| A comprehensive experimental and analytical study of the complex dielectric response of moist soils over the 100 MHz-18 GHz frequency range was undertaken. The experimental setup included a square cross-section coaxial sample holder and a vector network analyzer system for signal generation and detection as well as an external bath for sample temperature control. Soils chosen for study included a poorly-graded Ottawa sand, a clean well-graded tan sand, a clean poorly-graded silt, and a nearly-pure non-swelling clay mineral, kaolinite. Complex dielectric constant data for these soils were collected at ten different temperatures ranging from ;Two model interpretations were applied to the data. One was an equivalent circuit that contained separate soil and water elements. This circuit simulated both low frequency and high frequency loss mechanisms, and the elements were arranged to represent both series and parallel electrical response of the soil constituents. The second model assumed a fractal pore structure for small pore spaces and hypothesised that the critical volumetric moisture content at which the soil dielectric response went through a transition from series to parallel behavior was equivalent to the field capacity of the soil. Testing of this hypothesis against the soils used in this study led to the conclusion that the small-pore fractal dimension of soils tends toward 2.0 for coarse substances like the clean sands and toward 3.0 for very fine substance like the kaolinite, with normal soils falling in the 2.5 to 2.7 range. |
