Geosynthetic clay liner and geomembrane are geosynthetic materials used in a variety of engineering and environmental applications. Although they have some similar anti-seepage properties. But they have obvious differences in composition, performance and application.
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BPM Geosynthetics is the leading geosynthetic clay liner and geomembrane manufacturer and supplier with 13+ years of Geosynthetic clay liner and HDPE geomembrane manufacturing experinces. In this article, we will discuss the differences of geosynthetic clay liners vs geomembranes. By comparing the differences between the two, we can make a better choice between a geosynthetic clay liner (GCL) and a geomembrane for your specific project.
Geosynthetic clay liner (GCL), also known as clay blanket, bentonite blankets, bentonite mats, prefabricated bentonite clay blankets and clay geosynthetic barriers, are factory-made hydraulic barriers consisting of a layer of bentonite or other composed of a very low permeability material supported by geotextiles and/or geomembranes that are mechanically fastened together by needling, stitching, or chemical adhesives. GCL liner is widely used in landfills to trap internal leakage. Its bentonite, consisting primarily (>70%) of montmorillonite or other expanded clays, is the preferred and most commonly used GCL. A typical GCL structure consists of two layers of geosynthetic material sewn together and surrounded by a layer of natural or processed Sodium bentonite. Typically, woven and/or nonwoven textile geosynthetics are used, however, polyethylene or geomembrane layers or geogrid geotextile materials have also been incorporated into the design or replaced the textile layer for added strength.
BPM geosynthetic clay liners are geosynthetic material specially used to prevent leakage in artificial lakes and waterscapes, landfills, underground garages, rooftop gardens, pools, oil depots and chemical storage yards. It is made of high-expansion Stable sodium bentonite is filled between a special composite geotextile and a non-woven fabric. The bentonite anti-seepage mat made by acupuncture can form many small fiber spaces. However, the bentonite particles cannot flow in one direction and will flow in one direction when exposed to water. A uniform and high-density gel-like waterproof layer is formed inside the pad to effectively prevent water leakage.
A geomembrane is an extremely low-permeability synthetic membrane liner or barrier that can be used with any geotechnical-related material to control fluid (liquid or gas) migration in man-made projects, structures or systems. Geomembranes are made from relatively thin, continuous polymer sheets, but they can also be made by impregnating geotextiles with asphalt, elastomers or polymer sprays, or as multi-layer asphalt geocomposites. Continuous polymer sheet geomembranes are by far the most common.
BPM Geosynthetics geomembrane is a waterproof barrier material produced from high-density polyethylene resin. The full name is “high-density polyethylene film”, which has excellent environmental stress cracking resistance, low temperature resistance, aging resistance, corrosion resistance, a large operating temperature range (-60–+60) and a long service life. It is widely used in domestic waste landfill anti-seepage, solid waste landfill anti-seepage, sewage treatment plant anti-seepage, artificial lake anti-seepage, tailings treatment and other anti-seepage projects.
Geosynthetic Clay Liner consists of a layer of bentonite encapsulated between two geotextiles or geocomposites. Bentonite is a natural clay with excellent swelling properties that provides high levels of water conductivity and chemical resistance.
Geomembranes are synthetic materials made from flexible polymer sheets. They are typically made from materials such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP) or polyvinyl chloride (PVC). BPM Geosynthetics geomembranes offer excellent impermeability and chemical resistance.
GCL waterproof blanket, Sodium Bentonite Geosynthetic Clay Line, is a new type of waterproof material. It is made of natural sodium bentonite, wrapped with two layers of geotextile, and reinforced with needle punching. Its anti-leakage mechanism is: the sodium-based particle bentonite selected for the bentonite waterproof blanket can expand more than 24 times when exposed to water, forming a uniform colloid system with high viscosity and low filter loss. Under the restriction of two layers of geotextile , causing the bentonite to expand from disorder to order. The result of continuous water absorption and expansion is to make the bentonite layer itself dense, thus having a waterproof effect. In order to facilitate construction and transportation, bentonite is locked between two layers of geosynthetic materials to protect and reinforce, giving the GCL waterproof blanket a certain overall tensile and puncture strength. GCL is primarily used as a barrier to prevent fluid migration in applications such as landfill covers, safety basins, and other hydraulic barriers. The bentonite in GCL swells on contact with water, creating a low-permeability barrier.
HDPE Geomembrane uses the impermeability of plastic films to block leakage channels in earth dams. It uses its large tensile strength and elongation to withstand water pressure and adapt to dam deformation. It aims to provide a highly impermeable barrier to prevent fluids ( including liquids and gases) migration. They are commonly used in applications such as landfill liners, ponds, reservoirs, mining facilities and other containment systems.
Geosynthetic Clay Liner (GCL) GCLs exhibit relatively low permeability due to the swelling properties of bentonite clay. The bentonite clay particles create a tortuous path for fluid flow, reducing hydraulic conductivity.
HDPE Geomembranes have very low permeability, providing an excellent barrier against fluid migration. They are engineered to have consistent and predictable permeability characteristics.
