Download or read book Determination of Diffusion Coefficient Through Laboratory Tests and Analytically Validating it Using Empirical Relations for Unsaturated Soils written by Anshuman B. Thakur and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Soil suction is one of the most important physical variables affecting the soil engineering behavior, moisture content. Suction has a major controlling influence on soil shear strength. The moisture diffusivity properties of unsaturated properties of soils exert a critical influence on the depth to which seasonal variations of moisture and suction at the ground surface extend into the soil mass. Hence, a study of moisture diffusion coefficient is pivotal. In this research the drying test originally proposed by Mitchell (1979) has been validated by back calculating the moisture diffusion values using the empirical relation established by Lytton (2003). The non-linear flow through unsaturated soils has been simplified to a linear problem for simplicity in this study. Owing to this simplification, certain refinements have therefore been applied in the determination of diffusion coefficient. Thermocouple psychrometer was used to measure the soil suction along the length of the sample and at different times in the laboratory. Initial suction measurements were done using the filter paper test. Curve fitting procedure established by (Aubeny and Lytton, 2003), has been used for the determination of the diffusion coefficient. Analytical validation of the moisture diffusion coefficient, required coefficient of permeability, 'k', slope of suction water characteristic curve 'S' and air entry value 'h0' as the major input parameters. Mitchell (1979) assumed the value of 'h0' to be 100 cm. In this research air entry value, 'h0' has been re-evaluated and it comes out to be higher than the pre estimated value. The value of slope of suction water characteristic curve, 'S' obtained from pressure plate tests, compares well to the empirical equation of Lytton (2003). The results of moisture diffusion coefficient obtained from the empirical equation come out in the same range as obtained from the refined Mitchell's (1979) drying test. The refinements includes introduction of constant temperature environment. Owing to the least variation in temperature, more reliable and reproducible data was obtained. The range of moisture diffusion coefficient, [alpha]-values obtained from empirical equation, comes out to be coherent with the laboratory data. Hence, it can be concluded that the research was successful.
Download or read book Unsaturated Soils written by Gerald A. Miller and published by . This book was released on 2006 with total page 1328 pages. Available in PDF, EPUB and Kindle. Book excerpt: GSP 147 contains 219 papers on unsaturated soil problems presented at the Fourth International Conference on Unsaturated Soils, held in Carefree, Arizona, April 2-6, 2006.
Download or read book Determination of Diffusion Coefficient for Unsaturated Soils written by Eeshani Sood and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The structures constructed on unsaturated soils are damaged by the movement of the soil underneath. The movement is basically due to the flow of moisture in and out of the soil. This change in moisture also affects the strength of the soil, thus resulting in failure of slopes of embankments constructed with these soils. Therefore, it is very important to study the diffusion properties of unsaturated soils. Study of the diffusion properties requires the determination of the diffusion coefficient ([alpha]). In this thesis improvements in the drying test, originally proposed by Mitchell(1979), have been discussed. The study also involves defining the evaporation coefficient(h[subscript]e) which has been ill-defined in previous research work. The flow through unsaturated soils is non-linear but due to the complexity involved it has been simplified to a linear problem. The nonlinear behavior has been studied during this research. Therefore, certain refinements have been applied in the determination of the diffusion coefficient. The laboratory procedure followed involves measuring the soil suction along the length of the sample and at different times using thermocouple psychrometers. The evaluation of the evaporation coefficient (h[subscript]e) has been made an integral part of the procedure. The diffusion coefficient is determined using the curve fitting procedure of Aubeny and Lytton, 2003.
Download or read book Master s Theses Directories written by and published by . This book was released on 2006 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Education, arts and social sciences, natural and technical sciences in the United States and Canada".
Download or read book Energy Research Abstracts written by and published by . This book was released on 1994-08 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Development of a diffusion cell for unsaturated soils written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nos projetos de locais de disposição de resíduos e na avaliação da contaminação do solo e da água subterrânea por substâncias químicas orgânicas e inorgânicas, é essencial que se conheça os mecanismos de transporte de contaminantes por estes meios. São dois os processos básicos no transporte de solutos: advecção e dispersão hidrodinâmica. Advecção é o processo através do qual a água subterrânea carrega consigo os solutos dissolvidos. A quantidade de soluto transportado depende de sua concentração na águasubterrânea, do volume de água fluindo e da velocidade da água subterrânea. O mecanismo de dispersão hidrodinâmica engloba o mecanismo de dispersão mecânica e o transporte pordifusão. A medida que o soluto se movimenta no meio poroso, o processo de dispersão age no sentido de diluir o soluto e reduzir sua concentração. A difusão é o processo através do qual as espécies moleculares e iônicas dissolvidas na água se movem devido a um gradiente de concentração, indo das áreas de maior para menor concentração, mesmo na ausência de fluxo de água subterrânea. O transporte difusivo através de um meio não saturado é mais complicado do que através demeios saturados. Neste caso os parâmetros de transporte podem variar no espaço e no tempo. Portanto, a determinação destes parâmetros no laboratório deve ser feito nas condições mais próximas possíveis das condições in situ. Os processos através dos quais as substâncias se movem através do solo podem ser expressos por modelos matemáticos. Eles se baseiam na integração da equação advectiva-dispersiva utilizando condições de contorno específicas para o sistema de interesse. Entretanto, suaaplicabilidade é limitada devido à falta de parâmetros experimentais confiáveis. Esta tese procura preencher o espaço entre os modelos numéricos e os estudos experimentais. Um novo difusímetro foi desenvolvido para medir o coeficiente de difusão em solos não saturados. O projeto combina o método do reservatório simple, proposto por Rowe et al. (1988), com a técnica de controle osmótico. Foram feitos ensaios com sucção variando entre 0 e 500 kPa. Os solutos utilizados foram cloreto de sódio e cloreto de potássio difundindo através de um amostra relativamente inerte, preparada em laboratório. Os resultados obtidosindicam que a nova técnica proposta funciona bem, sendo entretanto recomendado maiores desenvolvimentos no sistema de controle de sucção, através do uso de instrumentação maisprecisa.
