Katherine Klein

Electrical Conductivity in Soils: Underlying Phenomena

Electrical conductivity can be accurately and readily measured in the laboratory and in the field, with minimal electrode effects even in high specific surface soils and∕or high ionic concentration pore fluids. Electrical conductivity combines the contributions of particle conduction, surface conduction and pore fluid conduction, and the effects of particle shape and fabric. The interplay between participating soil parameters is often obscured in typical empirical equations, such as Archie’s law. New experimental results show that surface conduction is an important contributor to global soil conduction in high specific surface soils that are saturated with low-ionic concentration pore fluids; the relevance of surface conduction increases with decreasing porosity. On the other hand, pore fluid conduction prevails as the conductivity of the electrolyte and the porosity of the soil increase. Furthermore, low frequency conductivity anisotropy increases with increasing ionic concentration. Simple yet robust mi...

Electromagnetic Properties of Cemented Paste Backfill

The effect of specimen composition on the physicochemical processes in cemented paste backfill is studied using small perturbation electromagnetic waves. The factors that are tested include binder type and content, selected chemical admixtures (superplasticizers), mineral additives (e.g., fly ash), and pore fluid chemistry (e.g., ionic concentration and pH). Two measurement techniques are used: a two-electrode capacitor-type system at low frequencies (100Hzto100kHz) and an open-ended coaxial termination probe at high frequencies (200MHzto1.3GHz). The electromagnetic measurements are sensitive to changes in the CPB composition. The temporal variations in the effective conductivity reflect the various hydration stages, while the decrease in the real relative permittivity with time is due to a reduction in free water content.

Permittivity Measurements of High Conductivity Specimens using an Open-Ended Coaxial Probe—Measurement Limitations

Non-destructive electromagnetic wave-based techniques have been used for over a century to gain insight into the behaviour of geomaterials. The technique used in this study is a high frequency (20MHzto1.3GHz) open-ended coaxial probe measurement system. This study highlights the importance of knowing the limitations of the measurement system. The specimens that are tested are aqueous solutions of NaCl, CaCl2, and FeCl3 with conductivities ranging from approximately 10−3to8S∕m. Real permittivity data of the high conductivity specimens show a relaxation phenomena at MHz frequencies where none exists, indicating that electrode polarization is occurring. The frequency at which electrode polarization begins to manifest (e.g., limiting frequency) increases as the specimen conductivity increases. An empirical relationship between the limiting frequency and specimen conductivity is presented and is applied to three kaolinite-NaCl slurries. Additional problems associated with measuring high conductivity specimens ...

Towards a Better Understanding of the Electro-Magnetic Properties of Soils

Given the sensitivity of soils to disturbance, the use of low perturbation (i.e., non-destructive) electromagnetic waves provides a viable option for studying soil properties. The measured parameters during the excitation of a material by an electromagnetic wave are electrical conductivity, dielectric permittivity, and magnetic permeability. Electrical conductivity is a measure of charge mobility in response to an electrical field. Dielectric permittivity represents the polarizability of a material. Magnetic permeability indicates the degree of magnetic dipole alignment within a material under the excitation of the magnetic field. Factors that affect electromagnetic wave parameters include water content/degree of saturation, porosity, spatial distribution of the phases (e.g., anisotropy), particle properties (e.g., specific surface), pore fluid characteristics, and temperature. This paper presents a review of electromagnetic parameters, provides experimental data showing the impact of the various factors on the electromagnetic response, and gives a physical explanation of why these factors affect electromagnetic properties. Finally, various applications of electromagnetic wave-based techniques are presented, including monitoring the diffusion of salt through a soft kaolinite sediment and the hydration process in cemented paste backfill.