Abstract

The spectral electrical responses (SER) of sand and clay mixtures subjected to an effective stress of 20 MPa and saturated with varying concentrations of NaCl are measured in a laboratory environment in the frequency range 10−2 to 104 Hz. Changes in clay content and fluid concentrations result in characteristic changes in amplitude and phase spectra. The equivalent circuit model due to Dias is used to characterize the spectral electrical behavior of the saturated mixtures. Two circuit elements of Dias model, the electrochemical parameter η, and the dimensionless parameter δ, are particularly sensitive to the amount of clay and the concentration of the pore fluid. The electrochemical parameter η is shown to increase significantly with an increase in clay content when the soil sample is saturated with freshwater. The dimensionless parameter δ on the other hand is directly related to the concentration of the pore fluid solution (NaCl), increasing with an increase in fluid concentration. Effects of electrode polarization on the SER measurements are modeled and minimized by addition of a Warburg diffusion element term to the equivalent circuit model of the sample.

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