Geosynthetic clay liners (GCLs) are sealing elements, which contain natural sodium bentonite encapsulated between geotextile components. They are used in a variety of sealing applications and are most commonly employed to replace compacted clay liners (CCLs). One important field of application is landfill capping systems. In that geochemical environment an ion exchange of sodium-bentonite to calcium -bentonite occurs over a period of approximately 1-3 years, if in contact with cover-soil seepage. As a result, there is a slight increase in hydraulic conductivity of approximately half to one order of magnitude. This is, however, not alarming, as long as the design engineers take this effect into consideration. Landfill capping systems are characterized by unsaturated conditions, as often found in applications with low confining stress (< 15 kN/m(2), less than 0.75 m soil-cover). In such cases, GCLs tend to show desiccation cracks, which cause a significant increase of the permeability. In contrast to CCLs, where self scaling is unlikely to occur under low confining stress, a self-sealing of calcium-bentonite GCls takes place by swelling and plastification of bentonite, if a soil-cover of more than 0.75 in (confining stress > 15 kN/m(2)) is provided. (C) 2001 Elsevier Science Ltd. All rights reserved.
