The dissertation focuses on characterization of subpixel variability within a satellite-based remotely sensed coarse-scale soil moisture footprint. The underlying heterogeneity of coarse-scale soil moisture footprint is masked by the area-integrated properties within the sensor footprint. Therefore, the soil moisture values derived from these measurements are an area average. The variability in soil moisture within the footprint is introduced by inherent spatial variability present in rainfall, and geophysical parameters (vegetation, topography, and soil). The geophysical parameters/variables typically interact in a complex fashion to make soil moisture evolution and dependent processes highly variable, and also, introduce nonlinearity across spatio-temporal scales. To study the variability and scaling characteristics of soil moisture, a quasi-distributed Soil-Vegetation-Atmosphere-Transfer (SVAT) modeling framework is developed to simulate the hydrological dynamics, i.e., the fluxes and the state variables within the satellite-based soil moisture footprint. The modeling framework is successfully tested and implemented in different hydroclimatic regions during the research. New multiscale data assimilation and Markov Chain Monte Carlo (MCMC) techniques in conjunction with the SVAT modeling framework are developed to quantify subpixel variability and assess multiscale soil moisture fields within the coarse-scale satellite footprint. Reasonable results demonstrate the potential to use these techniques to validate multiscale soil moisture data from future satellite mission e.g., Soil Moisture Active Passive (SMAP) mission of NASA. The results also highlight the physical controls of geophysical parameters on the soil moisture fields for various hydroclimatic regions. New algorithm that uses SVAT modeling framework is also proposed and its application demonstrated, to derive the stochastic soil hydraulic properties (i.e., saturated hydraulic conductivity) and surface features (i.e., surface roughness and volume scattering) related to radar remote sensing of soil moisture.

Thesis (M.C.E.)--University of Delaware, 2009. / Principal faculty advisor: Christopher L. Meehan, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Dissertation : Botany : Chicago : 1916. / "Bibliographie": p. 29-31.

Thesis (Ph. D.)--University of Queensland, 2001. / Accompanying CD-ROM, entitled MINErosion model, catalogued separately. Includes bibliographical references.

Thesis (M. Agr. St.)--University of Queensland, Gatton, 2002. / Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 339-350).

Past studies on soil nailing have a common assumption that a soil nail could be simplified as a single material solid cylinder. However, a soil nail is a composite material and consisted of the following basic components: steel bars, cement grout, PVC centralizers, steel couplers, and a plastic hose, etc. They are combined and work together to keep the fundamental functions in soil reinforcement. Since these components are made by various constituent materials, the physical and mechanical properties of them are greatly different, making the deformations through soil nail diverse. The different deformations could be incompatible, which has significant effects on the soil nail integrity and performance due to the intrinsically existing vulnerable areas. One critical issue is the key component cement grout sleeve, functioning as the adhesive to transfer stress between the ground and steel bar, may encounter tensile failure on the out-layer surface or along the interface between steel bar and itself. The consequence would be cracking and detachment of cement grout and then malfunction of soil nails. Therefore, it is of great importance to examine the mechanical behavior of soil nails by taking into account the behavior of the different components. In this research extensive laboratory tests have been carried out to examine and quantify the mechanical properties of soil nail’s each component as well as their simple combinations. Based on this, a series of physical modeling of soil nail in tension and bending tests are designed to simulate the deformation of soil nail under loading. The characteristics of soil nail’s overall behavior and cracking initiation/propagation in cement grout are observed and interpreted. Besides, two soil nail’s component replacement trials based on the conventional design are conducted with attempt to enhance the overall soil nail strength and facilitate the installation procedure. A new concrete mix design with fine aggregates (sands) is adopted to substitute the neat cement grout for minimizing the local failure in cement column. Optimum sand ratio which is sound for postponing the cracking is evaluated as well. Another trial is the application of hollow core steel bar in place of the solid one. Compared to the traditional drill-and-grout soil nailing method, this new technology has advantages of fewer installation steps through a self-grout method. Similar laboratory tests are done to exam the impact on soil nail’s capacity from this change and preliminarily evaluate the feasibility of using of hollow core steel bar in practice. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

This study focuses on flow-induced bank erosion on the Red River. The study includes field measurements, experimental testing, and numerical simulation. Soil samples from the riverbank were collected at seven sites and their erodibility parameters were estimated through laboratory testing. The hydraulic shear stresses applied to the river reach were obtained by developing a 2D numerical model. Erosion rates for these sites were modeled using a linear excess shear stress equation. A bank monitoring and total suspended sediment investigation were also conducted to assess the erosion and deposition rates and patterns. The locations susceptible to erosion were determined and the periods during which these processes are likely to occur were estimated. The numerical modeling and soil testing results show that most of the time, the magnitude of flow shear stresses exerted on the bank are less than the soil sample critical shear stresses. Therefore, without considering other bank widening mechanisms as well as their interactions, the fluvial bank erosion (in isolation) should not be a significant process. However, bank monitoring shows significant bank erosion. It is recommended that the effect of subaerial processes (especially freeze-thaw) be investigated further to determine their effects on flow-induced erosion. The monitoring results convincingly show that climate-related phenomena influences cohesive soil structures and consequently, a soil’s cohesive resistance forces are significantly reduced. Therefore it can be concluded that subaerial mechanisms play a significant role in widening the banks of the Red River. / February 2016

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