Prediction for swelling deformation of fractal-textured bentonite and its sand mixtures in salt solution

Swelling deformation tests of Kunigel bentonite and its sand mixtures were performed in distilled water and NaCl solution. The salinity of NaCl solution has a significant impact on the swelling properties of bentonite, but not on its surface structure. The surface structure was characterized using the fractal dimension D-s. Based on the fractal dimension, a unique curve of the e(m)-p(e) relationship (e(m) is the void ratio of montmorillonite and p(e) is the effective stress) at full saturation was introduced to express the swelling deformation of bentonite-sand mixtures. In mixtures with a large bentonite content, the swelling deformation always followed the e(m)-p(e) relationship. In mixtures with a small bentonite content, when the effective stress reached a threshold, the void ratio of montmorillonite e(m) deviated from the unique e(m)-p(e) curve due to the appearance of a sand skeleton. The threshold of vertical pressure for mixtures in different solutions and the maximum swelling strains were estimated using the e(m)-p(e) relationship. The good agreement between estimates and experimental data suggest that the e(m)-p(e) relationship might be an alternative method for predicting the swelling deformation of bentonite-sand mixtures in salt solution.