No description available.

No description available.

Two-dimensional analysis of four types of water-filled tube dams is carried out: an apron-tube dam, a single baffle tube dam, a sleeved tube dam, and a stacked tube dam. Since the analysis of the water-filled tube dam involves highly nonlinear geometric deformations and interactions with soil, fluid, and structure, it is solved numerically with the explicit finite difference program FLAC. The tube is numerically modeled with beam elements. The predicted contact regions are modeled with interface elements. The Mohr-Coulomb constitutive model is used for the soil. Water inside and outside of the tube is modeled as hydrostatic pressure and the pressures are continuously updated as the configuration of the tube is changed. The change of the internal water pressure head (IWPH) for maintaining a constant tube area during the deformation is simulated. The simulation is achieved by two iterative procedures, the secant method and the factored secant method. The numerical analysis results show good agreement with the experimental results overall: the deformation of the tube(s), the IWPH changes, and the critical external water heights. From the numerical simulation of the experiments and the parametric studies, the behavior of each type of water-filled tube dam is clarified. Also, the failure modes of the tube dams are examined. The failure mode of a tube dam depends on the configuration and IWPH of the tube dam and the characteristics of the soil surface. / Ph. D.

The 1999 Kocaeli Earthquake (M=7.4) struck northwestern Turkey on August 17, 1999 and caused significant damage in urban areas located along Izmit Bay. The sites that suffered the greatest damages were located primarily in areas of poorest soil conditions, typically containing soft clays and silts and/or loose, liquefiable sands. Because the affected region is heavily developed with infrastructure and there is a preponderance of poor soils, a wide range of soil improvement measures had been used to mitigate anticipated earthquake damages throughout the region. Following the earthquake and significant aftershocks, Virginia Tech researchers traveled to Turkey to investigate the affected area to document geotechnical field performance. Primary focus of the Virginia tech team was given to investigating the performance of improved soil sites and reinforced soil structures. The sites were subjected to ground motions ranging from about 0.10g to 0.35g. The site locations ranged from 0 to 35 km from the zone of energy release. This dissertation presents in detail, the findings from the two most instructive sites. The investigation of these sties involved field reconnaissance, field and laboratory testing of soils, seismic analysis, numerical modeling, and other analytical work. / Ph. D.

A formulation for modeling soil-structure interaction has been presented. In conjunction with the formulation, a computer code was written to implement it. Several problems were analyzed to demonstrate the accuracy of the code. The program called SEQCON utilizes an eight-node isoparametric quadrilateral. An interface and tar element are also available. Four material models are used. They are the linear elastic, the hyperbolic, the trucker-Prager, and the cap model. Several construction sequence steps were modeled. They include in situ, dewatering, excavation, deposition (embankment) and tie-backs. The code itself is modular in design and quite flexible. It is easy to implement and to modify. / M.S.

A finite element procedure is developed for stress-deformation analysis of three-dimensional solid bodies including geometric and material nonlinearities. The formulation also includes the soil-structure interaction effect by using an interface element. A scheme is formulated to allow consistent definitions of stress, stress and strain rates, and constitutive laws. The analysis adopts the original Newton-Raphson technique coupled with incremental approach. Different elasto-plastic laws based on Von-Mises, Drucker-Prager, critical state, and cap criteria are incorporated in the formulation and computer code, and they can be used depending on the geological material involved. A special cap model is also incorporated to predict the behavior of the artificial soil used in current research. Examples are given to verify the formulation and the finite element code. Examples of the problems of soil-moving tool are also shown to compare to the experimental solutions observed in a prototype soilbin test facility. / Ph. D.

The genetic and morphological characteristics of Hagerstown silt loam, Pisgah silt loam and Clarksville cherty silt loam, three southwest Virginia soils which were formed from material weathered from limestone, were studied by means of mechanical and chemical analyses, and field studies or the soil profiles. The soils used in this investigation are all related in a general way, that is, they all occur within the Gray-Brown Podzolic region and are all derivatives of relatively highly carbonated rocks. Samples of all three soils were taken in Russell County, Virginia within the same vicinity. Therefore, the variation in the physical and chemical composition are due to variation in parent rock and relief and not to variations in climate. Chemical analyses of the parent rock showed that the Hagerstown silt loam and Clarksville cherty silt loan were formed from material weathered from a dolomitic limestone, and that the Pisgah silt loan was formed from material weathered from a high grade limestone. Total chemical analyses of the various horizons of the soil profiles showed that the soil forming processes of the three soils studied were podzolic is nature. The parent materials or C horizons of all the soil profiles studied were clays. Hagerstown, which contained approximately 38 percent clay in the A₁ horizon and 75 percent clay in the C horizon, was the heaviest of the three soils studied. Laboratory and field classifications of soil class conflicted in the case of the Hagerstown profile. The ratios of silica to alumina, and silica to iron showed clearly the accumulation of alumina or iron in the lower horizons. The base to alumina ratio showed the thoroughness of the weathering of the three soil profiles. Calculations of the percentages of bases lost during the soil forming processes showed that calcium was lost from the soil to a greater extent than the magnesium. / Master of Science

Earth's near-surface environment sustains nearly all terrestrial life, yet this critical zone is threatened by the environmental migration of new and potentially harmful compounds produced to support a growing human population. Traditional transport equations often fail to capture the environmental behavior of these emerging contaminants due to issues such as flow heterogeneity. Thus, there is a need to better evaluate controls on pollutant partitioning in Earth's critical zone. Our first study investigated the transport and distribution of the neonicotinoid insecticide thiamethoxam (TMX) by growing TMX-coated corn seeds in coarse vs fine-textured soil columns maintained with versus without growing corn plants. Fine-textured soil transported TMX at concentrations that were two orders of magnitude higher than coarse-textured soil, due to preferential flow in the fine-textured soil columns and higher evapotranspiration (ET) concentrating more TMX in the coarse-textured soil. Living plants increased the concentration of TMX at depth, indicating that growing plants may drive preferential transport of neonicotinoids. For the second study we planted TMX-coated corn seeds and maintained field plots with and without viable crops (n = 3 plots per treatment), measuring TMX concentrations in three hydrological compartments (surface runoff, shallow lateral flow, and deep drainage) and soil. TMX was transported in the highest concentrations via surface runoff, while also showing continual migration within the subsurface throughout the growing season. Plants facilitated downward migration of TMX in soil yet restricted losses in drainage. For our final study, we used a simple isotope mixing method to evaluate how preferential flow alters the influence of compound chemical properties on solute transport. We applied deuterium-labeled rainfall to plots containing manure spiked with eight veterinary antibiotics with a range of mobility, and quantified transport to suction lysimeters (30 and 90 cm). We showed that low preferential flow (<20%) eliminates the influence of compound chemical properties and, contrary to conventional understanding, more preferential flow (~ >20%) amplifies these chemical controls, with more mobile compounds appearing in significantly higher concentrations than less mobiles ones. Altogether, we provide a refined understanding of solute partitioning in the critical zone necessary to improve process-based transport modeling. / Doctor of Philosophy / Earth’s near-surface environment sustains nearly all terrestrial life, yet this critical zone is threatened by the environmental migration of new and potentially harmful pollutants produced to support a growing human population. Additionally, traditional mathematical methods fail to accurately describe the behavior of these emerging pollutants in soils due to complex flow patterns. Thus, scientists need to better understand how these pollutants contaminate water bodies in the critical zone. We first conducted a greenhouse experiment to understand and measure the amount of the neonicotinoid insecticide thiamethoxam (TMX) that could move from coated corn seeds through the soil environment. Water draining from fine-textured soil had >100 times more TMX than water draining from course-textured soil, due to commonly occurring fractures/cracks in the finer-particle soil and more evaporation from soil and plant leaves sequestering TMX in the sandy soil. Growing plants amplified TMX movement through soil voids to lower depths. We then conducted a field study to determine how much TMX could move to the surrounding environment throughout the corn growing season. We found that plants aided in downward movement of TMX yet restricted total losses from the plot overall by removing soil water. Our third study investigated the degree to which chemical pollutant properties control movement of solutes when water flows preferentially through soil void space. Common dairy manure was spiked with eight pollutants ranging in chemical attraction to soil and was added to an agricultural field. After irrigation, we found that when total drainage water was less than 20% derived from preferential flow, chemical properties had a negligible effect on the amount of pollutant in draining soil water. Contrary to conventional understanding, when draining water contained more than 20% preferential flow, chemical properties had a strong influence on the amount of pollutant detected. Altogether, we provide new understanding of how solutes move though the critical zone. These findings are necessary to create mathematical tools that more accurately depict pollutant behavior below-ground.

