What is a Geosynthetic Clay Liner?
Geosynthetic clay liners (GCL) are special materials designed to prevent the free movement of liquids or fluids within the ground. That is, depending on the design, they can prevent water or leachate. In advanced designs, they can prevent gas movement.
Ideally, the GCL plays an important role when controlling pollution. A reason, some people refer to this Geosynthetic material as a hydraulic barrier.
Clay Geosynthetic Barrier Material
When choosing clay barriers, considering material with low permeability is critical. Such material will prevent possible leakages or seepage.
So far, Bentonite remains the material in the GCL manufacturing process. Bentonite is predominantly made from:
- Montmorillonite
- Expansive Clay
- Geosynthetic (these are mainly polymer materials)
Remember, the type of material directly influences the Geosynthetic clay liner cost. At the same time, even with these composite materials, the thickness is not that large.
At the same time, the material in the clay Geosynthetic barrier will affect its performance characteristics.
Development of GCL
The first GCL designs were made by Arthur Clem in 1962. In 1982, Arthur Clem filed the first patent for the modern Geosynthetic Clay Liners patent. By 1988, the GCL was playing a critical role in solid waste management. The United States Environmental Protection Agency was encouraging using the Geo-synthetic Clay Liners in most waste management in landfills.
Since then, many names have emerged referring to GCL products such as:
- Clay blankets
- Bentonite blankets
- Bentofix Geosynthetic clay liner
- Prefabricated bentonite clay blankets
- Bentonite mats
- Clay Geosynthetic barriers
Furthermore, other development such as the needle punching technique also improved the overall performance of the GCL.
Geosynthetic Vs. Compacted Clay Liners (CCL)
In most cases, there is always a question of whether you should choose CCL or GCL. Although these structures help to control pollution due to possible seepage or leakage, there are variables you must consider before installation.
And this leads us to an important comparison:
- Cost – GCL is more expensive than CCL
- Material – GCL has geomembrane or geotextile which is not the case in the compacted clay liners.
- Installation – installing GCL is easier than CCL. Moreover, CCLs are constructed on-site, while GCLs are manufactured in the factory.
- Thickness – compacted clay liners have an average thickness varying between 300 and 900 mm. On the other hand, GCL is about 6 mm.
- Hydraulic conductivity of clay – the CCL is 10−9 to 10−10 m/s on the other hand GCL is 10−10 to 10−12 m/s.
Geosynthetic Liner Advantages
Clay Geosynthetic barriers offer more advantages than the bottom liner covers. A reason most regulatory bodies are recommending the GCL.
The advantages include:
- Easy to install – the GCL is made in the factory. They come as a single piece of composite material that is easy to install. GCL has self-seaming property thereby you don’t need any special installation requirements.
- Low hydraulic conductivity – the degree of permeability is quite low. Therefore, it does not allow for any form of seepage.
- Self-repair capability – this reduces maintenance costs. In case of damage on Bentonite mats which may be due to swelling.
- Cost-effective – Where clay is not readily available clay Geosynthetic barriers offer a cost-effective solution.
- Thin structure allows for design flexibility – unlike the compacted clay lines (CCL) which are thin, the GCL is very thin. Therefore, a design with GCL will maximize the limited space available. On average, any hole that is 75 millimeters in diameter will seal itself. Of course, this is attributed to the extremely absorbent property of Bentonite.
- Compatible with HDPE – Therefore, you can use HDPE as a secondary liner during the installation process.
- Resistance to most Fluids – In addition to water, the GCL is resistant to most chemicals, and fuel oils. Besides, it will maintain its integrity during both dry and wet cycles.
In addition to these, the GCL is non-toxic, does not undergo aging reactions, and is durable. Using the GCL is an effective campaign for sustainable materials.
Clay Blankets Structure
Geosynthetic clay liner manufacturers combine different materials to make a robust structure that with very low permeability. Whichever the case, Bentonite forms a primary material in the GCL design. Besides, the Bentonite will also determine the Geosynthetic clay liner thickness.
In recent parts, other manufacturers have been testing some low permeability materials as a substitute.
Usually, the clay blankets structure may have either:
- Geotextile or,
- Geomembranes
Of course, during the GCL manufacturing process, these materials are stitched or bonded together using special adhesives. In between the two materials, you will find Bentonite.
Again, depending on the design of the Geosynthetic clay liner, you can choose those with woven or non-woven Geosynthetic. Remember, the structure will determine the clay blanket’s strength.
Ideally, the clay blanket’s structure will vary depending on the application. For instance, you will have either geomembrane or Geosynthetic with Bentonite. Of course, this is alongside an appropriate adhesive.
Furthermore, the Geosynthetic clay liner width will depend on the material size. Of course, the nature of the application and performance requirements will be key determinants here.
Still, when examining the clay blanket’s overall structure, it is worth mentioning that construction depends on the material sandwiching the Bentonite. That is;
- For structures with a geomembrane, you will use a special adhesive to bind the Bentonite material
- Structure with geotextile there are three options – stitch bonding, adhesive, or needle punching. Depending on the structural design, you can use one or three techniques.
Geosynthetic Clay Liner Manufacturing Process
Unlike compacted clay liners, Bentofix Geosynthetic clay liners are manufactured in the factory. They come as fully finished products ready for installation.
Usually, the Bentonite mats are prefabricated in the factory. Probably, this explains the reason they are at times called prefabricated Bentonite clay blankets.
Usually, the manufacturing process begins by choosing suitable Bentonite clay. Depending on the application, you can choose to use Geomembrane or Geotextile material.
