Abstract: The dielectric property of loess and the reflection mechanism and law of ground penetrating radar (GPR) wave are studied in this article. Through tests on the relative permittivity and conductivity of unsaturated loess, the inner relation between relative permittivity and three phases (gas, liquid, and solid) is analyzed. Moreover, the mathematical-physical relations of relative permittivity versus compaction degree and moisture content are obtained. The influence of GPR antenna frequency on the moisture content-permittivity relation is also analyzed. Results suggest that relative permittivity of unsaturated loess is positively related with moisture content and compaction degree; given the same loess sample, relative permittivity is positively related with antenna frequency. In addition, the interface reflection numerical model of relative permittivity versus moisture content is built, indicating that echo intensity of GPR grows with the increase of moisture content. The above conclusions are of guiding significance for GPR detection of unsaturated loess engineering.

Key words: unsaturated loess, ground penetrating radar, relative permittivity, moisture content, finite-different time-domain forward, interface reflection