Geosynthetic clay liner is typically installed by unrolling them onto the prepared subgrade. The seams between adjacent GCL panels are often overlapped and mechanically or chemically bonded.
Geomembranes are installed by unrolling the sheets over the prepared subgrade and then seaming them together using various techniques such as heat welding, adhesive bonding, or fusion.
Geogrids consist of a regular open network of integrally connected, tensile elements (ribs), which may be linked by extrusion, bonding or interlacing. The apertures between the ribs are larger than the constituents. The ribs are made of polymeric materials such as high-density polyethylene (HDPE), polypropylene, or other durable polymers. The manufacturing process may involve stretching of the polymer material to orient the molecular structure, increasing strength and stiffness of the ribs.
The stiff ribs and strong junctions of a geogrid enable a high degree of interaction between the geogrid and the surrounding soil. Soil particles are able to partially penetrate into the apertures and become restrained by the ribs or confined within the apertures. Geogrids are ideal for stabilization or reinforcement of soils, with applications such as construction over weak soils, road foundations and earth retaining structures – as such, they are one of the most commonly used geosynthetics.
Tensar produces four types of geogrids: uniaxial geogrids, biaxial geogrids, multi-axial geogrids (TriAx®), and the more complex Tensar InterAx® geogrids. Visit Tensar’s geogrids page to learn more about them.
Geotextiles are the largest group of geosynthetics, as well as one of the earliest types to be created. They are permeable fabrics that consist of synthetic fibers such as polyester or polypropylene, and can be created as either woven, knitted or non-woven textiles. The non-woven types are manufactured from directionally or randomly oriented fibres/filaments mechanically or thermally/chemically bonded together. They can vary in strength and weight, from lightweight filter products to high strength reinforcement materials.
This category of geosynthetic, when used in association with soil, can provide a wide variety of functions including separation, filtration, drainage, protection and reinforcement. Although most commonly used as a separator before construction of roads, or as filter/separators in drainage applications, they can be used across a range of applications in engineering projects.
Geofoam, also known as EPS (Expanded Polystyrene), is an incredibly lightweight durable material that's can be used in numerous applications as an alternative to soil backfill. Geofoam blocks are created via polymeric expansion of the polystyrene, which produces many gas-filled, closed cells throughout the block. This design is what makes them so low in density.
The low density of geofoam makes it very useful on engineering projects as a fill material over soft or compressible foundation soils. Used as a lightweight core for an embankment, it will reduce settlements and may make it possible to avoid staged construction.
Geosynthetic clay liners (GCL) are built using two sheets of non-woven geotextile with a layer of sodium bentonite clay sandwiched between. The sheets are bonded together (using stitching or needle punching) to create structural integrity; they’re then heat treated to secure the layers in place.
GCL’s provide a faster, more convenient alternative to traditional clay lining of containment ponds. These materials have an added advantage in that the sodium bentonite layer has swelling properties. As such, clay liners offer a degree of self-sealing that reduces leakage. GCL liners benefit many geotechnical applications, including waste treatment and landfill.
Geocomposites combine of two or more of the geosynthetic types discussed above. Combining the features of each geosynthetic creates a product with more benefits than any individual product type, particularly useful in drainage and containment applications and some road foundation situations. For example, Tensar combines stabilization geogrids with separation/filtration geotextiles for use in road and rail foundations where fine soil migration may be an issue. Take a look at the Tensar FilterGrid product page for an example of a geocomposite.
Where geosynthetics are used to stabilize granular soils, this typically occurs via an interlocking mechanism. With geogrids, for example, the apertures between ribs allow aggregate to strike through and interlock, confining the aggregate material. Provided that the geogrid has strong junctions, and ribs that offer high stiffness at low strain, movement of the soil particles can be minimized, improving the mechanical behavior of the soil. This mechanical stabilization creates a composite layer that is stronger and more resistant to deformation.
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Geogrid stabilization is common in roadway foundations and in working platforms that will endure heavy loads, as it increases bearing capacity and reduces deformation under load. You can learn more about the stabilizing power of interlock in this Tensar article.
The drainage function of geosynthetics allows groundwater or other fluids, to be collected and pass through less permeable soils. Drainage geosynthetics can be used to dissipate pore pressure below embankments, intercept groundwater in slopes or behind structures, and provide edge drainage to road pavements.
Drainage geosynthetics are usually geocomposites, typically combining a geonet drainage core with one or more layers of geotextile. They are able to pass water (and other liquids or gas) through their structure to a collector or open space.
Good drainage is essential for roadways as water under the surface can lead to softening of subgrade soils and eventual loss of strength in the road structure. Therefore, geosynthetics can commonly be found in roads and railways, behind retaining walls, as well as below embankments where less permeable soils exist.
Erosion control is the practice of limiting damage to land due to the action of wind or water. Once the top layer of land is eroded, re-growth takes a long time, and this is where erosion control geosynthetics come in to give nature a helping hand.
