Swelling reduction in bentonite due to saline solutions via fractal modeling

This study quantifies the complex impact of saline solution on the swelling behaviour of compacted bentonite or montmorillonite clay. The influence mechanisms can be divided into macroscopic mechanical action and microscopic chemical reaction, depending on the altered minerals in the bentonite. A fractal adsorption model has been introduced to depict the void ratio of montmorillonite in different saline solutions at a steady swelling state with a uniform power function. In the formulated model, the osmotic suction of saline solution (π) and vertical load (p) were classified as the macroscopic mechanical actions and were embodied by total effective stress (p^e), while the microscopic chemical reactions that fundamentally transform the composition of bentonite were reflected by the swelling coefficient (C). A calculated method for the swelling coefficients has been formulated in this study, as the fractal adsorption theory is combined with the diffused double layer theory in deionized water, that has been further validated using swelling experimental data for different bentonites (Commercial bentonite, GMZ24-200 bentonite, and GMZ-07 bentonite) in NaCl, Na₂SO₄, and CaCl₂ salt solutions. These three types of bentonite are representative materials planned for future nuclear waste disposal projects, making their experimental data both relevant and significant. Finally, this study suggests that the proposed fractal adsorption model is a practical tool for explaining the chemical effects on bentonite swelling at both macroscopic and microscopic levels.