Download or read book A New Technique for Diffusion Testing of Unsaturated Soil written by SL. Barbour and published by . This book was released on 1996 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: A technique is proposed for determining the coefficients of diffusion and adsorption for ions in unsaturated soils. The method integrates the single reservoir diffusion testing of saturated soil with the axis-translation technique for the control of matric suction. The procedure allows for the application of a net total stress and matric suction to the soil during the diffusion test. The use of this new technique to determine the coefficients of diffusion and adsorption of ions from a single test is demonstrated. The effects of the degree of saturation on the coefficients of diffusion and adsorption were evaluated on a sandy soil with water contents ranging from saturation to near the residual degree of saturation. Potassium and chloride ions were used as the primary tracers.
Download or read book Unsaturated Soil Moisture Drying and Wetting Diffusion Coefficient Measurements in the Laboratory written by Daniel Mabirizi and published by . This book was released on 2009 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Measurement and Modeling of Solute Diffusion Coefficients in Unsaturated Soils written by Hsin-Yi Chou and published by . This book was released on 2010 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although solute diffusion in soil has been widely examined under the influence of both soil-water content and matric potential, little information is available about the impact of soil-water content/matric potential hysteresis on solute diffusion. Our research shows that the unequal soil-water content at a given matric potential when a soil is subjected to drying or wetting process has substantial impact on solute diffusion. The measured solute diffusion coefficients of drying were greater than those of wetting in certain soil-water content range. When fitted the solute diffusion coefficients of drying and wetting limbs by proposed predictive models, the drying limb is better described by a power function of soil-water content with empirical constants estimated by particle-size distribution and bulk density; while the wetting limb is better described by a conceptual model which assumes the solute diffusive pathway is comprised of the serial arrangement of pore water and film water. This research concluded that the behavior of solute diffusion in unsaturated soils is essentially determined by the liquid phase distribution.
Download or read book Agronomy Abstracts written by and published by . This book was released on 1987 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt: Includes abstracts of the annual meetings of the American Society of Agronomy; Soil Science Society of America; Crop Science Society of America ( - of its Agronomic Education Division).
Download or read book Evaluate Unsaturated Soil Behavior Using Constant Water Content Triaxial Tests written by 李林 and published by . This book was released on 2015 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: The triaxial test has been extensively used to evaluate both saturated and unsaturated soil behaviors. The conventional triaxial test apparatus for saturated soils cannot be used to test unsaturated soils due to difficulties in soil volume and suction measurement. In 1961, a suction-controlled triaxial test apparatus was developed to investigate behavior of unsaturated soils. Since this development, the suction-controlled test has been widely used for unsaturated soil characterization. Most important concepts concerning unsaturated soil mechanics were developed based upon results from suction-controlled tests. However, the suction-controlled triaxial test on unsaturated soils, which is a drained test, is usually laborious, time-consuming, and costly, and may not be justifiable for routine engineering projects. The constant water content (undrained) test has been widely used to investigate saturated soil behaviors. However, for unsaturated soils, due to difficulties in direct, rapid, and reliable suction measurement, the constant water content test was rarely used for unsaturated soil behavior evaluation. In addition, accurate volume change measurement of unsaturated soils was a great challenge for researchers. Recently, the Modified State Surface Approach (MSSA) has been developed to calibrate unsaturated soil behaviors. According to MSSA, both results from suction-controlled and constant water content triaxial tests can be used for constitutive behavior calibration on unsaturated soils. In this study, a new triaxial test system was developed to investigate unsaturated soil behaviors through constant water content triaxial tests. To measure soil suction variation during testing, a new type of high-suction tensiometer was developed based on a commercial miniature pressure transducer. A 15 bar air-entry ceramic disc was used as the filter of the high-suction tensiometer. After saturation and calibration, this new type of high-suction tensiometer could be utilized for matric suction measurement on unsaturated soils with a maximum measurable suction up to 1100 kPa determined via a free evaporation test. To measure the volume change of unsaturated soils during triaxial testing, a photogrammetry-based method was developed by integrating photogrammetry, optical-ray tracing, and least-square estimation techniques. Through two validation tests on a stainless steel cylinder and a saturated sand specimen, the average point and total volume change measurement accuracy were determined to be approximately 0.065 mm and 0.05%, respectively. With this method, the conventional triaxial test apparatus for saturated soils can be used for triaxial testing on unsaturated soils without any modification. In addition to total volume change measurement, the newly developed