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In construction, preventing the penetration of liquids and gases is essential to maintaining the integrity of a structure. Often, containment is just as important especially when dealing with chemical contaminants or other waste. When looking to stop the spread of contaminated liquids and gases, there are few tools as effective as geosynthetic clay liners (GCL). Read on to learn how to design barriers to liquids and gases using three types of GCL: single liners, composite liners, and composite covers.
How do you use GCL as a single liner?
A single lining, used alone with no composite or back-up geomembranes (1), is the simplest application of geosynthetic clay liners. Even this simple application has two practical uses: as a liner for canals, and as means to line underground storage tanks.
Underground storage tanks often necessitate a secondary containment liner for environmental safety in cases of failure. With a single liner GCL, you can contain the spread of liquid in the storage tank in the event of a tank burst or pipe leak. A geomembrane could also be used for this task, but GCLs have the advantage of very low permeability and are self-repairing to a degree in most situations. However, one potential area of failure can come from the choice of soil cover.
When using GCL as a single liner, it is good to keep in mind the choice of material. For example, gravel is often used to cover the area surrounding underground tanks. The mineralogy of gravel can greatly affect the integrity of the GCL. Limestone, for instance, will leach calcium and magnesium down to the GCL from rainwater infiltration. This may cause cation exchange that weakens the chemical composition of the liner. Designing a good surface seal over the unground tank and GCL barrier is one approach toward minimizing this effect.
How do you use GCL as a composite liner?
Although GCLs used as a single liner can be powerful, there are many more applications for GCL when used as a composite.
Multiple geosynthetics can be combined to tackle unique applications or as a way to augment some GCL traits. For example, the durability and low permeability properties of GCLs can be augmented by overlaying a geomembrane (GM) onto a sheet of GCL. This composite liner is useful for landfills and surface impoundments.
This composite liner’s improved durability and reliability allows it to be used as the primary liner of double-lined landfill facilities. Just how powerful is the GM/GCL composite versus pure GM or GM/compacted clay liner (CCL) as a liner? GM/GCL is able to greatly outperform the other approaches especially when it comes to the reduction of leakage rates.
When using GM alone, even the smallest hole brings leachate directly into the leak detection system with sufficient driving hydraulic head. The high swelling characteristics of the bentonite clay component in the GCL will work to seal the leak in the GM. However, owners, engineers, and regulators need to be aware consolidation water from a GCL can be of detectable quantity and confused as leakage as the landfill cell is filled. Chemical analysis of the recovered fluids should be performed to determine if leachate parameters are present, thus a means of differentiating between consolidation water and actual leakage.
How do you use GCL as a composite cover?
Agru GeoClay® is a reinforced needle-punched geosynthetic clay liner that serves as a primary or secondary containment in composite landfill closures, mining leach pads, tailing impoundments and reclamations, and pools and lagoons. Its defining features include a self-healing and self-sealing design, efficient installation, and improved barrier design.
The material comprises a uniform layer of granular bentonite encapsulated between two nonwoven geotextiles and is ideal for moderate to steep slopes and moderate to high loads. Available in roll widths of up to 15.5’, Agru GeoClay is hydraulically superior to several feet of compacted clay. This means that Agru GeoClay can be installed with increased efficiently, thereby reducing the projects’s carbon footprint. For example, a single truckload of GeoClay can cover 3/4 of an acre.
- Koerner, Robert M. “Designing with Geosynthetics – 6Th Edition.” Vol2. Xlibris US. Kindle Edition. (2012-01-16).
- GRI-GCL3 Specification. Geosynthetic Institute. (2016). http://www.geosynthetic-institute.org/grispecs/gcl3.pdf.