The Use of Geotextiles and Geosynthetic Clay Liners in Landfills

Report on the Use of Geotextiles and Geosynthetic Clay Liners in the Construction of Modern Landfills. Discuss a recent example.

Modern landfills are highly engineered containment systems that are designed to isolate surrounding soil and groundwater from the potentially harmful impacts of solid waste. Of particular concern is the segregation, collection and treatment of leachate, which consists of water and water-soluble compounds that accumulate as water percolates through solid waste.

In order to contain leachate, many modern landfills employ a composite liner system consisting of a geomembrane (or natural low permeability clay) overlying a compacted clay liner or geosynthetic clay liner (GCL). Geomembranes are relatively impervious polymer sheets (such as high-density polypropylene (HDPE) or polyvinyl chloride (PVC)) that slow the movement of leachate and permit its collection.

However, due to the angular nature of drainage gravel placed above the geomembrane and the large vertical stresses experienced due to dead weight and dynamic loads from earthmoving equipment, it is important to protect the geomembrane from puncture. This is achieved through the use of heavyweight geotextiles. Geotextiles are also used in modern landfills as a filter, preventing the movement of small soil and refuse particles into the leachate collection layer.

Underneath the geomembrane in many landfill systems is a secondary liner, consisting of either a geosynthetic clay liner (GCL) or compacted clay liner (CCL). Consisting of a thin layer of clay, typically sodium bentonite, sandwiched between two layers of a geotextile, GCL's are used as a hydraulic barrier to leachate movement. GCL's also have the advantage of being able to be used with a steeper slope than a CCL, allowing a greater waste storage volume.

A recent, local example of a modern landfill that employs a composite liner system is the Uleybury Landfill in Adelaide, South Australia (figure 1).

Figure 1: The Uleybury Landfill in South Australia is a modern landfill, situated in a disused quarry, that uses a composite liner system to protect the surrounding environment from leachate contamination [Source: personal photograph]

The Uleybury landfill uses a double composite liner system consisting of a HDPE geomembrane, protected by a geotextile layer, overlaying a geocomposite clay liner. Above the geomembrane is a drainage layer to ensure leachate is collected and treated (see figure 2).

Figure 2: The Uleybury Landfill utilises a double composite liner system to prevent the movement of leachate into the local groundwater [Source: Interpretative Sign photographed on site visit to Uleybury Landfill]

It is this liner system, combined with the baled waste operation, landfill gas management and future monitoring program that has lead to the Uleybury landfill being awarded the 2006 Case Earth Award.