Effect of water content and sodium sulfate concentration on the resistivity of red clay

Red clay is widely distributed globally and is closely related to human production and life. The middle reaches of the Yellow River basin in China are characterized by complex geological structures, concentrated rainfall periods. The soluble salts such as sodium sulfate enter the red clay particles along with the infiltrating water, forming a red clay-like saline soil. In order to study the effects of water and salt on red clay soils, this paper uses red clay in the Heyang of Weinan with different ratios of distilled water (10–20%) and Na₂SO₄ (0–4%), and obtains the resistivity of red clay soils at different frequencies (100 Hz–100 kHz) using an inductance, capacitance and resistance digital bridge tester. The results show that the resistivity of red clay is negatively correlated with water and salt content. With the increase of water content, the increase of conductive paths in the pore water improved the electrical conductivity of the red clay; while when the concentration of Na₂SO₄ increased, the free moving anions and cations in the pore water increased, the electrical conduction efficiency increased and the resistivity decreased. The high frequency increased the conductivity of red clay by contributing to electrical double layer deformation, whereas the electrode polarization led to inhibition of conductivity under low frequency. A negative power exponential relationship exists between the resistivity of red clay and the test frequency. This study may provide a valuable reference for the rapid identification of the physical properties of red clay and its internal structure.