Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xiii, 325 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 138-144).

Thesis (Ph. D.)--Washington State University. / Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1989.

Three goals of this research were: 1) to develop a field-scale research facility that could be used for conducting a variety of soil water experiments in both deep (greater than 2 meters) and near-surface soils where the soil water balance could be accurately determined; 2) to develop a transient experimental technique for calibrating time domain reflectometry (TDR) probes; and 3) to study the use of vertically-installed TDR probes for measuring near-surface soil water movement in a field setting, and to compare these measurements with those made by the weighing lysimeter. The weighing lysimeter facility consists of two lysimeter tanks, 4.0 m deep and 2.5 m in diameter, which rest atop a scale with a resolution of ±200 g, equivalent to ±0.04 mm of water on the surface. Data collection is completely automated with a data logger and personal computer. Both lysimeters are instrumented with TDR probes, tensiometers, and pore water solution samplers; thermocouples are installed in one lysimeter for measuring temperature. The TDR probes were calibrated using a transient method known as upward infiltration. The method is rapid, allows the soil to remain unchanged during the experiment, and provides many data points. The upward infiltration method was tested using two different length probes in soils of three textures. Results show that the upward infiltration method is stable, repeatable, and provides accurate dielectric constants and calibration curves. Four, vertically-installed TDR probes of different lengths (200, 400, 600, and 800 mm) were placed in the lysimeter at ground surface to measure water added and water lost during a one-month period in the presence of daily irrigated turfgrass. The purpose of this study was to compare changes in soil water storage as measured by the TDR system, against measurements made using the weighing lysimeter. The TDR probes detected diurnal changes in water content due to irrigation and evapotranspiration, even when these amounts changed slightly from day to day. The TDR probes underestimated the measurements of both water added and water loss, as confirmed using measurements from the weighing lysimeter. The presence of a 47-mm thick biomass above the TDR waveguides retained water that otherwise would have percolated the soil surface into the measurement domain of the probes. Addition and loss of water in the biomass were recorded by the lysimeter, but not by the TDR probes, thus explaining the underestimation. Modeling of near-surface water movement with the HYDRUS model showed very similar water movement behavior as measured by the TDR probes. This confirms our hypothesis that TDR would a useful tool for measuring diurnal changes in water content for irrigation scheduling.

Contaminants can enter groundwater through the unsaturated zone as dissolved solutes. To predict the location and extent of these contaminants, transport parameters such as pore water velocity y and dispersion coefficient D are required. These parameters are often obtained through transport experiments. The goal of this study is to determine y and D using time domain reflectometry (TDR) technique. Using TDR for transport experiments under unsaturated conditions, we investigated the effects of volumetric water content θᵥ, distance of flow path, and draining-wetting history on D. TDR was used to measure θᵥ, and salt concentration in twenty-one unsaturated column experiments. The 105 cm-long column was homogeneously packed with silica sand (particle size: 53 to 425 pm). Ten TDR probes at ten depths were used to obtain in situ breakthrough curves and a chloride electrode was used to measure effluent breakthrough curves at the bottom of the column. A 35 mM NaC1 (sodium chloride) was used as the tracer with 20 mM NaC1 as background solution. We developed a three-parameter expression relating θᵥ, to measured dielectric constant Kₐ: θᵥ =aKₐᵅ + b. This calibration expression fits as closely or better than the "universal polynomial" and is also consistent with the well-known mixing model. For an isotropic soil with homogeneous water distribution, this expression is further simplified to two parameters by taking α = 0.5. The effects of temperature, porosity, soil solid and bound water can be taken into account by varying a and b of the two-parameter expression. TDR measurements have been shown to be sensitive to bound water and not particular sensitive to the other factors. To calculate y and D from breakthrough curves of step-input experiments, a new moment analysis method has been developed. The transport parameters obtained from this new method show a little difference from the parameters determined from the convection-dispersion equation using the CXTFIT model (a published computer program for estimating solute transport parameters from observed breakthrough curves). Our results demonstrated that D is dependent on measurement methods and concentrations of experimental solutions.

Currently there is no consensus on how to account for the lateral earth pressures when designing drilled shaft retaining walls in expansive clay soils. Typically an equivalent fluid pressure is assumed which can range from 40 psf/ft to over 100 psf/ft. The range of assumptions currently in use can cause more than a factor of two difference in the maximum bending moment in the shaft. This range could cause the walls to be over-designed or under-designed. A full-scale test drilled shaft retaining wall was constructed on a site underlain by approximately 50 feet of the expansive Taylor Clay. Analysis of the wall is intended to provide information to be considered in design about the effects of the moisture cycles which cause shrinking and swelling. In order to monitor the moisture changes within the clay, 20 Time Domain Reflectometry (TDR) probes were installed behind the wall. This thesis discusses the monitoring plan, calibration, installation, and initial results from these probes. The objectives of this thesis is to provide information regarding the site conditions and reasons for using TDR probes for this project and to describe the monitoring plan, calibration, installation, and the field performance of the TDR probes and the moisture values that have been seen on the site to date. Previous studies show that difficulties can be expected when using TDR probes in highly plastic clays. Results from this study are typical of these results seen previously. The initial results show that 4 of the 20 probes are recording reasonable waveforms. However, the waveforms cannot be analyzed using conventional methods. This result was because the waveform reflection that indicates the end of the probe cannot be defined due to attenuation of the signal, which is typical of highly conductive soils. Also, the large amount of scatter in the electrical conductivity values does not allow for the moisture content to be correlated to the electrical conductivity. In order to use the TDR probes to measure moisture content at the project site, an alternative method needs to be employed to analyze available waveforms. If another method can be successfully employed for the functional probes, the subsequent step would involve recovering the probes that are not functioning properly in order to get a moisture profile along the full cantilevered height of the wall. Direct moisture measurements should also be taken periodically to provide a moisture profile. / text

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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Hard red duplex soils (HRDS) cannot sustain economically productive vineyards without careful management. An experiment was conducted at Rosbercon Vineyard, Picola from 1995 to 1998 in a vineyard block of Chardonnay on Ramsey rootstock planted in 1972. The hypotheses tested were: a) transient waterlogging decreases root growth and grapevine performance, and b) hardening of soil decreases root growth and grapevine performance. (For complete summary open document)