Abstract
<p>A mathematical model of water diffusion in the vadose zone has been implemented for different types of soil textures in order to determine the soil water content (SWC) profiles in dependence of depth and time. From these profiles, obtained for different soils, we derived the characteristic electrical parameters, such as relative permittivity (<span class="gt-card-ttl-txt">epsilon</span><span><sub>r</sub></span>) and electrical conductivity (<span>sigma</span>), and their variation in time, employing empirical relations available in the scientific literature. The simulation through mathematical models has been performed taking into account different types of soils characterized by the percentage composition of sand, clay and silt in the textural triangle, which provides some physical and chemical properties that affect the water retention in the soil. The resulting simulated profiles of SWC and consequently permittivity and conductivity profiles, span over a certain range of values suggesting the best techniques and the limits in geophysical investigation. Moreover this a-prior knowledge helps in the elaboration and interpretation of permittivity and conductivity data obtained by the measurements. Permittivity and conductivity profiles are particularly useful in some environmental applications when the soil textures are (or supposed to be) known as in the typical case of landfill leachate dispersion. Since the soil textures beneath or nearby a disposal waste are characterized by a SWC, the values of (<span class="gt-card-ttl-txt">epsilon</span><sub>r</sub>) and (sigma) at various depth can be directly inferred.</p>
Highlights
Electrical conductivity (v) and relative dielectric permittivity are two independent physical properties that characterize the behavior of soil when excited by electric currents or electromagnetic fields [Settimi 2011]
The electrical conductivity and dielectric permittivity of the constituent minerals are the main controlling factors of the electrical properties of soils [Kriaa et al 2014]. The derivation of these quantities related to the water content provides useful information regarding the practical use of geophysical investigation (GPR, time-domain reflectometry (TDR), etc.), applied to unsaturated subsurface vadose zone of medium
The picture obtained by the modeling software, shows range of water content up to 50%, and the relative permittivity and electrical conductivity values linked to it, plotted in a 3D space
Summary
Electrical conductivity (v) and relative dielectric permittivity (fr ) are two independent physical properties that characterize the behavior of soil when excited by electric currents or electromagnetic fields [Settimi 2011]. The electrical conductivity and dielectric permittivity of the constituent minerals are the main controlling factors of the electrical properties of soils [Kriaa et al 2014] The derivation of these quantities related to the water content provides useful information regarding the practical use of geophysical investigation (GPR, TDR, etc.), applied to unsaturated subsurface vadose zone of medium. Hydrogeological properties (physical and chemical) are important since they dominate the electric properties of soil, described by the two quantities v and fr These last quantities can be directly measured through several techniques or theoretically deduced (constitutive relations) in a homogeneous medium. In this paper these parameters are estimated through soil hydrologic models [Huisman et al 2003] In the latter case the SWC in vadose zone plays an important role to determine both relative permittivity and electrical conductivity since they are strongly dependent on it. It could represent a preliminary phase which precedes the measurements and facilitates the interpretation of the results (GPR, TDR, ERT and other similar geophysical investigation techniques e.g. after raining survey or in landfill control)
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