Manufacturing these hydraulic barriers involve:
- Bonding or encapsulating Bentonite clay within layers of Geosynthetic materials
- Main techniques include stitch bonding or needle punching thereby producing unique structures
- The Geosynthetic layers can be one or more depending degree of hydraulic barrier required
Usually, the Geosynthetic material holds Bentonite clay for extremely low permeability.
Types of Clay Blankets
Types of Clay Blankets
There are many variables you can use to classify the GCL. For instance, you may consider Geosynthetic material, structure, and clay encapsulation technique.
However, it is worth mentioning that the main material in the GCL is Bentonite Clay. Therefore, our classification here will explore this critical component of the clay blankets.
Generally, you can consider:
- Nano-based Bentonite
- Calcium-based Bentonite
Let’s compare the two in the table below:
| Variable to Compare | Nano-based Bentonite | Calcium-based Bentonite |
| Expansion co-efficient | Low | High |
| Anti-seepage | Weak | Stronger |
| Application | Areas that require low waterproofing | Areas that require high waterproofing |
Prefabricated Bentonite Clay Blankets Quality Standards
Quality control is an important aspect when designing clay Geosynthetic barriers. For this reason, there are several Geosynthetic clay liner testing requirements established so far.
Remember, the fundamental aspects revolve around permeability, and durability, just to highlight a few. Here are the criteria for quality testing:
| Quality Standard (Testing Guideline) | Remarks |
| ASTM D5889 | · Quality control criteria for Geosynthetics including the Bentonite blankets |
| ASTM D5878 | · Focuses on the index flux for saturated Bentonite mats |
| ASTM D5890 | · Examines the swelling properties of the clay materials that form critical elements in GCL |
| ASTM D5891 | · Evaluates loss of fluid in the GCL’s clay component |
| ASTM D5993 | · Determines GCL’s mass per unit |
| ASTM D6243 | · Examines the shear strength in GCL |
| ASTM D-5084 | · Evaluating hydraulic conductivity |
Geosynthetic Clay Liner Applications
With environmental safety being a major concern Geosynthetic clay liner uses are becoming popular. Some common options include:
Making Landfills – By installing Bentonite mats, you will prevent possible seepage that could otherwise pollute the surrounding environment.
Hydraulic Barrier – Clay Geosynthetic barriers act as containment measures. That is, they will prevent liquids, such as water or leachate from seeping into the surrounding environment. Usually, this will prevent possible contamination or pollution.
Pools and Artificial Lakes – The GCL offers one of the best waterproofing properties. Usually, it is known for its anti-seepage properties. Therefore, your pools or lakes will not lose water.
Geosynthetic Clay Liner for Ponds – GCL helps in retaining water within the ponds. Therefore, no water will seep through the bottom of the pond. Once the GCL particles swell after water absorption, it offers the best water retention properties.
Underground Garage – It protects the garage from any seepage that may cause damage to items stored in the garage.
Roof Garden – Leakage from the roof garden may damage the roofing structure. The damage can be due to dampness. The GCL will ensure your roof structure remains dry.
Secondary Containment – GCL will not allow for any leakages due to the Bentonite clay which offers the best waterproofing properties.
Geosynthetic Clay Liner Installation Guidelines
First, it is important to note that installing Bentonite blankets is an easy and fast process. Again, the installation process is not as tedious as the compacted clay liners.
However, Bentonite blankets tend to be more delicate. Therefore, you must follow the GCL manufacturer guidelines for successful installation. Usually, this will prevent damaging the entire structure.
Remember, uncontrolled hydration during and after installation may cause swelling that may undermine the GCL performance. Under such circumstances, the Geotextile layers will begin to pull apart.
Although every GCL manufacturer will specify the installation process for their product, you should pay attention to the following critical aspects:
- Prepare subgrade and ensure the surface is smooth
- Carefully compact the site
- Ensure the surface is dry
- Between the adjoining sheets, there should be enough overlap
- Ensure the GCL is naturally relaxed besides, it must be attached firmly to the base layer
Note: If possible, only trained personnel should install the clay Geosynthetic barriers. Additionally, inspect the GCL for any possible defects. These may include possible holes or any other damage.
Remember, there is an approved Bentonite sealing powder. It is in the form of a paste that you can use to seal the damages.
Geosynthetic Clay Liner Specification and Properties
Before installing clay blankets, it is important to consider whether they meet the required criteria. Therefore, you need to understand the critical specification. They act as a guideline before undertaking any installation process:
· Geosynthetic Clay Liner Hydraulic Conductivity
Hydraulic conductivity is an important parameter when evaluating the ability to prevent possible seepage or leakage. Usually, this is an important factor before choosing this material for say landfill barrier application.
Currently, GCL technology offers low permeability both when dry and saturated. Of course, sodium Bentonite is responsible for the low Geosynthetic clay liner permeability. Usually, this is a unique clay from volcanic ash.
· Performance Properties/Characteristics
A clear knowledge of the structure and material will help you understand critical aspects of the GCL performance. For easier understanding, we shall evaluate the structure, material, and subsequent effect on the clay Geosynthetic barriers.
| GCL Configuration | Remarks |
| Geotextile + Bentonite +Stitch Bonding | · High resistance to shear forces |
| Non-woven Geotextile (On one side) + Bentonite + Needle Punching | · Exhibit exception resistance to interface friction
· Best design for slopes in landfills · Remember, non-woven Geotextile are more expensive than woven Geotextile |
| GCL with both stitch bonding and needle punching structure | · They are costly |
Disadvantages of Geosynthetic Clay Liner
Although GCL has many benefits, the only challenge when it comes to these systems is the initial costs. Depending on the structure, you may pay for a single unit.
For instance, GCL with non-woven Geotextile tends to be more expensive. However, when you compare the Geosynthetic clay liner lifespan it has long-term cost benefits.
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