Relationships between soil hydraulic parameters and induced polarization spectra

Spectral induced polarization is a promising method to estimate soil hydraulic properties relatively quickly without interfering with the subsurface. It is essential for the interpretation of the spectral induced polarization data to understand the relationships between soil hydraulic properties and the parameters obtained from spectral induced polarization measurements. Recent studies often relate to certain types of unconsolidated sediments, e.g., artificial mixtures of sand and clay, or refer to particular pairs of soil hydraulic and complex electrical parameters. In the present study, we investigated seven samples of natural soils and a pure sand sample in the laboratory by spectral induced polarization and soil hydraulic measurements. After examining single combinations of parameters that can be expected from theoretical considerations, we calculated the correlation coefficients for all available pairs of complex electrical and soil hydraulic parameters. Based on this, two new empirical relationships are proposed and discussed in more detail. First, a linear relationship between the van Genuchten-Mualem parameter α and the inverse of the normalized chargeability m is described. Second, a power law was found to estimate the saturated hydraulic conductivity K_s from the DC resistivity ρ₀, the normalized chargeability m_n, and the fluid conductivity σ_w.