Effect of Solution Composition on the Swelling of Extracted Soil Clays

For soils containing expansible minerals, the swelling of extracted soil clays in mixed NaCl‐CaCl 2 solutions was well correlated with relative hydraulic conductivity of the soils to the same solutions, and with theoretical interlayer swelling values based on a “domain” model. In this model, mixed Na‐Ca clays were considered to consist of discrete Na‐ and Ca‐regions, with only the Na‐regions swelling at low salt concentrations. The correlations suggest that the most plausible mechanism for hydraulic conductivity decreases in soils containing significant amounts of expansible minerals is the closing of conducting pores by insitu mineral swelling. However, a dispersion process activated by the interlayer swelling of expansible minerals would also be compatible with the data.