photogrammetry-based method can also be used to investigate the deformation characteristics of soils during triaxial testing such as full-field deformation, volumetric strain non-uniformity, full-field strain distribution, and shear band evolution process. To evaluate the performance of the new triaxial testing system, a series of constant water content triaxial tests were carried out on unsaturated soils. New methods were proposed to characterize shear strength of the tested unsaturated soils. Also, an example was given to calibrate the constitutive behavior of an unsaturated soil based on results from the constant water content triaxial tests. Analysis results indicated that the proposed triaxial testing system is a cost effective and time efficient alternative to the suction-controlled triaxial testing system. In geotechnical and highway engineering, many projects involve unsaturated soils at shallow depths with low confining stresses (less than 100 kPa). To investigate the behavior of unsaturated soils at low confining stresses, the new triaxial testing system was simplified to a modified unconfined compression testing system. In this simplified system, negative air pressure (i.e., vacuum pressure) was used to provide the low confining stress for the triaxial tests. The high-suction tensiometers were used to monitor soil matrix suction variation during testing. A photogrammetric method was utilized for deformation measurements of unsaturated soils during triaxial testing. A series of undrained triaxial tests was also carried out to demonstrate the use of the modified unconfined compression testing system for unsaturated soil behavior evaluation under different confining stresses.
Download or read book The Measurement of the Diffusion Rates of Volatile Organic Compounds Through Laboratory prepared and Intact Soils written by Paul Milne and published by . This book was released on 1996 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Diffusive and Advective diffusive Transport Through Saturated and Unsaturated Soils written by Kazem Badv and published by . This book was released on 1994 with total page 1044 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Conceptual Models of Flow and Transport in the Fractured Vadose Zone written by National Research Council and published by National Academies Press. This book was released on 2001-05-21 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fluid flow and solute transport within the vadose zone, the unsaturated zone between the land surface and the water table, can be the cause of expanded plumes arising from localized contaminant sources. An understanding of vadose zone processes is, therefore, an essential prerequisite for cost-effective contaminant remediation efforts. In addition, because such features are potential avenues for rapid transport of chemicals from contamination sources to the water table, the presence of fractures and other channel-like openings in the vadose zone poses a particularly significant problem, Conceptual Models of Flow and Transport in the Fractured Vadose Zone is based on the work of a panel established under the auspices of the U.S. National Committee for Rock Mechanics. It emphasizes the importance of conceptual models and goes on to review the conceptual model development, testing, and refinement processes. The book examines fluid flow and transport mechanisms, noting the difficulty of modeling solute transport, and identifies geochemical and environmental tracer data as important components of the modeling process. Finally, the book recommends several areas for continued research.
Download or read book Laboratory Tests for Unsaturated Soils written by E. C. Leong and published by CRC Press. This book was released on 2022-12 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the first book to systematically collate the various laboratory tests for unsaturated soils. It covers general background and theory along with test procedures and the interpretation of test results. It serves for students and researchers who are new to the field as well as for established professionals.
Download or read book Diffusion in Natural Porous Media written by Peter Grathwohl and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: Diffusion in Natural Porous Media: Contaminant Transport, Sorption/Desorption and Dissolution Kinetics introduces the general principles of diffusion in the subsurface environment and discusses the implications for the fate and transport of contaminants in soils and groundwater. Emphasis is placed on sorption/desorption and the dissolution kinetics of organic contaminants, both of which are limited by the slow speed of molecular diffusion. Diffusion in Natural Porous Media: Contaminant Transport, Sorption/Desorption and Dissolution Kinetics compiles methods for calculating the diffusion coefficients of organic compounds (in aqueous solution or vapor phase) in natural porous media. The author uses analytical solutions of Fick's 2nd law and some simple numerical models to model diffusive transport under various initial and boundary conditions. A number of these models may be solved using spreadsheets. The book examines sorption/desorption rates of organic compounds in various soils and aquifer materials, and also examines the dissolution kinetics of nonaqueous phase liquids in aquifers, in both the trapped residual phase and in pools. Diffusion in Natural Porous Media: Contaminant Transport, Sorption/Desorption and Dissolution Kinetics concludes with a discussion of the impact of slow diffusion processes on soil and groundwater decontamination and the implications of these processes for groundwater risk assessment.
Download or read book Experimental Determination of Diffusion Coefficients of Soils written by Dipak Jayantilal Shah and published by . This book was released on 1981 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:
