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Geophysical methods have been increasingly used to characterize the Earth's critical zone (CZ) and monitor hydrological processes occurring within it. For a quantitative interpretation, geophysical studies of CZ materials are necessary, and thus require more sophisticated laboratory setups. In this study, we develop a hydrogeophysical soil column system to measure key hydraulic and electrical properties of regolith in CZs. The developed soil column system consists of two components: (a) a novel hydrogeophysical probe that measures pore water pressure and electrical potential in soils and (b) a cylindrical cell to hold soil samples. The system can be arranged to perform both saturated flow and drainage tests. The saturated flow test is similar to the traditional constant head experiment for determining the hydraulic conductivity and streaming potential coupling coefficient. The drainage tests can produce transient responses of cumulative overflow, pore water pressure, and streaming potential. These transient data can be used to estimate the sample's electrical and hydraulic properties with the coupled, stochastic hydrogeophysical inversion. A sand sample is used to demonstrate the procedures of applying this new system. The measured saturated hydraulic conductivity and streaming potential coupling coefficient of the sand are within the typical ranges of sands reported in the literature. The inversion-estimated soil parameters can well reproduce the measured transient responses during the drainage test of the sample. Moreover, the inversion-estimated saturated properties are in good agreement with those independently measured in the saturated flow test, showing the robustness of the developed system.

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Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.