Electrical response characteristics of soil-electrolyte systems (10kHz-10MHz)

Abstract

The electrical response characteristics of saturated soils depend on soil structure, particle orientation, effective particle size and size distribution, fluid type, fluid conductivity, volume fractions, etc. The use of dispersion data in geotechnical applications is attractive because: (1) the factors that affect physicochemical properties and soil behavior also affect the electrical response; and (2) application of an alternating voltage does not alter soil properties. Many theoretical, empirical, and semi-empirical models have been proposed to describe the dispersion of soil-electrolyte systems. In general, the geotechnical engineer is interested in describing the dispersion of soil-electrolyte systems by an equivalent circuit instead of the more involved electron based models. This investigation is comprised of experimental and modeling studies on electrical response of soil-electrolyte systems including: (1) review of literature; (2) development of model; (3) development of experimental apparatus; (4) performance of experiments; and (5) comparison of model predictions with experimental data. The solid particles used in the investigation were: kaolinite, silica flour, Ottawa sand, and glass beads, and electrolytes used were NaCl, KCI, CaC'2 solutions of different concentrations. The frequencies used are in the range of 1 0 kHz-1 0 MHz. Macroscopic models for interacting and non-interacting phase mixtures were developed based on Maxwell-Wagner microscopic relaxation mechanism. Experiments were performed on different solid particles with varying electrolyte conductivities, types, and volume fractions. The investigation indicates that there is little dispersion in non-interacting phase soils. However, the dispersion is considerable for interacting phase mixtures. affected by the double layer polarizations. The comparisons of model predictions with the experimental results indicate that the developed simple electric circuit model is adequate in describing the electrical response characteristics of non-interacting phase mixtures. The response of kaolinite-electrolyte mixtures can also be described by non-interacting phase model in high frequency range. Based on the study, an in-situ measurement technique is proposed to estimate volume fraction of solids, and electrolyte conductivity from dispersion data obtained from an electrical resistivity cone penetrometer.