Geosynthetic Clay Liner vs. Compacted Clay

Over the past decade or so, geosynthetic clay liners (GCLs) have replaced compacted clay liners in many applications, mainly because they give comparable or better hydraulic performance and are much easier to install. Ocean Geosynthetics prefabricated geosynthetic clay liners are used in landfill cover systems, composite liners, protection barriers, storage tanks, canal liners, pond liners and more.

What is a Geosynthetic Clay Liner?

A geosynthetic clay liner is a layer of sodium bentonite clay sandwiched between two geotextiles. The geotextiles are needle-punched, stitched or otherwise bonded together through the bentonite so the liner holds together and resists shear. They may be woven or non-woven geotextiles, depending on the project specification and application.

The geotextiles are usually polypropylene; the sealing layer is bentonite, a fine-grained, absorbent clay made mostly of the mineral montmorillonite, which swells when it gets wet. GCLs are used across geosynthetic sectors such as roadways, railways, waste treatment and landfills, gas and vapour barriers, ground engineering, agriculture, waterproofing and tunnelling.

What is unique about the Ocean Geosynthetics Prefabricated Geosynthetic Clay Liners?

Ocean Geosynthetics’ prefabricated GCLs consist of a bentonite layer encapsulated between two needle-punched geotextiles, which are then heat-treated under controlled conditions to thermally lock the fibres in place. Locking the fibres raises the internal shear strength, which matters on slopes. They are used as single liners or as part of a composite liner with a geomembrane.

The benefits of geosynthetic clay liners over compacted clay

Here are the main reasons GCLs are replacing traditional compacted clay.

Low permeability in a thin layer: a hydrated GCL typically has a hydraulic conductivity of around 1 x 10^-11 to 5 x 10^-11 m/s, lower than the 1 x 10^-9 m/s usually specified for a compacted clay liner, in a layer under 10 mm thick instead of 600 mm or more of compacted clay. Bentonite quality is checked by swell index (ASTM D5890), and the finished GCL by index flux (ASTM D5887).

Natural sealant: sodium bentonite has a strong affinity for water and swells when wet, so it seals around pipe penetrations, self-heals small punctures and seals itself at overlaps.

Long-term performance: GCLs tolerate differential settlement better than compacted clay and are less affected by wet-dry cycles, because hydrated sodium bentonite is highly plastic and can swell back into small cracks. Compacted clay liners can crack under the same conditions, and their performance depends heavily on achieving the right moisture content, clay content and density in the field, which in turn depends on the weather during construction. GCLs are made under factory control, so their properties are more consistent. They are not immune to everything: the bentonite must be hydrated with fresh water before it meets strong leachate, and calcium-rich soils or saline water can reduce its swelling, so GCLs are normally covered and often used under a geomembrane.

Ease of Construction and Installation: GCLs need less effort to install, use fewer natural resources and, in landfills, take up much less airspace than a thick clay layer. Installation is a matter of unrolling and overlapping the panels, instead of hauling, dumping, spreading and compacting clay, which adds construction time, logistics and cost. Compacted clay liners depend on local borrow material; GCLs are made in a factory, where raw materials and finished product are tested during and after production.

Choose Ocean Geosynthetics for the complete range of prefabricated geosynthetic clay liners.

Ocean Geosynthetics prefabricated geosynthetic clay liners self-heal and self-seam, cope better with wet-dry and freeze-thaw cycles than compacted clay, and are cost-efficient to install. To compare GCLs with the rest of our range, see our geosynthetics products and materials.