ensemble de cette étude, le matériau est considéré sous deux états : soit à l’état de pâte (matériau normalement consolidé) préparée à une teneur en eau proche de la limite de liquidité, soit sous forme compactée (matériau sur-consolidé) à différentes énergies de compactage et différentes teneurs en eau initiales
This thesis concerns the experimental characterization of a silty sand from the Livet - Gavet dam (38) as part of the ANR TerreDurable project, for following objectives: 1- Through laboratory tests, characterize the hydro-mechanical behaviour of a fine silty sand (Type A1 in the GTR classification) according to its saturation state. In this study, particular emphasis is placed on the characterization of this behaviour in the near-saturated domain. 2- Interpret the water behaviour of material on the drainage - imbibition cycles, in relation to the analysis of its microstructure. 3- From a general point of view, provide a comprehensive database and analysis allowing the development and calibration of models of near-saturated fine soil's behaviour, in particular, by considering complex hydro-mechanical loading paths. For all tests in this study, the material is considered in two states: either in the state of paste (normally consolidated material) prepared at water content close to the limit of liquidity, or in compacted state (over consolidated material) at different compaction energies and different initial water contents

Nas últimas décadas, teorias têm sido formuladas para interpretar o comportamento de solos não saturados e estas têm se mostrado coerentes com resultados experimentais. Paralelamente, várias técnicas de campo e de laboratório têm sido desenvolvidas. No entanto, a determinação experimental dos parâmetros dos solos não saturados é cara, morosa, exige equipamentos especiais e técnicos experientes. Como resultado, essas teorias têm aplicação limitada a pesquisas acadêmicas e são pouco utilizados na prática da engenharia. Para superar este problema, vários pesquisadores propuseram equações para representar matematicamente o comportamento de solos não saturados. Estas proposições são baseadas em índices físicos, caracterização do solo, em ensaios convencionais ou simplesmente em ajustes de curvas. A relação entre a umidade e a sucção matricial, convencionalmente denominada curva característica de sucção do solo (SWCC) é também uma ferramenta útil na previsão do comportamento de engenharia de solos não saturados. Existem muitas equações para representar matematicamente a SWCC. Algumas são baseadas no pressuposto de que sua forma está diretamente relacionada com a distribuição dos poros e, portanto, com a granulometria. Nestas proposições, os parâmetros são calibrados pelo ajuste da curva de dados experimentais. Outros métodos supõem que a curva pode ser estimada diretamente a partir de propriedades físicas dos solos. Estas propostas são simples e conveniente para a utilização prática, mas são substancialmente incorretas, uma vez que ignoram a influência do teor de umidade, nível de tensões, estrutura do solo e mineralogia. Como resultado, a maioria tem sucesso limitado, dependendo do tipo de solo. Algumas tentativas têm sido feitas para prever a variação da resistência ao cisalhamento com relação a sucção matricial. Estes procedimentos usam, como uma ferramenta, direta ou indiretamente, a SWCC em conjunto com os parâmetros efetivos de resistência c e . Este trabalho discute a aplicabilidade de três equações para previsão da SWCC (Gardner, 1958; van Genuchten, 1980; Fredlund; Xing, 1994) para vinte e quatro amostras de solos residuais brasileiros. A adequação do uso da curva característica normalizada, proposta por Camapum de Carvalho e Leroueil (2004), também foi investigada. Os parâmetros dos modelos foram determinados por ajuste de curva, utilizando técnicas de problema inverso; dois métodos foram usados: algoritmo genético (AG) e Levenberq-Marquardt. Vários parâmetros que influênciam o comportamento da SWCC são discutidos. A relação entre a sucção matricial e resistência ao cisalhamento foi avaliada através de ajuste de curva utilizando as equações propostas por Öberg (1995); Sällfors (1997), Vanapalli et al., (1996), Vilar (2007); Futai (2002); oito resultados experimentais foram analisados. Os vários parâmetros que influênciam a forma da SWCC e a parcela não saturadas da resistência ao cisalhamento são discutidos.
In the last decades, theories have been formulated to interpret the behavior of unsaturated soils and found to be consistent with the experimental response. Besides, several techniques for field and laboratory testing have been developed, as well. However, the experimental determination of unsaturated soil parameters is costly, time-consuming, requires particular test equipments and experienced technicians. As a result, these theories application are limited to academic researches and are barely used in engineering practice. To overcome this issue, several researchers proposed equations to mathematically represent the experimental behavior unsaturated soils. These propositions are based on physical indexes, soil characterization, and current laboratory tests or simply curve fitting. The relationship of soil-water content and matric suction, conventionally referred to as the soil-water characteristic curve (SWCC) is also useful tool in the prediction of the engineering behavior of unsaturated soils. There are many equations to mathematically represent SWCC. Some are based on the assumption that its shape is directly related to the pore distribution, and, therefore, the grain size distribution. In these propositions the parameters are calibrated by curve adjustment of the experimental data. Others assume that the curve can be directly estimated from physical properties of soils. These proposals are simple and convenient for practical use, but are substantially incorrect since they disregard the influence of moisture content, stress level, soil structure and mineralogy. As a result, most of them have limited success depending on soil types. Some attempts have also been made to predict the variation of the shear strength with respect to matric suction. These procedures use SWCC as a tool either directly or indirectly along with the saturated strength parameters c and . This work discusses the applicability of three SWCC equations (Gardner, 1958; van Genuchten, 1980; and Fredlund and Xing, 1994) for twenty four residual soils from Brazil. The suitability of the normalized soil-water characteristic curve, proposed by Camapum de Carvalho and Leroueil (2004), was also investigated. Models parameters were determined by curve fitting, using inverse problem techniques; two optimization methods were used: Genetic Algorithm (GA) and Levenberq-Marquardt method. Several parameters that influence the SWCC behavior are discussed, as well. The relationship between matric suction and shear strength was evaluated by curve fitting using the equations proposed by Öberg and Sällfors (1995, 1997), Vanapalli et al., (1996), Vilar (2007) and Futai (2002); eight experimental results were analyzed. Several parameters that influence the SWCC behavior and the unsaturated shear strength are discussed, as well.

