What is a Geosynthetics Clay Liner?

A geosynthetics clay liner (GCL) is a hydraulic barrier made of a thin layer of bentonite clay held between geotextiles, or bonded to a geomembrane. The layers are held together by needle punching, stitching or adhesive bonding.

GCLs are used mainly in waste management and containment, where environmental rules require leachate and other harmful liquids to be kept out of soil and groundwater. Compared with a compacted clay liner, a GCL is quick to install (it arrives in rolls rather than being built up in lifts), needs far less clay to be hauled to site, and seals small punctures as the bentonite swells.

Purpose of geosynthetics clay liner

A GCL is a containment barrier to water, leachate and other liquids, and often to gases. GCLs are used as replacements for compacted clay liners or geomembranes, or together with a geomembrane in a composite liner, where the GCL limits leakage through any holes in the membrane.

How is a geosynthetics clay liner made?

GCLs are factory-made rolls of a thin layer of bentonite clay sandwiched between two geotextiles, or bonded to a geomembrane. Needle punching, stitching or adhesive bonding holds the layers together and gives the liner shear strength on slopes.

Sodium bentonite swells when it takes on water and forms a low-permeability gel. A hydrated GCL typically has a hydraulic conductivity in the range of about 1×10⁻¹¹ to 5×10⁻¹¹ m/s. Index flux is tested to ASTM D5887 and swell index of the bentonite to ASTM D5890.

Installation of geosynthetics clay liner

Step 1: Survey the area to be lined. Excavate at least 12 inches (about 300 mm) below finished grade, so there is room for the soil cover that keeps the bentonite confined.
Step 2: Prepare the subgrade. Compact it and remove all rocks, roots and debris that could puncture the liner.
Step 3: Unroll the GCL, overlap adjacent panels as the manufacturer specifies (bentonite is often added along the overlap), and place the soil cover the same day so the liner does not hydrate unconfined.

How are geosynthetics clay liners applied in civil engineering?

GCLs provide a liquid or gas barrier wherever containment is needed: landfill lining and capping, reservoirs and canals, ornamental ponds, highway balancing reservoirs and retention ponds.

Few Geosynthetics Clay Liner Applications

Five of the most common uses:

Geosynthetics Clay Liners for Landfills

A badly lined landfill leaks leachate into the soil and groundwater around it for decades.

The base liner of a modern landfill is usually a composite: an HDPE geomembrane over a GCL or compacted clay. Geosynthetics clay liners for landfills are also used in the final cap, where they tolerate settlement of the waste better than compacted clay.

API Tanks & Foundation Liners

API is the American Petroleum Institute, which publishes standards for welded steel tanks that store oil, fuel and chemicals. API 650 (Annex I) covers release prevention barriers under the tank bottom: a low-permeability layer in the foundation that catches leaks from the floor plates and routes them to leak detection. A GCL, alone or with a geomembrane, is one way to build that layer.

Geosynthetics Clay Liners for Ponds

GCLs also hold clean water.

Some ponds have a natural clay bottom that holds water; many on sandy or fissured ground do not. A geosynthetics clay liner for ponds, covered with soil, gives a pond a natural-looking bed that retains water and supports plants and fish.

Earthen Spill Containment Berms

Earthen spill containment berms are bunded areas with earth walls, built in various sizes around high-risk equipment such as oil drums and tanks so that a spill stays inside the bund.

A GCL laid over the floor and walls of the berm and covered with soil makes the bund impermeable, so a spill is held at the surface instead of soaking into the ground.

Secondary Containment banks, Berms & Levees

Secondary containment catches what escapes if the primary container (a tank, pipe or pond liner) fails. GCLs suit these banks, berms and levees because they follow uneven ground and self-seal around small punctures.

Ocean Geosynthetics supplies GCLs, HDPE geomembranes and protection geotextiles for containment projects. For a worked example, see the GCL landfill leachate barrier case study.