Joint Measurement Setup for Determining Spectral Induced Polarization and Soil Hydraulic Properties

Abstract

The prediction capabilities of unsaturated flow and transport models are often limited by insufficient knowledge about the structural and textural heterogeneity of the soil. To obtain more information about soil structure, texture, and heterogeneity, as well as hydraulic properties, noninvasive spectral induced polarization (SIP) measurements have shown promise. However, there clearly is a need for more detailed investigations on the relation between SIP and hydraulic properties, in particular for unsaturated soil. To address this need, we developed a novel experimental setup that allows simultaneous determination of hydraulic and electrical properties. Our setup consists of multistep outflow equipment for hydraulic measurements and an electrical impedance spectrometer for measurements of the complex electrical conductivity. Two different measurement cells were constructed. The first measurement cell can only be used for nonshrinking soil, while the other one also allows measurements on mildly shrinking soil. Test measurements showed that the measurement accuracy is very high for the complex electrical conductivity. Nonpolarizable point electrodes are used for voltage measurements, ensuring a good contact to the sample for a wide range of water saturations. An experiment performed on unconsolidated sand investigated the dependence of the complex electrical conductivity and fitted Cole–Cole parameters on water saturation. The phase values and chargeability increased with decreasing saturation. The relaxation time associated with a phase peak was independent of saturation and corresponded reasonably to the average grain size of the sand. Therefore, no relationship between relaxation time and unsaturated hydraulic conductivity was found for this well‐sorted sand.

Spectral induced polarization measurements on variably saturated sand‐clay mixtures

“…Sketch of the experimental set‐up of Breede et al . (2011): a pump is used to desaturate the sample using several pressure steps.…”

An overview of the spectral induced polarization method for near‐surface applications

“…Sample holders that are too small may prevent inclusion of larger end members of a material grain size distribution, whereas too large sample holders may suffer from inhomogeneous packing. Electrical and physical measurements should be made on the same exact sample using, where possible, multifunction sample holders (e.g., Slater and Lesmes 2002; Breede et al 2011), in order to avoid uncertainty associated with differences between samples. Temperature should be recorded and controlled and the sample should be saturated with appropriate fluids of a specified salinity/composition.…”

Complex Electrical Measurements on an Undisturbed Soil Core: Evidence for Improved Estimation of Saturation Degree from Imaginary Conductivity

“…In addition, these techniques can provide information with minimal soil disturbance and associated costs. The use of electrical resistivity for the characterization of soil moisture and pore water quality dynamics has been extensively explored (Binley et al, 1996, French et al, 2002; Garre et al, 2010; Oberdorster et al, 2010; Slater et al, 2002), while studies on the use of induced polarization in unsaturated media are relatively scarce (Breede et al, 2011; Breede et al, 2012; Schmutz et al, 2010). In contrast to high frequency ground penetrating radar methods for estimating water content from the dielectric permittivity, the low frequency electrical resistivity method offers some distinct advantages.…”