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The hydraulic behavior of a tropical and unsaturated soil profile of Aparecida de Goiânia-GO is presented. The main objective of this research was to contribute to the understanding of hydraulic properties of a tropical soil, with special emphasis on the soil-water characteristic curves and its hysteresis. The research work done was divided into two main parts: physical, chemical and mineralogical characterization; and hydraulic behavior for the unsaturated condition. The characterization tests indicate that the soil profile studied is formed by two horizons. The top layer of 1,50 m comprised of transported material and a bottom layer comprised of young residual soil. The results of particle size analysis have shown that the various sample preparation conditions (i.e., with or without drying, chemical and physical disaggregation) produce different grain-size distribution curves. A varying state of disaggregation can be achieved, that state being dependent on the stability of the soil aggregates. A fairly good correspondence between conventional hydrometer and laser diffraction analysis was achieved, considering supposedly equivalent aggregation conditions. The soil-water characteristic curve (SWCC) was measured for both the natural and the soil reconstituted by mud consolidation. The role played by the soil fabric on the hydraulic behavior of the soil was analyzed. The SWCC was obtained for drying, wetting, and mixed paths, both in terms of total and matric suction. It was determined that the natural and reconstituted soils have distinct SWCCs. The disaggregation achieved with the reconstituted soil results in higher air-entry values and a unimodal SWCC, even when the natural soil presents a bimodal SWCC. Therefore, the pore-size distribution if affected by the different soil structures. The procedure for wetting and drying soil samples used along with the filter paper technique resulted in a number of SWCCs showing absence of hysteresis. The study of the moisture content along the specimen s heights revealed non-homogeneous moisture content distributions, even after 14 day of equilibrium of water potential. It was concluded that it is the very existence of SWCC hysteresis, along with a not sufficiently slow wetting and drying from the specimen surface that results in a non-homogeneous moisture content.
Um estudo do comportamento hidráulico de um perfil de solo tropical e não saturado de Aparecida de Goiânia-GO é apresentado nesta dissertação. O principal objetivo desta pesquisa foi contribuir para o entendimento das propriedades hidráulicas do solo, com especial ênfase na curva característica do solo e na sua histerese. O trabalho teve seu enfoque dividido em duas partes: caracterização física, química e mineralógica do perfil; e comportamento hidráulico do solo na condição não saturada. A partir da caracterização do solo, verificou-se que o perfil estudado se divide em dois extratos, um superior de 1,50 m de material transportado e um inferior residual jovem. Os resultados dos ensaios de granulometria mostraram que as várias combinações de preparação (i.e., com ou sem secagem prévia, desagregação química e desagregação física), produzem curvas granulométricas distintas. Variados graus de desagregação podem ser atingidos, sendo estes dependentes do grau de estabilidade das agregações do solo. Obteve-se uma boa correspondência entre a granulometria convencional e aquela utilizando o granulômetro a laser, para condições de desagregação supostamente equivalentes. A curva característica foi determinada tanto para o material natural, quanto para o solo reconstituído por adensamento a partir do estado de lama. Desta forma, procurou-se verificar o papel da estrutura no comportamento hidráulico do solo. As curvas características foram obtidas em trajetórias de secagem, molhagem, e mistas, tanto em termos de sucção matricial, quando de sucção total. Observou-se que o solo natural possui curvas características distintas do solo reconstituído. A desestruturação do solo reconstituído resulta em um maior valor de entrada de ar e uma curva característica unimodal, mesmo quando o material natural apresenta curva bimodal. Pode-se concluir que a distribuição de poros do material natural é afetada pela estruturação do solo. O procedimento de umedecimento e secagem utilizado com o método do papel filtro resultou em algumas curvas características com ausência de histerese. O estudo da distribuição da umidade ao longo da altura dos corpos de prova revelou que não se obteve umidades homogêneas, mesmo após os 14 dias, adotados como período para equilíbrio do potencial da água do solo. Pôde-se concluir que é exatamente a existência da histerese, aliada a um umedecimento ou secagem a partir da face dos corpos de prova que não são suficientemente lentos, que resultam na não homogeneidade de umidade.

This project was a step forward in developing a reliable, economical and accurate real-time warning system for rainfall-induced individual landslides based on physical-based, optimised slope monitoring and statistical and numerical approaches. The physical-based system involved experimental and numerical analyses in implementing a low-cost slope monitoring system in critical slopes in North Maleny, evaluating parameters of tilt angle (and tilt rate), the volumetric water content of soil and rainfall. The thesis further investigated auxiliary landslide prediction approaches, including rainfall intensity–duration thresholds and analytical time to failure predictions to enhance the accuracy and reliability of outcomes.

碩士
國立中興大學
水土保持學系所
96
This study used the pressure plate experiment to obtain soil water characteristic curves in the laboratory. Thirteen soil samples includeng sand, sandy loam, loam, clayey loam, and clay used to establish the relationship of soil water content and pressure potential. The parameters α and n of the van Genuchten Model were obtained by curve fitting technique. Multiple regression equations were estimated using soil physical properties and statistical SPSS software. Three soil samples were used to validate suitability of the equations. This study also defined the range of the equation parameters for different soil texture in Taiwan. Six soil physical properties including bulk density, porosity, field capacity, percent of sand, percent of clay, organic matter content were correlated with α and n parameters of the van Genuchten model. Regression analysis results showed that the equation parameter α and n related the best with the loamy soil water characteristic curve, followed by sandy loam, and clay loam. The estimated regression equation were as follows: ln(α)=1.228BD+8.226*10-2f-5.868*10-2FC+4.86*10-2sand+2.885*10-2clay+0.233C-12.743 ln(n)=2.239BD+4.49*10-2f-1.243*10-2FC+4.254*10-3sand+9.193*10-3clay+1.397*10-2C-4.838 The range of the van Genuchten Model for parameter α is as 0.002734 cm-1 for sand；0.001695∼0.014591cm-1 for sandy loam；0.000460∼0.002804cm-1 for loam；0.000292∼0.017212cm-1 for clay loam；0.000247∼0.000447cm-1 for clay. Due to the parameter n was not significantly related to soil texture, its range, therefore, was not defined in this study.

