Effect of swell pressure on GCL cover stability

This paper describes the importance of bentonite swell pressure on the stability of cover systems that incorporate a geosynthetic clay liner (GCL). The results of a one-dimensional swell test indicate that the field swell pressure of a needle-punched GCL ranges from 35 to 40 kPa An effective normal stress at or near this swell pressure may be required to maximize the contact area between the GCL and geomembrane and increase the static and seismic stability of a GCL cover. Since an effective normal stress of 35 to 40 kPa is probably not practical and a soil cover is usually not immediately placed, it is recommended that free swell conditions be assumed for GCL shear testing and the slope be designed using the resulting shear strength parameters. Suggestions for modifying existing products to increase GCL cover stability are also presented.