Spectral electrical response measurements and petrophysical characterization of soils

The influence of soil structure and composition on the spectral electrical response, (SER) of soils is analyzed based on laboratory measurements and modeling studies are done to investigate the relationship between model parameters and physical properties of the soils. Measurements of the resistivity amplitude and phase of natural and artificial soil samples are made at frequencies from 10−2 Hz–10kHz. These measurements are correlated with modifications of soil structure effected by systematic changes in applied stress, pore fluid chemistry, particle size distribution, clay content, and chemical reactions. The determination of these physical properties and the effect of various contaminants on natural soil samples based on information obtained from SER measurements is shown to be feasible.; Based on these laboratory measurements and modeling studies, empirical relationships are presented between SER, applied effective stress, porosity and hydraulic conductivity for clean sands. It is shown that the parameters η and δ characterizing the SER are directly related to clay content and pore fluid salinity respectively, for sand-clay mixtures in the laboratory. Regression equations are shown to relate the parameters of the multi-Cole-Cole model directly to porosity and hydraulic conductivity for 25 natural soils. The results of long-term laboratory measurements of contaminated natural soils show how the changes over time in the SER can be used to identify and monitor contaminants in the subsurface. This work may provide geoscientists with a rapid and inexpensive means of characterizing the subsurface and monitoring changes in the properties of soils over time. The technique is non-invasive, which is particularly desirable for environmentally sensitive areas or hazardous contamination sites.