Hydraulic performance of anionic polymer-treated bentonite-granular soil mixtures

In this study, hydraulic conductivity and viscosity determination tests were performed on two different bentonite-granular soil mixtures having various amounts of bentonite in order to obtain the optimum mixture to be used as a liner for waste containment facilities. To enhance the hydraulic capability of these mixtures, an anionic polymer was added to the bentonite. In bentonite-granular soil mixtures, two different aggregate compositions were used: A typical aggregate composition used in the production of C20 type concrete with a void ratio of 0.33 and an aggregate composition with a void ratio of 0.21 that was the minimum void ratio determined by testing various granular soil compositions. In these two mixtures, the bentonite content varied from 8 to 15% whereas the polymer content was within the range of 0.5-10% by mass. Test results indicated that intrinsic permeability decreased drastically due to an increase in the bentonite content. 15% bentonite addition caused a decrease of almost 5.5 orders of magnitude when compared with the granular soils without any bentonite content. 2% anionic polymer addition resulted in a decrease of approximately 2.5 orders of magnitude in hydraulic conductivity. However, further increase in polymer content had almost no effect on lowering hydraulic conductivity. 2% polymer addition in bentonite-granular soil mixtures provided hydraulic conductivity values as low as 10−11 m/s. The decrease in hydraulic conductivity was attributed to the increase in the viscosity of the fluid. Due to polymer addition, an inverse relationship existed between hydraulic conductivity and intrinsic permeability. As a result, polymer-treated bentonite-granular soil mixtures can effectively be used as barrier layers in waste containment facilities.