碩士
國立臺灣科技大學
營建工程系
93
Classical soil mechanics doesn’t consider the influence of the matric suction in unsaturated soils on shear strength. However, mechanics of unsaturated soils is involved in many geotechnical problems. The objective of this study is to estimate the shear strength of unsaturated soils by using a simplified method. Base on the pressure plate test, the salt solution test and the filter paper test on Linkou Terrace Lateritic Soil, the equation of complete soil-water characteristic curve is established from the regressive analysis. At last, the shear strength of unsaturated soil estimated from the soil-water characteristic curve is used in the numerical analysis. The results indicate that a reasonable complete soil-water characteristic curve can be established from the pressure plate test and the salt solution test. Key parameters determined from the soil-water characteristic curve are Air Entry Suction(ua-uw)a=290kPa, Residual Matric Sucion(ua-uw)r=21000kPa, Saturated Volumetric Water content θs =0.54, Residual Volumetric Water content θr=0.0216. It is more reasonable to analyze the slide behavior of the unsaturated soil slope by using the shear strength estimated from soil-water characteristic curve. Compared to using the shear strength obtained from the traditional triaxial unsaturated unconfining undrained (UUU) shear strength test, it is more rigorous to apply the model proposed by this study while analyzing the stability of the unsaturated soil slope.

碩士
國立臺灣科技大學
營建工程系
98
Former studies have indicated that unstable slope locating near the watershed of a reservoir is often covered by unsaturated colluvium soils. During the dry season, high matric suction exists in the ground and maintains its stability. However, after rainfall the collapse of soil slope can occur due to infiltration and saturation of the surface soils. In order to understand the colluvium soil characteristics including both macroscopic and microscopic properties, this study adopts the colluvium soil samples nearby the Sha Lun Tsai landslide area in Shihmen reservoir. The variation of soil characteristics is investigated by samples taken from different location. A series of experiments including both field and lab tests were conducted. The soil water characteristic curve (SWCC) was used to estimate the unsaturated shear strength parameters. The slope stability analyses were, then, performed using STEDwin 2.64 program at various rainfall infiltration levels. In addition, this study also preliminary develops a set of stress-dependent SWCC equipment for future study to evaluate the effect of stress state on the SWCC. The test results exhibit that the colluvium soil samples of the same watershed mainly contain illite mineral with similar percentage of content. Moreover, the water retention capacity of the remold colluvium soil and undisturbed residual soil is better than that of the undisturbed colluvium soil. Slope stability analyses indicated that the factor of safety decreases with the increase in rainfall infiltration depth, and the potential slip surface becomes shallower when the infiltration depth increases. Therefore, it can be concluded that the “wetting-front” of rainfall infiltration is the most essential factor that can induce shallow slip failure of the colluvium soil slope.

Unsaturated soil mechanics is an important topic to deal with at the post graduate level because textbooks cover the theories related to soils in a completely dry or a completely saturated condition. Recently, it has been shown that attention must be given to soils that do not fall into these common categories. Many of these soils can be classified as unsaturated soils. As a geotechnical expert, we have to encounter soils which are in a state of partial saturation. And it becomes necessary to understand the basic behavior of these kinds of soils in order to carry out any construction activity on them. Engineering related to unsaturated soils has typically remained empirical due to the complexity of their behaviour. An unsaturated soil consists of more than two phases and therefore the natural laws governing its behaviour are changed and the principle of soil suction comes into action. So, a basic understanding about the concept of soil suction, its components, its representation, various methods with their relative advantages and limitations and a detailed description of filter paper method to measure soil suction has been presented in this report. An experimental setup has been designed which can be used in the laboratory. The procedure to obtain a calibration curve required to obtain the results has also been provided, along with the models of various researchers to obtain soil water characteristic curve and unsaturated hydraulic conductivity. The effect of compaction on these parameters has also been dealt with.

碩士
中興大學
水土保持學系所
95
The experimental system of hydraulic conductivity in the laboratory were setup, and the water characteristic curves were measured by pressure plate. Water characteristic curves and unsaturated hydraulic conductivity of different soil texture (sandy loam, clayey loam, loam) were obtained. The parameters of van Genuchten Model were obtained by curve fitting technique and then to calculate hydraulic conductivity. In order to understand whether this experiment could substitute for the pressure plate, and discusses the usable parameter of these three soils. The result shows that our experiment can obtain the best water characteristic curve in the clayey loam, next is the sandy loam, latter is the loam. The result of the unsaturated conductivity experiment shows that the most correct experiment is in the clayey loam, next is the loam, latter is the sandy loam. The parameters of the van Genuchten Model are α=0.00194, n=2.455; α=0.00168, n=2.695; α=0.00137, n=3.151 for sandy loam, loam and clayey loam respectively in this study.

碩士
國立臺北科技大學
土木與防災研究所
97
Soil water characteristic curve (SWCC) is an important function of unsaturated soil. It defines the volumetric water content corresponding to a particular suction in the soil. Experimental derivation of SWCC is time consuming and, hence, many scholars proposed simple models to back analyze SWCC. The models available are Burdine (1953), Gardner (1958), van Genuchten (1980), Fredlund and Xing (1994), etc.. In additional, there are also functions proposed to estimate SWCC from available soil properties such as particle-size distribution, bulk density, void rate and liquid limit. These estimation functions were referred to as pedo-transfer function (PTF) and some of the examples are Gupta and Larson (1975), Vereecken et al. (1989), Fredlund et al. (1997), Scheinost et al. (1997), Zhuang et al. (2001), and Aubertin (2003). In this study, we back analyzed the SWCC of some 185 soil specimens of different textures using the above four simple models and found that van Genuchten (1980)’s model performed best among the four models. The above six PTFs were also used to estimate the SWCC of the soil specimens. Of all PTFs, we find that Gupta and Larson PTF (1979) is the best PTF model to fit our sample.