Erosion control geosynthetics, typically, in the form of multi-layered mats, reduce soil erosion caused by impact of water droplets and surface runoff. They are rolled onto a surface and pegged in place. Some products combine synthetics with natural materials to provide enhanced moisture retention to encourage vegetation growth.
In areas where land is exposed to water flow or rainfall, erosion control geosynthetics are ideal for protecting the top layer of soil, encouraging vegetation to grow and preventing soil loss in the future. This is particularly common around areas of water and embankment slopes.
Soil particles, particularly finer particles, can be transported by water passing through soils. Filtration geosynthetics, usually geotextiles, are designed to retain soil particles on the upstream side of the filter, while allowing water to pass freely through. Even fine soil particles can be retained due to the ‘bridging’ effect of larger particles on the upstream side of the filter. Filtration is therefore most effective with one-directional water flow.
The filtration properties of geotextiles can be designed by varying the type and density of fibres, and the thickness and structure of the fabric. They are often combined with a drainage core in the form of a geocomposite. Suitably engineered products may be used to prevent soil migration into drainage aggregate layers or gravel filled drains, or for critical applications below riprap protection in river or coastal works.
To function as a separator, the geosynthetic must prevent soil with different particle size distributions from intermixing and causing the structural integrity to fail.
Separation is a required function in many applications, however it is vitally important to the layers of roads and pavements. Geotextile separators are routinely used below road and rail construction, in isolation or combined with a geogrid in the form of a geocomposite.
A geogrid can prevent expensive subbase material from punching into the soft subgrade. When a well-graded subbase is stabilized with a geogrid the geogrid/soil composite layer can prevent finer grained soil from migrating up into the subbase. When soil moisture levels are high, a geocomposite with geogrid and separator/filter properties may be used. Learn more in this blog article.
Geosynthetics are often applied in areas such as roadways, railways, airports and more.
For roads and runways, they’re primarily useful in stabilizing and separating unbound pavement layers. However, they can also be used to address issues with the underlying soil, or in providing side drainage.
Geogrids have been used to aid construction and enhance the performance of roads over soft ground since the s. More recent advancements have led to their increased use to enhance the service life of paved roads, reducing whole life costs. Visit this page on roads, pavements and surfaces to discover more on how Tensar products improve road construction projects.
Geosynthetics can be applied to solve a variety of problems below rail track. Stabilization geogrids are routinely used to increase the bearing capacity and stiffness of the trackbed over areas of weak soils. They can also be placed below the ballast layer to control lateral migration and deterioration of the ballast particles. Differential stiffness issues associated with transitions from rigid to flexible foundations can be addressed with geogrid stabilized transition zones. Visit this page on rail trackbed improvement to discover more on how Tensar products improve rail track maintenance and construction projects.
Geotextile separators and drainage geocomposites are used to control moisture related problems, while highly specialised sand filled geotextile mats can replace sand filters below trackbed.
The construction of earth embankments over weak soils presents challenges that can be addressed by the use of geosynthetics. Over-stressing of the foundation soil as construction proceeds can result in a deep rotational failure. The inclusion of geosynthetic reinforcement in the base of the embankment can maintain stability against this failure mechanism.
Three-dimensional cellular mattress systems, such as Stratum® Foundation Geocell, provide reinforcement at the base, but in addition, the inherent stiffness of the cellular mattress distributes load and influences the settlement profile. Geosynthetic wick drains, driven deep into the foundation soil can relieve excess pore pressure as the embankment rises, enabling more rapid construction.
Design and construction of a geogrid stabilized working platform for use with a ringer crane in the US was undertaken in and completed in . Problematic soil conditions were found at the crane pad area and consisted of fat clays and occasional sandy silt lenses and pockets. Stringent criteria for differential and total settlement needed to be met to ensure successful crane operation. Heavy seasonal rains were impacting construction.
A multi-axial geogrid-stabilized working platform was designed to improve allowable bearing capacity of the soil and to decrease potential settlement. The crane bearing pad was installed on time and on budget despite of numerous construction delays due to the heavy seasonal rains. Unlike the concrete option that was considered, the crushed stone could be easily removed and reused at other site locations. Estimated total cost savings of $3.1 Million when compared with original plans to construct a deep foundation system. Success of the geogrid stabilized platform was further demonstrated when it withstood Hurricane Harvey without damage and the crane was back in operation the day after the storm passed.
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The pavement section installation for the container storage area was underway. It was designed with two layers of a composite biaxial geogrid and geotextile fabric, with 12” ALDOT 825B aggregate placed on the bottom layer and 6” on the top layer. During construction, significant rutting and subgrade pumping occurred after installation of the first layer of geogrid and stone. There was significant risk in continuing to build the pavement section as designed due to the soft, unpredictable, and undocumented subgrade material.
Using Tensar+ design software, a Tensar representative designed a solution using NX850-FG to minimize cut and fill while also providing the separation benefits of a non-woven fabric. The design recommendation required a single 18” lift of coarse sand with low fines content to be placed on the NX850-FG. The original pavement section was then installed above the newly stabilized subgrade.
Download the full case study here.
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