Effects of Bentonite Content on Electrical Resistivity of Soils

Abstract

Resistivity imaging (RI) is a convenient method to determine subsurface profile in a non-invasive way. This method utilizes electrical potential difference at varied subsoil conditions. Electrical conduction in soil occurs due to the presence of moisture and surface charge. Furthermore, soil-water interaction depends on the surface charge of clayey soil. Therefore, electrical resistivity responses vary with different soil minerals. However, very limited studies have been conducted to identify the effects of mineral content on electrical resistivity. The objective of the current study was to determine the variation in electrical resistivity at different weight percentages of Na and Ca bentonites. Clay minerals were artificially mixed with fine sands at an increment of 20% to determine the effect of mineral contents on resistivity. A total of 10 artificial soils with different bentonite-sand combinations were utilized in this study. In each case, resistivity test was conducted at varied moisture content and dry unit weight. According to the test results, resistivity decreased from 14.4 to 8.8 Ohm-m for an increase of Na-bentonite content from 20% to 100% at 40% degree of saturation. In case of Ca-bentonite, resistivity decreased from 29.2 to 10.1 Ohm-m for an increase in mineral content from 20% to 100%. Similar trends were observed when plasticity index (PI) and cation exchange capacity (CEC) of artificial soils were plotted against observed resistivity. Based on the test results, it was obtained that the presence of bentonite significantly affected electrical resistivity of soils.