碩士
立德管理學院
資源環境研究所
92
Since the entry into WTO, Taiwan faces the urgency of water usage regulation for agricultural water management. The soil water characteristic curve of the soil suction and soil water content is determined for reference to estimate agriculture water requirements for upland and paddy crops. Watermark and datalogger are installed at depth of 5cm, 10cm, 20cm, 30cm, 40cm, 60cm, and 90cm underneath the ground surface in the HsuehChai Experiment Station of ChaiNan Irrigation Association to collect soil suction data. Soil water gravimetric method, sandbox test, and pressure cooker test are applied to measure the soil water content. The results are applied to obtain the soil water characteristic curve, and RETC model is applied to obtain the parameters for the soil water characteristic curve: (1) θr =0.067; (2) θs =0.341; (3) α=0.0579; (4) n=2.4098; (5) m=0.585; the relative coefficient is 0.95. In other words, the soil water characteristic curve and its parameters for seven soil layer depth are obtained. Field tests are conducted at HsuehChai Experiment Station, and the experiment fields include: (1) regular paddy field irrigation area; (2) adjusted irrigation project area for paddy crop, and (3) upland crop area. The field tests are conduced for double paddy field in early July. Based on soil water characteristic curve, the water budget balance method and irrigation management model can applied to simulate crops water requirements in future work.

abstract: The infrastructure is built in Unsaturated Soils. However, the geotechnical practitioners insist in designing the structures based on Saturated Soil Mechanics. The design of structures based on unsaturated soil mechanics is desirable because it reduces cost and it is by far a more sustainable approach. The research community has identified the Soil-Water Characteristic Curve as the most important soil property when dealing with unsaturated conditions. This soil property is unpopular among practitioners because the laboratory testing takes an appreciable amount of time. Several authors have attempted predicting the Soil-Water Characteristic Curve; however, most of the published predictions are based on a very limited soil database. The National Resources Conservation Service has a vast database of engineering soil properties with more than 36,000 soils, which includes water content measurements at different levels of suctions. This database was used in this study to validate two existing models that based the Soil-Water Characteristic Curve prediction on statistical analysis. It was found that although the predictions are acceptable for some ranges of suctions; they did not performed that well for others. It was found that the first model validated was accurate for fine-grained soils, while the second model was best for granular soils. For these reasons, two models to estimate the Soil-Water Characteristic Curve are proposed. The first model estimates the fitting parameters of the Fredlund and Xing (1994) function separately and then, the predicted parameters are fitted to the Fredlund and Xing function for an overall estimate of the degree of saturation. Results show an overall improvement on the predicted values when compared to existing models. The second model is based on the relationship between the Soil-Water Characteristic Curve and the Pore-Size Distribution of the soils. The process allows for the prediction of the entire Soil-Water Characteristic Curve function and proved to be a better approximation than that used in the first attempt. Both models constitute important tools in the implementation of unsaturated soil mechanics into engineering practice due to the link of the prediction with simple and well known engineering soil properties.
Dissertation/Thesis
M.S. Civil and Environmental Engineering 2011

碩士
國立中興大學
水土保持學系所
101
The soil water characteristic curve is related to soil porosity distribution. However, soil porosity distribution is greatly related to soil particle-size distribution. As such, this study will focus on soil particle-size distribution and the soil water characteristic curve. By applying the Fredlund particle-size distribution model (Fredlund, 2000) and the Fredlund and Xing water content characteristic model (the FX-model) (Fredlund and Xing, 1994), the indoor experiment data will be fitted for further estimation. During the indoor experiment, the experiment process of the soil water characteristic curve is complicated and time-consuming. To save time and labor, this study intended to estimate the soil water characteristic curve by using soil particle-size distribution. For model fitting results, both the Fredlund model (Fredlund, 2000) and FX-model have a very good fit. To estimate the soil water characteristic curve, this study uses particle-size distribution to determine the parameters of αf, nf, mf and ψγ of the FX-model and then indirectly to estimate the soil water characteristic curve. This study provides three methods for determining αf and ψγ: Case 1 – to determine the corresponding matric potential of the inflection point on the soil water characteristic curve, which is equal to αf, and ψγ is the suggested value 3000(kPa) by Fredlund (1994); Case 2 – to calculate the air-entry value and the ψγ value by using the equivalent particle diameter (DH). The air-entry value is equal to the αf value; Case 3 – to determine the corresponding effective grain diameter (dea) of the air-entry value and the corresponding effective grain diameter (der) of ψγ and then to determine αf and ψγ. Then, nf and mf are estimated by using an estimation formula based on the effective grain diameter, proposed by Fredlind (2002). For estimation results, though the success rate is not high, however the results of Case 1 and Case 3 are better than Case 2, while Case 3 is slightly better than Case 1.

The current design procedure for cantilever structures on spread footings in the Texas Department of Transportation (TxDOT) is based on horizontal pressure that is calculated by using Rankine's and Coulomb's theory. These are classical Geotechnical Engineering methods. Horizontal earth pressure due to moisture and volume change in high plasticity soil is not determined by these classical methods. However, horizontal pressure on most of the cantilever retaining structures in Texas is determined by following the classical methods. In recent years, a number of consultants have considered the horizontal pressure due to swelling on cantilever retaining structures in Texas. However, the proposed horizontal pressure by consultants is 10-20 times higher than the classical horizontal pressure. This method of cantilever retaining structure design without knowing the real pressure and stress pattern increases the thickness of the wall, and raises the cost of construction. This study focuses on providing adequate patterns of lateral earth pressure distribution on cantilever retaining structures in expansive soil. These retaining wall structures are subject to swelling pressures which cause horizontal pressures that are larger than the classical especially near the ground surface. Beside the prediction of lateral earth pressure distribution, the relations between water content, volume change and suction change are determined. Based on the laboratory testing program conducted, Soil Water Characteristic Curves (SWCC) are determined for a site located at the intersection of I-35 and Walters Street in San Antonio, Texas. Additionally, relations between volume change with confining pressure curve, water content change with the change of confining pressure curve, water content change with change of matric suction and volume change with change of matric suction curves are generated based on laboratory tests. There are a number of available mass volume measurement methods that use mostly mercury or paraffin to obtain volume measurements. Although these methods are reported in the literature, they are not used in practice due to application limitations like safety, time, and cost. In order to overcome these limitations, a new method was developed to measure the volume of soil mass by using sand displacement. This new method is an inexpensive, safe, and simple way to measure mass volume by Ottawa sand.

