Civil and Environmental Applications of Geosynthetics - Reinforced Soil Engineering: Advances in Research and Practice - page 12

clay. The problems may be alleviated through the use of white-surface
geomembranes and very flexible polyethylene (VFPE) geomembranes. New
geomembrane products are expected to overcome existing problems.
4.3 Geosynthetic Clay Liners as Hydraulic Barriers
Geosynthetic clay liners (GCLs) are proprietary products that are beginning to
replace geomembrane and clay liners. They are finding increased use in waste
containment systems (mostly landfill liners and covers) and reservoirs. GCLs
consist of very low-permeability bentonite or other clay materials supported by
geotextiles and/or geomembranes on one side or both. They are bonded together
by needling, stitching, or chemical adhesive (Fig. 7).
GCLs offer many advantages over conventional clay liners or
geomembrane-clay composite liners. GCLs are factory manufactured; thus the
quality is well controlled. Sodium bentonite is usually used in GCLs. The
permeability of bentonite is around 10 2 10 to 10 2 12 m/s, which is much lower
than native soils available in the field. While clay liners are typically from 30 cm
to 1 m thick, GCLs are approximately 5mm thick. This results in space saving in
a containment system. The installation of GCLs is rapid and simple. Unlike
geomembranes that require special welding equipment and skills, the seaming of
GCLs is provided by an overlapping length of about 15 cm. GCLs offer a self-
healing capability under puncture, as the availability of moisture typically leads
to swelling of bentonite.
Installation of CGLs is conducted under dry conditions. Hydration may
affect the properties of GCLs. It is also affected by the hydration liquid. Bentonite
Figure 7 Typical examples of geosynthetic clay liner.