Pore fluid properties and compressibility of kaolinite

Compression test results of kaolinite with water and nine organic fluids of a wide range of dielectric constants are presented in this paper. As the dielectric constant was increased from approximately 2 in nonpolar fluids to 80 in water, void ratio and compression index of the kaolinite decreased first, reaching a minimum at a dielectric constant of 24 in ethanol, and then increased. The swelling index also increased with the dielectric constant. The effects of the pore fluids are chiefly attributed to van der Waals attractive force. When the attractive force is large, shearing resistance at interparticle contacts is large, enabling soil particles to form an open-flocculated structure with large void ratio and compressibility. Efforts were made to accurately compute the attractive force for the kaolinite in the test fluids. Its variation with the dielectric constant agreed with the variation of compressibility qualitatively and compared with experimental results on stability of kaolinite/fluid suspensions reasonably well. Double-layer repulsive forces were also found to influence the compressibility slightly. Due to an increase in double-layer thickness, the compressibility increased with a decrease in electrolyte valence and concentration. The test results also indicate that the physicochemical effects diminish with an increase in overburden stress. Under an overburden stress of 300 kPa, pore fluid properties had essentially no effect on the compressibility of the kaolinite.