Investigation on Soil–Water Characteristic Curves of Untreated and Stabilized Highly Clayey Expansive Soils

The examination of hydromechanical behavior of expansive soil lies mostly within the unsaturated soil mechanics framework, which renders the study of its soil water characteristic curve (SWCC) a necessity. This paper evaluates the correlations of two physicochemical properties, pH and surface conductance, with the behavior of the SWCCs of four natural expansive soils and four stabilized soils. The effects of chemical stabilization and curing time on the SWCCs are also analyzed. The SWCCs and the corresponding parameters were obtained from pressure plate tests and a fitting model. It was found that pH and surface conductance together showed a good correlation with the air-entry related parameter, α, because they determine the formation of the diffuse double layer around fine particles or aggregates. The macroscopic behavior, in terms of unconfined compressive strength, free swell and swell pressure at optimum moisture content (OMC), was also evaluated and good correlations of these property values with the matric suction values at OMC were observed for the four natural untreated soils, while no correlation existed for the stabilized soils. The results and the discussion provide new insight to address physicochemical mechanisms that determine the macroscopic behavior of expansive soil.