Complex electrical properties of sand-clay mixtures and alluvial sediment samples

The interpretation uncertainty of DC-resistivity surveys is reduced applying Spectral Induced Polarization methods. The aim of this work is to compare the complex electric resistivity behaviour, in the frequency range from 10 mHz to 100 kHz, of saturated sand-clay mixtures prepared in laboratory and alluvial muddy sands or sandy mud samples extracted from Po plain quarries (Italy). The comparison is made on the basis of the coarse-to-fine granulometric fraction ratio, defined with a cut-off diameter of 0.063 mm. Electrical analyses are conducted within a cylindrical sample-holder equipped with impolarizable potential electrodes and results are discussed in terms of magnitude and phase spectra. Large differences in the phase spectra are observed. They are interpreted in terms of mineralogical composition, especially of the fine-grained fraction, and organic matter content. In fact, the effect of water electrical conductivity on these samples is already showed by a series of systematic tests and the textural assemblage is controlled. To evaluate the contribution of sediments' geochemical properties, data fitting through the Cole-Cole model is proposed with satisfactorily results. Since phase spectrum is quite sensitive to the fitting parameters, also a multi-objective approach that consider separately the fit of the magnitude and phase spectra has been tested.