Influence of Ca2+ concentration on hydraulic properties of bentonite-sand mixtures

A liner system containing clay or bentonite-sand mixtures is installed on the bottom of a landfill to prevent contaminants from flowing into the surrounding ground. The influence of Ca2+ concentration and local settlement on hydraulic properties of bentonite-sand mixtures is studied by model tests. It is shown that Ca2+ concentration has significant influence on the hydraulic properties, while the bentonite-sand mixtures leak with Ca2+ concentration more than 3.00g/L. Ca2+ concentration correlates with seepage time, which is shortened with the increase of Ca2+ concentration. Under the same settlement conditions, leakage occurs to the bentonite-sand mixtures infiltrated by Ca2+ ion solution but not to those by distilled water solution. When Ca2+ concentration is higher than two times Na+ in solution, the sodium bentonite converts to calcium bentonite, and the hydraulic properties of the bentonite-sand mixtures decrease. Therefore, it is of theoretical and practical values to investigate the influence of Ca2+ concentration and local settlement on hydraulic properties of the bentonite-sand mixtures.