Geosynthetic clay layer as surface sealing element of landfills

In Germany it is common to install two-element surface sealing systems on landfills containing non- and hazardous wastes. The elements applied are a geosynthetic clay layer (GCL) beneath and a geomembrane on top. The GCL consists of Na-bentonite clay, which is located between two needle-punched geotextiles. The thickness of the GCL is about 10 mm. The clay is dry when the GCL are installed, swelling occurs when the bentonite is hydrated. The swelling can lead to a thickness of the GCL which is up to the tenfold of the one in dry conditions. The swelling reduces the pore volume in be-tween the clay particles, in particular when swelling is restrained by the super-imposed load of the recultivation layer, which has to be installed instantaneously. The hydraulic conductivity is between 10e-11 and 10e-12 m/s. While the geomembrane is vulnerable to penetration damage, the GLC seals the spot of penetration due to the swelling effect. Consequently, the both sealing elements are compensational.
The GCL should be just applied in combination with a geomembrane as drying of a once swelled GLC leads to an increase of water conductivity. When installing only a recultivation layer on top, the depth should be 1.5 m as it leads commonly to homoge-nous water content in the deep soil zone. Deep rooting plants have to be eliminated as they may promote drying of the GCL. All GCL applied on German landfills need a certification by the German Working Group of the Federal States on Waste.