Water retention characteristics of granular and powder bentonites

Geosynthetic Clay Liner (GCL) has become an important component of waste containment system. The GCL is laid at the as-rolled moisture condition in the field and hydrates through absorbing water from the underlying soils or compacted clay liner. The degree of hydration or saturation of the GCL is important as it can affect the performance of the GCL. Thus, the water retention curve (WRC) of GCL is important for understanding the saturation process of the GCL. The GCL consists of a layer of granular sodium bentonite clay sandwiched in between a nonwoven geotextile and a woven geotextile. Test results showed that the geotextiles are fully desaturated when the suction is greater than 2 kPa. Thus, the WRC of GCL over the larger suction range is governed by the bentonite. In this paper, the water retention of commercially available powder bentonite and granular bentonite used in the GCL are determined by direct measurement using tensiometer and indirect measurement using chilled-mirror hygrometer. The implications of the water retention characteristics of the bentonites in a GCL are discussed.