Swelling characteristics of needlepunched, thermally treated geosynthetic clay liners

The swelling characteristics of five different geosynthetic clay liners (GC Ls) are examined. Results show that two thermally treated GCLs have similar swell properties but a third thermally treated GCL with bentonite impregna ted in the cover geotextile swells to higher GCL bulk void ratios at stress es below 100 kPa. This is attributed to the unconfined swelling of the bent onite present on the surface of the cover geotextile. A thermally treated n eedlepunched GCL is shown to have an equilibrium swell height that is 50% s maller than that of a non thermally treated needlepunched GCL at 6 kPa. Mic roscopic examination of the thermal and non-thermally treated fibres before and after the 6 kPa swell tests shows that more thermally treated fibres r emain 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 f or pullout of the fibres decreases. Diffusion tests performed on a thermall y treated needlepunched GCL and non-thermally treated needlepunched GCL und er free swell conditions show that the diffusion coefficients for Na+ and C l- are lower for the thermally treated, needlepunched GCL than for the non- thermally treated GCL under otherwise similar conditions because of the hig her bulk void ratio of the latter GCL. (C) 2000 Elsevier Science Ltd. All r ights reserved.