This study proposes a methodology for using dielectric spectroscopy to characterize soil properties. It mainly aims to relate the effective dielectric properties of soil with those of its constituents, i.e., solid skeleton and pore-filling fluid. Through microstructure-based simulations and coaxial probe measurements, the dependence of the overall dielectric permittivity on the permittivity of the fluid filling pores was determined. Quartz sand sample was examined using two approaches. The first of them assumed saturating pore space with several organic solvents and testing narrow-frequency response. In the second approach a single fluid, namely, propylene glycol was used and broad-frequency response was measured. Mori–Tanaka approximation and Lichtenecker’s “alpha model” were employed to computationally estimate dielectric response. Both models showed promising results for potential practical applications like groundwater contamination detection and earthen dam seepage monitoring. This research underscores the potential of dielectric spectroscopy for soil property estimation and structural monitoring in geotechnics.