Quantitative evaluation of the relative permittivity of artificial soil with altered soil types and water content

Abstract

To utilize the underground space more efficiently in cities, it is necessary to identify the positions of the buried structures. A ground penetrating radar (GPR) is often used to estimate the positions of such structures. However, the accuracy of depth estimation is reduced as a result of the difference between the actual and assumed relative permittivity. Therefore, estimation of relative permittivity on the basis of soil property is crucial. In an effort to determine the relationship between relative permittivity and soil properties in this study, we evaluated soil properties of artificially-altered soil types and their water contents using Vector Network Analyzer and Impedance Analyzer. As a result, the relative permittivity is found to increase with increase in water content. The possible range of the relative permittivity varies depending on the soil type because possible range of water content also varies. Moreover, the water content can be estimated under conditions in which the soil type and pore water resistivity are clear. However, the relative permittivity and soil resistivity do not correlate. With these results, we can calculate the appropriate relative permittivity of the exploration site's soil property by simple digging or using moisture sensors, thereby enabling highly accurate depth estimates of underground structures.