HR: 09:30h
AN: H21G-06    [Abstracts]
TI: Spectral Induced Polarization of Saturated and Unsaturated Triassic Sandstone
AU: * Binley, A
EM: A.Binley@lancaster.ac.uk
AF: Lancaster University, Department of Environmental Science, Lancaster, LA1 4YQ United Kingdom
AU: Fukes, M
EM: m.fukes@lancaster.ac.uk
AF: Lancaster University, Department of Environmental Science, Lancaster, LA1 4YQ United Kingdom
AU: Slater, L
EM: lslater@andromeda.rutgers
AF: Rutgers University, Department of Earth and Environmental Sciences, Newark, NJ 07102 United States
AU: Cassiani, G
EM: giorgio.cassiani@unimib.it
AF: Universit… di Milano - Bicocca, Dipartimento di Scienze Geologiche e Geotecnologie, Milano, 20126 Italy
AB: Over the past decade there has been a significant increase in interest in the use of induced polarization (IP) for hydrogeological investigations. This has been driven by the realization that the IP response is potentially linked to hydraulic properties of a porous medium, since lithology, together with chemical and physical characteristics of the pore fluid interface control the IP processes. Whilst attempts have been made to demonstrate empirical and theoretical relationships between saturated hydraulic conductivity of soils and IP behavior, the focus here is on the link between pore size distribution and the frequency dependence of IP. Such a link may reveal a correlation of parameters describing moisture retention and relaxation of electrical impedance, with obvious potential value for characterization of unsaturated flow parameters. Furthermore, the relationship between spectral IP and moisture content in soils has been largely overlooked and yet may offer useful insight into hydraulic processes operating in the vadose zone. To address these issues, a study of spectral IP in samples of saturated and unsaturated Triassic sandstone has been carried out. Impedance spectra have been analyzed using macroscopic relaxation models and compared with physical measurements of rock samples (pore size distribution, particle size distribution, SEM, hydraulic conductivity). Electrical data were acquired over the frequency range 0.01 Hz to 1000 Hz on plugs drilled horizontally and vertically in samples of core with lithological contrasts. The spectra exhibit Cole-Cole type relaxations with distinct phase angle peaks. The relaxation curves are seen to vary with pore size distribution, in particular the relaxation time constant appears correlated with a measure of characteristic pore throat size. Under varying levels of water saturation, changes in relaxation are observed. Most notable is the decrease in relaxation time constant with reducing levels of saturation, caused by the variation in dominant wetted pore throat size under different degrees of saturation. Furthermore, coarse-grained samples reveal much steeper changes in time constant with saturation than fine-grained samples. The results add further evidence of useful links between IP measurements and key hydraulic properties, the value and limitations of which are discussed.
DE: 5109 Magnetic and electrical properties
DE: 1829 Groundwater hydrology
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting