Spectral Induced Polarization Measurements on Unsaturated, Unconsolidated Sediments

Understanding the Spectral Induced Polarization (SIP) response to saturation is required to improve application of this geophysical technique in the vadose zone. SIP measurements (0.11000 Hz) were conducted on three unconsolidated sediments during evaporative drying. Sample grain size distribution was determined from laser particle size diffraction measurements. The dependence of the real and imaginary conductivity components on frequency and degree of saturation was determined. Both conductivity components exhibit an Archie-type power law dependence on saturation. However, the imaginary conductivity is less dependent on saturation. We find that, for each sample, the low frequency imaginary (surface) conductivity saturation exponent is approximately about half the low frequency real (bulk) conductivity exponent. The dependence of the imaginary conductivity exponent on frequency depends on sample type. For a fine sample, the imaginary saturation exponent is effectively frequency independent. For a coarse sample, the imaginary conductivity saturation dependence decreases above 10 Hz. This is tentatively related to the difference in the size of polarizable pores within each sample.