Abstract

To provide a database for interpreting GPR field data by means of small-scale laboratory studies, we have determined the real and imaginary parts of the dielectric permittivity of fine-grained fractions of soil samples from eastern Spain in the laboratory. We use the parallel-plate method in combination with an impedance analyzer and focus on the frequency of 200MHz. The measurements are compared to physical properties such as volumetric water content, dry density, clay fraction, and carbonate content. The results show the well-known increase in dielectric permittivity with increasing water content, as presented in the literature; however, our values are systematically higher. This deviation may be caused by the exceptionally high carbonate content of the samples. We establish a basic relationship between dielectric permittivity and water content that is characteristic for soils in the research area. In addition to the dominating influence of water on permittivity, we find a correlation with dry density as well, which is linear for dry samples. Finally, we calculate the attenuation coefficients and find high attenuation for samples with high clay fraction, even at low water contents. A 1D model of the permittivity distribution is constructed from borehole data (water content and layer thickness) coincident with a GPR profile and from the laboratory data. The modeled GPR trace explains the observation and thus connects laboratory measurements to GPR data.

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