HYDRAULIC PROPERTIES OF VARIABLY-SATURATED POROUS MEDIA DETERMINED USING QUANTITATIVE NEUTRON RADIOGRAPHY

The theoretical understanding of fluids in unsaturated porous media has improved substantially over the last several decades. Water retention curves remain a central pillar in the theoretical framework for modeling of water flow in unsaturated porous media. Use of the average water retention function in models to simulate water flow in porous media can result in inaccurate predictions due to the variations in water content and matric potential with elevation within the medium. As a result, point water retention curve data are needed for testing existing numerical and analytical models and for improving our ability to predict unsaturated water flow. Traditionally point water retention functions have been derived from average water retention curve data. The main objective of this research was to directly measure point water retention functions using neutron imaging. Neutron imaging provides a non-destructive tool for visualizing water flow in porous media due to its high sensitivity to hydrogen, and relative insensitivity to mineral solids. Using neutron imaging techniques we have explored the following research topics: (1) quantitative measurements of the equilibrium water content distribution in porous media, (2) measurement of average and point water retention functions using neutron radiography, (3) assessment of analytical models relating average and point water retention curves, and (4) investigation of the dynamics of unsaturated water flow.

In the first two chapters of this dissertation we developed quantitative neutron imaging techniques to measure the 2-dimensional distribution of water in porous media and obtain the average water retention function for Flint sand by neutron radiography. In chapter III, point water retention functions were directly measured by neutron radiography and the resulting point functions were parameterized using the Brooks & Corey equation. The point water retention function constructed from the median values of the fitted Brooks and Corey parameters corresponded closely with the point curve for Flint sand obtained by inverse modeling of the average water retention curve data. In the final chapter of this dissertation we investigated capillary uptake of water in Berea Sandstone and estimated the sorptivity and unsaturated diffusivity function from analyses of the neutron radiographs.