Changes in the characteristics of the pore fluid in soils, such as concentration, valence, and permittivity, affect the electrical properties of the bulk fluid and the formation of double layers, causes volumetric changes and alters the fabric of the soil. The complex permittivity spectrum of a clay-fluid system reflects the polarizability of the phases and their interaction. This paper presents a review of polarization mechanisms, followed by high-frequency (MHz-GHz) experimental results involving two clays of very different specific surface, aqueous electrolytes with varied concentration and valence, and non-aqueous phase liquids NAPLs. Complex permittivity measurements reveal the effect of mixing order, both in the case of electrolytes and when the clay-fluid mixture includes organic liquids. The develop­ ment of double layers is hindered when NAPLs reach clay surfaces before water. Various processes that influence the complex permittivity of geomaterials are identified. Results are relevant to the interpretation of field measurements with ground penetrating radar and time domain reflectometry.

Assessing and Monitoring the Geo-Environment

Dielectric Permittivity of Soils Mixed with Organic and Inorganic Fluids (0.02 GHz to 1.30 GHz)

The dielectric permittivity of soils can be significantly modified by the presence of organic contaminant in the pore fluid. Thus, nondestructive techniques based on the propagation of electromagnetic waves may be used to detect contaminant plumes and to evaluate decontamination processes. Ground penetrating radar (GPR) and time domain reflectometry are two of the most relevant geophysical tools working in the frequency range of interest here. In this work, the complex dielectric permittivity of some soil–organic mixtures are measured in the frequency range of 20 MHz to 1.3 GHz. Tests are conducted in samples of silica sand, loess, and kaolinite mixed with varied amount of paraffin oil and lubricant oil. Additional tests are performed in soil–water samples for comparison. Mixtures formulas reported in the literature are extended from two to three and four phases in order to model the measured dielectric response of the contaminated soil samples. The results allow us to study the effect of the volumetric l...

Complex Dielectric Permittivity of Soil–Organic Mixtures (20 MHz–1.3 GHz)

The main objective of this paper is to explore the potential application of electromagnetic waves to evaluate the effect of contaminant removal in granular soils. Thus, various specimens of saturated silica sand were prepared using paraffin oil and lubricant oil as contaminants. Four flushing fluids were used to remove the contaminants from sand columns: Deionized water, water-detergent, water-detergent-alcohol solution, and water vapor. Dielectric permittivity was measured at different stages of the removal process at the frequency from 20 MHz to 1.3 GHz. The measured permittivity was compared with that determined for clean and fully contaminated specimens. A theoretical mixture formula was calibrated and implemented to estimate the volume fraction of contaminant present in the pore fluid. It is concluded in this work that dielectric parameters reflect the contamination level of the soil for the nonpolar organic compounds used here. Measurement of permittivity allows us to determine that the inclusion of alcohol and detergent in the displacing fluid improved the removal efficiency. However, water vapor was the most efficient removal agent.

Assessing and Monitoring the Geo-Environment

Citations

Dielectric Permittivity of Soils Mixed with Organic and Inorganic Fluids (0.02 GHz to 1.30 GHz)

Complex Dielectric Permittivity of Soil–Organic Mixtures (20 MHz–1.3 GHz)

Removal of Immiscible Contaminants from Sandy Soils Monitored by Means of Dielectric Measurements

Related Papers (5)

The application of geotechnical engineering monitoring to assesment and prediction of geological hazards

Geotechnical Engineering in the Coastal Zone.

Recent Study of Coupled Processes in Geotechnical and Geoenvironmental Fields in China

Soil monitoring: Methodology and realization

GeoCongress 2008: Characterization, Monitoring, and Modeling of Geosystems