Determining the hydraulic conductivity and swelling behaviors of attapulgite enhanced geosynthetic clay liners with salt solutions

This study covers the basic characteristics, swelling indices and hydraulic conductivities of geosynthetic clay liners (GCLs) which were produced with attapulgite-polymer bentonite mixtures (0, 30, 50, and 70 percent of attapulgite) under a research project. It is observed that as the amount of attapulgite in the GCL increased, the liquid limit, plasticity index, fine-clay content, and cation exchange capacity of GCLs decreased. Swell indices in deionized water (DIW) decreased from 21 mL/2g (Polymer Bentonite-PB) to 6 mL/2g (attapulgite), whereas it slightly reduced in salt solutions (10 mL/2g to 6 mL/2g). In the hydraulic conductivity tests, DIW, 100 mM KCl, 50, 100 and 500 mM CaCl2, 50 mM MgCl2 and 50 mM CuCl2 solutions were used as the permeant. The tests with DIW, the hydraulic conductivities of non-prehydrated GCLs up to 50 percent attapulgite content slightly increased from 5.8×10-11 m/s (PB GCL) to 1.2×10-10 m/s (50%PB+50%A) and those of prehydrated GCLs increased from 3.2×10-11 m/s to 2.0×10-11 m/s. However, when attapulgite content in GCL increased to 70 percent, then hydraulic conductivity remarkably increased to 8.7×10-7 and 1.3×10-8 m/s for non-prehydrated and prehydrated GCLs, respectively (i.e. 30%PB+70%A). Accordingly, as the cell pressure increased gradually from 35 to 280 kPa, the hydraulic conductivities gradually decreased. Regardless of solution type and concentration, the hydraulic conductivities obtained with salt solutions were found to be 3-4 orders of magnitude greater than those obtained with DIW. The only exception is the tests conucted with 50 mM CuCl2 solutions. With this solution, the hydraulic conductivities were low (10-11 - 10-12 m/s). All permability and swell indices were evaluated together and found to be partially compatible with the relationship previously given in the literature. Although the final water content of GCLs increased with the amount of attapulgite, no relationship was established with hydraulic conductivity. Similarly, there is no correlation between the final water contents and the hydraulic conductivities.