A water-filled geomembrane tube is considered for the purpose of temporary flood protection. With proper design, this tube can be a cheap and efficient breakwater, temporary levee, or cofferdam. This thesis considers a single tube resting on clay and sand foundations. A finite difference program, FLAC, is used in the numerical analyses. The tube is assumed to be infinitely long, and it is modeled two-dimensionally. Beam elements are used to model the tube. The tube is inflated with water. The hydrostatic pressure in the tube is converted to point loads and applied at the beam nodes in the direction perpendicular to the chord connecting two adjacent nodes. Two of FLAC's built-in soil models are used: elastic and Mohr-Coulomb. The Mohr-Coulomb model is used in all the cases except the preliminary analyses, in which the elastic soil model is used. The Mohr-Coulomb soil model is able to model the soil's nonlinear stress-strain and path-dependent deformation behavior. A tube without external water is placed on clay with various shear strengths to study how the clay consistency affects the height and the stresses in the tube. A tube with external water on one side is placed on medium dense sand. A wooden block is placed on the side opposite the floodwater. Three types of block geometry and two sizes are studied. The floodwater level is increased until the system fails. Three failure modes, rolling, sliding, and piping, are studied. The effect of pore pressure on these failure modes is examined. The influence of a filter placed under part of the tube and block is also investigated. The tube's tensile forces, shear forces, moments, and settlements are included. Soil stresses and pore pressures at the soil-tube interfaces are computed. The cross-section of the tube at various external water levels, and the pore pressures in the soil, are calculated. These results are compared with experimental results that were obtained by graduate students in geotechnical engineering at Virginia Tech. / Master of Science

Little is known about the original properties of soils in the East. Eight virgin soils and associated southern Appalachian hardwood vegetation were studied in western North Carolina. The study sites ranged in elevation from 720 to 1200 m on steep slopes. Overall these soils are quite deep and highly weathered due to high rainfall (>200 cm) and soluble feldspathic parent material. Organic matter contents of the surface·horizons were quite high (4.5 - 16 %), and they contained moderate to strong crumb structure. All but one soil contained cambic subsurface horizons and were either Typic Haplumbrepts or Umbric Dystrochrepts. The majority of soils in the watershed are formed in colluvium, but significant amounts of residual soils occur on sideslopes, and appear to be quite stable. The present day landforms appear to be the result of periglacial activity. North-facing soils were higher in whole soil clay, organic matter, and A horizon exchangeable cations than south-facing soils. Cation exchange capacity in these soils is almost totally dependent on organic matter content, and the mineral fraction is relatively inert. All soils were in the oxidic mineralogy class. Bibbsite was common throughout all soils and hydroxy-interlayered vermiculite (HIV) is the dominant clay-sized phyllosilicate in surface horizons. Kaolinite was low in all soils, but was more abundant on south-facing slopes. The silt fractions and sand fractions contained significant quantities of weathered 2:1-type minerals The vegetation varied from mixed-mesophytic cove hardwoods on north-facing slopes to mixed oak-hickory and oak-pine on south-facing slopes. Many trees in coves exceed 1.3 m in diameter and 50 m in height. Total litter production averaged 3494 kg/ha, and the litter layers were typified by thin leaf (L), and well developed fermentation (F) and humus (H) layers. Cations and P are concentrated in the litter layers and immediate surface soil, while N is mixed deep into the profile. Due to their oxidic mineralogy, low CEC, decreasing clay content with depth, and concentration of cations and P in litter and standing biomass these soils highly resemble tropical Oxisols. / Ph. D.