碩士
國立臺灣科技大學
營建工程系
94
Because the water content of the in-situ soil is usually in unsaturated state which lies in between dry and fully saturated conditions. For many engineering project such as railway, highway, airport or slope engineering, compacted soils are often used. So, in the engineering analysis, it is essential to consider the influence of compaction conditions on the unsaturated soil behavior. A series of laboratory tests were conducted to determine the complete soil-water characteristic curve of the compacted lateritic soils. The engineering parameters of the compacted unsaturated soils were also evaluated by the complete soil-water characteristic curves. In addition, the influences of different Proctor energy and water content on the soil-water characteristic curve of the unsaturated compacted lateritic soils were also studied. The experimental results of show that, because the dry of optimum compacted lateritic soils exhibit massive soil structure, the initial water content is larger than that of O.M.C, wet of optimum of compacted lateritic soils and the undisturbed lateritic soils. As a result, the volumetric water content is the largest at low matric suction for the dry of optimum compacted soils. The ability of holding water is the lowest for the dry of optimum compacted soils. So, when the matric suction increases, the volumetric water content decreases significantly. As a result, its volumetric water content is lower than that of O.M.C, wet of optimum and the undisturbed soils at high matric suction. The results derived from the empirical formula and laboratory suction measurements shows that the total cohesion of lateritic soils compacted at O.M.C. is larger than that of dry of optimum and wet of optimum.

碩士
國立高雄第一科技大學
營建工程研究所
99
Soil-Water Characteristic Curve can describe the behavior of unsaturated soils by estimating their parameters. Diverse soils would have distinct elements that affect the water content such as particle size distribution, soil structure, etc. Yet, these elements would influence the different evaluation of Soil-Water Characteristic Curve for various soils. This research uses Pressure Plate Test to investigate the weathered shale taken from 7 distinctive depths. Each depth would have different levels of weathering and would produce different Soil-Water Characteristic Curve. Therefore, the research probes the effect of the particle size on the Soil-Water Characteristic Curve. The research indicates that if the slope were closer to the bottom, the particle size distribution would be finer. Therefore, according to the level of weathering, the closer to the bottom, the higher level of weathering it will be. However, weathered soil is not only soil, but has some coarse grained material in them. Moreover, the coarse grained material could directly affect the available water capacity. Hence, it appears to have lesser water content in Soil-Water Characteristic Curve. At smaller suction range, soil would be influenced by the presence of coarse grained soil. When at smaller suction value, water would start to move out of the pores. It has the similar behavior of coarse grained soil. Through the comparison of particle size distribution parameter and Soil-Water Characteristic Curve regression parameter, parameter a,m,n could be affected by initial void ratio e, effective grain size D10, and, particle size distribution. Therefore, use simple physical property as the estimate of the parameter of Soil-Water Characteristic Curve formed from weathered shale.

碩士
國立中央大學
應用地質研究所
98
Infiltration test is an important technique to investigate the hydrologic properties in soils, while the unsaturated flow numerical models can be an efficient tool to understand flow mechanism when the physical properties and conditions of soils are changed. This study employs HYDRUS-1D model and self developed Levenberg-Marquardt algorithm to inversely estimate parameters in the van Genuchten formula. The developed LM model was tested based on the synthetically generated data from HYDRUS-1D model. Additionally, the initial guesses of soil parameters in LM model were systematically analyzed to obtain general insight into the laboratory and field scale applications. The tested model was then used to estimate soil parameters of laboratory sand box under different infiltration scenarios. During the infiltration tests, the suction or pressure and water content were measured with tensiometers TDR(Time Domain Reflectometry). Such measured data can thus be used in the LM model to estimate the soil parameters. The estimated parameters were compared with those based on trial and error approach. Field scale double-ring infiltration was tested on the river bank of Zhuoshui river near His-Luo. The saturated infiltration rate(fc), initial infiltration rate (f0), and infiltration parameter by using the in Horton formula were estimated by the developed LM model. The objective of the field scale test is to obtain the saturated infiltration rate(f0) to compare with the results of laboratory experiment. Estimate Van Genuchten parameters by combining the laboratory infiltration experiment of field soil sample and saturated infiltration parameters. The results of the study reveal that the developed LM model associated with HYDRUS-1D model can accurately estimate van Genuchten soil parameters. The results of model test shows that the lower initial guess values would lead to better estimations of residual water content (θr) and α values. The saturated hydraulic conductivity (Ks) is the most sensitive parameter while the initial guess n values are relatively insignificant. The LM inversion of tests show that LM model associated with HYDRUS-1D model can estimate accurately van Genuchten for laboratory scale tests soil parameters. The field scale multiple depth double-ring infiltration tests reveals that the saturated infiltration rates(f0) of Zhuoshui river near His-Luo have one order of magnitude difference for different depths such depth difference of hydraulic conductivity (Ks) (0.0014 and 0.00015 cm/s) were also shown in laboratory scale tests. Based on the soil sample from Zhuoshui river the sand box experiment data were then used in LM model to estimate soil parameters. This simulation results showed that the value of α is from 0.01688 to 0.09289(cm-1), the value of n from 2.528 to 5.886(-), the material of the soil can be classified as sand and silt.

碩士
國立高雄第一科技大學
營建工程研究所
101
This research aims to present the effect of soil-water characteristic curve on the stability of unsaturated soil slopes by using the Finite Element Method PLAXIS 2D. This research employed similar geography of slope in same rainfall intensity, rainfall pattern, and 24 hours of rainfall duration, and then analyzed the result of the stability of unsaturated soil slopes. Proceed to examining on the effect between each data(hydrologic parameters：α value, m value, n value, saturated hydrologic conductivity Ksat and residual degree of saturation Sr) on the stability of unsaturated soil slopes. The experimental results indicated that the safety coefficient showed utmost variation on α value. α value is main controller of soil air-entry value(AEV) and soil relative permeability, which means the mount of matric suction and flow rate had a great effect upon the stability of unsaturated soil slopes. Nevertheless, most of customary analysis the stability of unsaturated soil slopes not only didn’t involve soil initial potential head, but also are based on the assumption to analyze it, hence; the assumption resulted in different condition between real condition frequently. In order to present similar slope, simulate data were set according to pore pressure head in different environments such as in the rain season, dry season, or according to thickness define hydrostatic profiles. Probing into the influence of different initial potential head on the stability of unsaturated soil slopes. In conclusions, the differentia of the stability of unsaturated soil slopes showed significant depend on initial potential head before rainfall.

博士
臺灣大學
生物環境系統工程學研究所
95
The soil volumn (or the porosity) would change with respect to natural event such as seasonal variation, precipitation, earthquake, or human activities, such as irrigation, pumping, and structure building. Two kinds of previous studies on this field:(1) the consolidation or compaction due to stress changed in the soil by natural enents or human activities, while the the water retention curve(WRC) is considered to have fixed parameters; (2) the relation between the change of porosity and hydraulic parameters of soil, because the hydraulic properties, such as the saturated hydraulic conductivity or parameters of water retention curve, of the soil must be somewhat changed due to the change in soil volume or porosity. But this kind of research barely discussed the soil water movement with respect to the change of hydraulic parameters. The purpose of this study is to find out the interactive mechanism between change of porosity, hysteresis and soil water movement. This research considers that the change of volumn or porosity in the unsaturated soil will directly influence the behavior of the water retention curve, and thus the mechanism of soil water movement. This study finds out the linear relation between the WRC parameters and the porosity of quartz sand with a WRC sand box test. Besides, a recycling water level sand box test is also conducted to study the interactive relation of water content, soil water tension and soil volumn by controlling the boundary condition to similuate the groundwater change. In the mean time, a consolidation process followed by a swelling process is found during drainage. In the infiltration simulation, while the porosity becomes smaller due to compaction, higher water content appears near the top boundary, and the wetting front depth decreases with the porosity. When top boundary flux is set to zero, the depth of the highest water content decreases with porosity. Besides, no matter the top boundary is zero flux or non-zero flux, the deepest wetting front always occurs in the soil with the highest porosity. In addition, the result of the recycling water level sand box test is verified with a hysteresis model. The results show that the repeated water level change will lead to the change of property of water retention curve and soil consolidation, indicating that the change of water content and soil water tension is caused by hysteresis, as well as change of porosity.

Deep geological repository (DGR) for disposal of high-level radioactive waste (HLW) is designed to rely on successive superimposed barrier systems to isolate the waste from the biosphere. This multiple barrier system comprises the natural geological barrier provided by the repository host rock and its surrounding and an engineered barrier system (EBS). The EBS represents the synthetic, engineered materials placed within the natural barrier, comprising array of components such as waste form, waste canisters, buffer materials, backfill and seals. The buffer will enclose the waste canisters from all directions and act as a barrier between canisters and host rock of the repository. It is designed to stabilise the evolving thermo-hydro-mechanical-chemical stresses in the repository over a long period (nearly 1000 years) to retard radionuclides from reaching biosphere. Bentonite clay or bentonite-sand mix have been chosen as buffer materials in EBS design in various countries pursuing deep geological repository method. The bentonite buffer is the most important barrier among the other EBS components for a geological repository. The safety of repository depends to a large extent on proper functioning of buffer over a very long period of time during which it must remain physically, chemically and mineralogically stable. The long term stability of bentonite buffer depends on varying temperature and evolution of groundwater composition of host rocks in a complex way. The groundwater in the vicinity of deep crystalline rock is often characterized by high solute concentrations and the geotechnical engineering response of bentonite buffer could be affected by the dissolved salt concentration of the inflowing ground water. Also during the initial period, radiogenic heat produced in waste canisters would radiate into buffer and the heat generated would lead to drying and some shrinkage of bentonite buffer close to canister. This could alter the dry density, moisture content and in turn the hydro-mechanical properties of bentonite buffer in DGR conditions. India has variety of bentonite deposits in North-Western states of Rajasthan and Gujarat. Previous studies on Indian bentonites suggest that bentonite from Barmer district of Rajasthan (termed as Barmer-1 bentonite) is suitable to serve as buffer material in DGR conditions. Nuclear power agencies of several countries have identified suitable bentonites for use as buffer in DGR through laboratory experiments and large scale underground testing facilities. Physico-chemical, mineralogical and engineering properties of Kunigel VI, Kyungju, GMZ, FoCa clay, MX-80, FEBEX and Avonseal bentonites have been extensively studied by Japan, South Korea, China, Belgium, Sweden, Spain, Canada. It is hence essential to examine the suitability of Barmer-1 bentonite as potential buffer in DGR and compare its physico-chemical and hydromechanical properties with bentonite buffers identified by other countries. The significant factors that impact the long-term stability of bentonite buffer in DGR include variations in moisture content, dry density and pore water chemistry. With a view to address these issues, the hydromechanical response of 70 % Barmer-1 bentonite + 30 % river sand mix (termed bentonite enhanced sand, BES specimens) under varying moisture content, dry density and pore water salt concentration conditions have been examined. The broad scope of the work includes: 1) Characterise the physico-chemical and hydro-mechanical properties of Barmer-1 bentonite from Rajasthan, India and compare its properties with bentonite buffers reported in literature. 2) Examine the influence of variations in dissolved salt concentration (of infiltrating solution), dry density and moisture content of compacted BES specimens on their hydro-mechanical response; the hydro-mechanical properties include, swell pressure, soil water characteristic curve (SWCC), unsaturated hydraulic conductivity, moisture diffusivity and unconfined compression strength. Organization of thesis: After the first introductory chapter, a detailed review of literature is performed to highlight the need for detailed characterisation of physico-chemical and hydromechanical properties of Barmer-1 bentonite for its possible application in DGR in the Indian context. Further, existing literature on hydro-mechanical response of bentonite buffer to changes in physical (degree of saturation/moisture content, dry density) and physico-chemical (solute concentration in pore water) is reviewed to define the scope and objectives of the present thesis in Chapter 2. Chapter 3 presents a detailed experimental programme of the study. Chapter 4 characterises Barmer-1 bentonite for physico-chemical (cation exchange capacity, pore water salinity, exchangeable sodium percentage) and hydro-mechanical properties, such as, swell pressure, saturated permeability, soil water characteristic curve (SWCC) and unconfined compression strength. The properties of Barmer-1 bentonite are compared with bentonite buffers reported in literature and generalized equations for determining swell pressure and saturated permeability coefficient of bentonite buffers are arrived at. Chapter 5 describes a method to determine solute concentrations in the inter-lamellar and free-solutions of compacted BES (bentonite enhanced sand) specimens. The solute concentrations in micro and macro pore solutions are used to examine the role of osmotic flow on swell pressures developed by compacted BES specimens (dry density 1.50-2.00 Mg/m3) inundated with distilled water and NaCl solutions (1000-5000 mg/L). The number of hydration layers developed by the compacted BES specimens on inundation with salt solutions in constant volume swell pressure tests is controlled by cation hydration/osmotic flow. The cation hydration of specimens compacted to dry density of 2.00 Mg/m3 is mainly driven by matric suction prevailing in the clay microtructure as the number of hydration layers developed at wetting equilibrium are independent of the total dissolved solids (TDS) of the wetting solution. Consequently, the swell pressures of specimens compacted to 2.00 Mg/m3 were insensitive to the salt concentration of the inundating solution. The cation hydration of specimens compacted to dry density of 1.50 Mg/m3 is driven by both matric suction (prevailing in the clay micro-structure) and osmotic flow as the number of hydration layers developed at wetting equilibrium is sensitive to the TDS of the wetting solution. Expectedly, the swell pressures of specimens compacted to 1.50 Mg/m3 responded to changes in salt concentration of the inundating solution. The 1.75 Mg/m3 specimens show behaviour that is intermediate to the 1.50 and 2.00 Mg/m3 series specimens. Chapter 6 examines the influence of initial degree of saturation on swell pressures developed by the compacted BES specimens (dry density range: 1.40- 2.00 Mg/m3) on wetting with distilled water from micro-structural considerations. The micro-structure of the bentonite specimens are examined in the compacted and wetted states by performing X-ray diffraction measurements. The initial degree of saturation is varied by adding requisite amount of distilled water to the oven-dried BES mix and compacting the moist mixes to the desired density. The montmorillonite fraction in the BES specimens is responsible for moisture absorption during compaction and development of swell pressure in the constant volume oedometer tests. Consequently, it was considered reasonable to calculate degree of saturation based on EMDD (effective montmorillonite dry density) values and correlate the developed swell pressure values with degree of saturation of montmorillonite voids (Sr,MF). XRD measurements with compacted and wetted specimens demonstrated that if specimens of density series developed similar number of hydration layers on wetting under constant volume condition they exhibited similar swell pressures, as was the case for specimens belonging to 1.40 and 1.50 Mg/m3 series. With specimens belonging to 1.75 and 2.00 Mg/m3 series, greater number of hydration layers were developed by specimens that were less saturated initially (smaller initial Sr,MF) and consequently such specimens developed larger swell pressures. When specimens developed similar number of hydration layers in the wetted state, the compaction dry density determined the swell pressure. Chapter 7 examines the influence of salt concentration of infiltrating solution (sodium chloride concentration ranges from 1000- 5000 mg/L) on SWCC relations, unsaturated permeability and moisture diffusivity of compacted BES specimens. Analysis of the experimental and Brooks and Corey best fit plots revealed that infiltration of sodium chloride solutions had progressively lesser influence on the micro-structure and consequently on the SWCC relations with increase in dry density of the compacted specimens. The micro-structure and SWCC relations of specimens compacted to 1.50 Mg/m3 were most affected, specimens compacted to 1.75 Mg/m3 were less affected, while specimens compacted to 2.00 Mg/m3 were unaffected by infiltration of sodium chloride solutions. Variations in dry density of compacted bentonite impacts the pore space available for moisture flow, while, salinity of wetting fluid impacts the pore structure from associated physico-chemical changes in clay structure. Experimental results showed that the unsaturated permeability coefficient is insensitive to variations in dry density and solute concentration of wetting liquid, while, the effective hydraulic diffusivity is impacted by variations in these parameters. Chapter 8 summarises the major findings of the study.

Deep geological repository (DGR) for disposal of high-level radioactive waste (HLW) is designed to rely on successive superimposed barrier systems to isolate the waste from the biosphere. This multiple barrier system comprises the natural geological barrier provided by the repository host rock and its surrounding and an engineered barrier system (EBS). The EBS represents the synthetic, engineered materials placed within the natural barrier, comprising array of components such as waste form, waste canisters, buffer materials, backfill and seals. The buffer will enclose the waste canisters from all directions and act as a barrier between canisters and host rock of the repository. It is designed to stabilise the evolving thermo-hydro-mechanical-chemical stresses in the repository over a long period (nearly 1000 years) to retard radionuclides from reaching biosphere. Bentonite clay or bentonite-sand mix have been chosen as buffer materials in EBS design in various countries pursuing deep geological repository method. The bentonite buffer is the most important barrier among the other EBS components for a geological repository. The safety of repository depends to a large extent on proper functioning of buffer over a very long period of time during which it must remain physically, chemically and mineralogically stable. The long term stability of bentonite buffer depends on varying temperature and evolution of groundwater composition of host rocks in a complex way. The groundwater in the vicinity of deep crystalline rock is often characterized by high solute concentrations and the geotechnical engineering response of bentonite buffer could be affected by the dissolved salt concentration of the inflowing ground water. Also during the initial period, radiogenic heat produced in waste canisters would radiate into buffer and the heat generated would lead to drying and some shrinkage of bentonite buffer close to canister. This could alter the dry density, moisture content and in turn the hydro-mechanical properties of bentonite buffer in DGR conditions. India has variety of bentonite deposits in North-Western states of Rajasthan and Gujarat. Previous studies on Indian bentonites suggest that bentonite from Barmer district of Rajasthan (termed as Barmer-1 bentonite) is suitable to serve as buffer material in DGR conditions. Nuclear power agencies of several countries have identified suitable bentonites for use as buffer in DGR through laboratory experiments and large scale underground testing facilities. Physico-chemical, mineralogical and engineering properties of Kunigel VI, Kyungju, GMZ, FoCa clay, MX-80, FEBEX and Avonseal bentonites have been extensively studied by Japan, South Korea, China, Belgium, Sweden, Spain, Canada. It is hence essential to examine the suitability of Barmer-1 bentonite as potential buffer in DGR and compare its physico-chemical and hydromechanical properties with bentonite buffers identified by other countries. The significant factors that impact the long-term stability of bentonite buffer in DGR include variations in moisture content, dry density and pore water chemistry. With a view to address these issues, the hydromechanical response of 70 % Barmer-1 bentonite + 30 % river sand mix (termed bentonite enhanced sand, BES specimens) under varying moisture content, dry density and pore water salt concentration conditions have been examined. The broad scope of the work includes: 1) Characterise the physico-chemical and hydro-mechanical properties of Barmer-1 bentonite from Rajasthan, India and compare its properties with bentonite buffers reported in literature. 2) Examine the influence of variations in dissolved salt concentration (of infiltrating solution), dry density and moisture content of compacted BES specimens on their hydro-mechanical response; the hydro-mechanical properties include, swell pressure, soil water characteristic curve (SWCC), unsaturated hydraulic conductivity, moisture diffusivity and unconfined compression strength. Organization of thesis: After the first introductory chapter, a detailed review of literature is performed to highlight the need for detailed characterisation of physico-chemical and hydromechanical properties of Barmer-1 bentonite for its possible application in DGR in the Indian context. Further, existing literature on hydro-mechanical response of bentonite buffer to changes in physical (degree of saturation/moisture content, dry density) and physico-chemical (solute concentration in pore water) is reviewed to define the scope and objectives of the present thesis in Chapter 2. Chapter 3 presents a detailed experimental programme of the study. Chapter 4 characterises Barmer-1 bentonite for physico-chemical (cation exchange capacity, pore water salinity, exchangeable sodium percentage) and hydro-mechanical properties, such as, swell pressure, saturated permeability, soil water characteristic curve (SWCC) and unconfined compression strength. The properties of Barmer-1 bentonite are compared with bentonite buffers reported in literature and generalized equations for determining swell pressure and saturated permeability coefficient of bentonite buffers are arrived at. Chapter 5 describes a method to determine solute concentrations in the inter-lamellar and free-solutions of compacted BES (bentonite enhanced sand) specimens. The solute concentrations in micro and macro pore solutions are used to examine the role of osmotic flow on swell pressures developed by compacted BES specimens (dry density 1.50-2.00 Mg/m3) inundated with distilled water and NaCl solutions (1000-5000 mg/L). The number of hydration layers developed by the compacted BES specimens on inundation with salt solutions in constant volume swell pressure tests is controlled by cation hydration/osmotic flow. The cation hydration of specimens compacted to dry density of 2.00 Mg/m3 is mainly driven by matric suction prevailing in the clay microtructure as the number of hydration layers developed at wetting equilibrium are independent of the total dissolved solids (TDS) of the wetting solution. Consequently, the swell pressures of specimens compacted to 2.00 Mg/m3 were insensitive to the salt concentration of the inundating solution. The cation hydration of specimens compacted to dry density of 1.50 Mg/m3 is driven by both matric suction (prevailing in the clay micro-structure) and osmotic flow as the number of hydration layers developed at wetting equilibrium is sensitive to the TDS of the wetting solution. Expectedly, the swell pressures of specimens compacted to 1.50 Mg/m3 responded to changes in salt concentration of the inundating solution. The 1.75 Mg/m3 specimens show behaviour that is intermediate to the 1.50 and 2.00 Mg/m3 series specimens. Chapter 6 examines the influence of initial degree of saturation on swell pressures developed by the compacted BES specimens (dry density range: 1.40- 2.00 Mg/m3) on wetting with distilled water from micro-structural considerations. The micro-structure of the bentonite specimens are examined in the compacted and wetted states by performing X-ray diffraction measurements. The initial degree of saturation is varied by adding requisite amount of distilled water to the oven-dried BES mix and compacting the moist mixes to the desired density. The montmorillonite fraction in the BES specimens is responsible for moisture absorption during compaction and development of swell pressure in the constant volume oedometer tests. Consequently, it was considered reasonable to calculate degree of saturation based on EMDD (effective montmorillonite dry density) values and correlate the developed swell pressure values with degree of saturation of montmorillonite voids (Sr,MF). XRD measurements with compacted and wetted specimens demonstrated that if specimens of density series developed similar number of hydration layers on wetting under constant volume condition they exhibited similar swell pressures, as was the case for specimens belonging to 1.40 and 1.50 Mg/m3 series. With specimens belonging to 1.75 and 2.00 Mg/m3 series, greater number of hydration layers were developed by specimens that were less saturated initially (smaller initial Sr,MF) and consequently such specimens developed larger swell pressures. When specimens developed similar number of hydration layers in the wetted state, the compaction dry density determined the swell pressure. Chapter 7 examines the influence of salt concentration of infiltrating solution (sodium chloride concentration ranges from 1000- 5000 mg/L) on SWCC relations, unsaturated permeability and moisture diffusivity of compacted BES specimens. Analysis of the experimental and Brooks and Corey best fit plots revealed that infiltration of sodium chloride solutions had progressively lesser influence on the micro-structure and consequently on the SWCC relations with increase in dry density of the compacted specimens. The micro-structure and SWCC relations of specimens compacted to 1.50 Mg/m3 were most affected, specimens compacted to 1.75 Mg/m3 were less affected, while specimens compacted to 2.00 Mg/m3 were unaffected by infiltration of sodium chloride solutions. Variations in dry density of compacted bentonite impacts the pore space available for moisture flow, while, salinity of wetting fluid impacts the pore structure from associated physico-chemical changes in clay structure. Experimental results showed that the unsaturated permeability coefficient is insensitive to variations in dry density and solute concentration of wetting liquid, while, the effective hydraulic diffusivity is impacted by variations in these parameters. Chapter 8 summarises the major findings of the study.