Abstract: XRD test, permeability test, thermal analysis test and scanning electron microscope (SEM) were performed to investigate the effect of CaCl₂ solution on the permeability coefficient of red clay. The red clay specimens were saturated by CaCl₂ solutions of different concentrations (0.0, 0.1, 0.3, 0.5 and 1.0 mol/L). Results reveal that when the pore solution concentration increases from 0.0 mol/L to 0.5 mol/L, the permeability coefficient of red clay decreases before increasing. Afterwards, the permeability coefficient presents a decreasing trend with the increase of pore solution concentration. Through thermal analysis tests, the content of strongly bound water of red clay saturated with different concentrations of CaCl₂ solution was obtained. The changes in the content of strongly bound water is closely related to the change of permeability coefficient of red clay. The microstructure of soil samples in different concentrations of CaCl₂ solution was observed by scanning electron microscopy (SEM). Ca²⁺ increases the thickness of the mineral-bound water film of the red clay, which leads to the declining of effective pore space, thus reducing the permeability of the soil. The findings can be used as a data reference for the use of red clay as a barrier to isolate pollutants.

Key words: red clay, calcium chloride solution, permeability coefficient, XRD test, permeability test, thermal analysis test, strongly bound water