Swelling characteristics of needlepunched, thermally treated geosynthetic clay liners

The swelling characteristics of five different geosynthetic clay liners (GCLs) are examined. Results show that two thermally treated GCLs have similar swell properties but a third thermally treated GCL with bentonite impregnated in the cover geotextile swells to higher GCL bulk void ratios at stresses below 100 kPa. This is attributed to the unconfined swelling of the bentonite present on the surface of the cover geotextile. A thermally treated needlepunched GCL is shown to have an equilibrium swell height that is 50% smaller than that of a non thermally treated needlepunched GCL at 6 kPa. Microscopic examination of the thermal and non-thermally treated fibres before and after the 6 kPa swell tests shows that more thermally treated fibres remain visible on the bottom of the geotextile compared to the non-thermally treated fibres. Additional swell tests at 20 kPa and 100 kPa suggest that as the confining stress increases on a GCL during hydration, the tendency for pullout of the fibres decreases. Diffusion tests performed on a thermally treated needlepunched GCL and non-thermally treated needlepunched GCL under free swell conditions show that the diffusion coefficients for Na+ and Cl- are lower for the thermally treated, needlepunched GCL than for the non-thermally treated GCL under otherwise similar conditions because of the higher bulk void ratio of the latter GCL. (C) 2000 Elsevier Science Ltd. All rights reserved.