A combined use of Archie and van Genuchten models for predicting hydraulic conductivity of unsaturated pyroclastic soils

• Electrical resistivity vs. hydraulic conductivity relationship is investigated.
• Empirical laws are used for estimating electrical–hydraulic parameters.
• A direct relationship is found between hydraulic and electrical conductivity.
• The relationship is used to characterize unsaturated pyroclastic soils.

Hydrogeophysics has been developing in recent years to improve characterization and monitoring of saturated/unsaturated aquifers, through the combination of geophysical and hydrogeological methods. To exploit the potential benefits of this integration, definition of petrophysical relationships that allow the translation of geophysical data into hydrogeological parameters (and vice versa) is essential. In this paper, Archie's and van Genuchten's models, which relate electrical resistivity and hydraulic conductivity to the degree of saturation, are combined to obtain a closed-form link between hydraulic conductivity and electrical resistivity. Such an expression is used to characterize pyroclastic deposits covering Sarno Mountains (southern Italy), which are often affected by landslide phenomena. As expected, an inverse relationship is found between hydraulic conductivity and electrical resistivity due to predominance of the electrolytic component over the interfacial component of the electrical conductivity. The variability of the hydraulic conductivity marks out the texture of the investigated pyroclastic horizons. Finally, a hydraulic conductivity–matric suction relationship is retrieved by using an empirical correlation between electrical resistivity and matric suction.