Review of Archie's equation through theoretical derivation and experimental study on uncoated and hematite coated soils

• Archie's equation (EC = electrical conductivity) was reviewed theoretically.
• EC of uncoated and hematite (iron oxide) coated sands and clay was measured.
• EC of hematite coated and uncoated sands showed good agreement.
• EC of hematite coated clay indicated a somewhat higher value than that of uncoated.
• Increase in EC of coated clay was attributed to the increased surface conduction.

This theoretical and experimental study investigated the applicability of Archie's equation to iron oxide coated soils as a function of pore water chemistry, with the ultimate goal of developing a relationship to estimate electrical conductivity based on the physical properties of soils. The study performed an experimental investigation to quantify the electrical properties of uncoated and lab-prepared iron oxide coated sands and clay, in order to evaluate the role of sorbed hematite on the measured electrical conductivity/resistivity of the soils. It was demonstrated that the observed conductivity/resistivity of hematite coated and uncoated clean sands showed good agreement under the tested salinities and iron contents, and both coated and uncoated sands could be represented by Archie's equation. In contrast, the electrical conductivity of iron oxide coated clay indicated a slightly higher value than that of clean kaolinite at low salinity due to the higher relevance of surface conduction; however, with further increase in salinity, the electrical properties of both coated and uncoated kaolinites were comparable and governed by pore water conduction, which agreed with the prediction from Archie's equation.