A geomembrane is a very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (or gas) migration in a human-made project, structure, or system. Geomembranes are made from relatively thin continuous polymeric sheets, but they can also be made from the impregnation of geotextiles with asphalt, elastomer or polymer sprays, or as multilayered bitumen geocomposites. Continuous polymer sheet geomembranes are, by far, the most common.
Properties of Geomembrane
The majority of generic geomembrane test methods that are referenced worldwide are by the ASTM International|American Society of Testing and Materials (ASTM) due to their long history in this activity. More recent are test methods developed by the International Organization for Standardization (ISO). Lastly, the Geosynthetic Research Institute (GRI) has developed test methods that are only for test methods not addressed by ASTM or ISO. Of course, individual countries and manufacturers often have specific (and sometimes) proprietary test methods.
Physical properties
The main physical properties of geomembranes in the as-manufactured state are:
- Thickness (smooth sheet, textured, asperity height)
- Density
- Melt flow index
- Mass per unit area (weight)
Mechanical properties
There are a number of mechanical tests that have been developed to determine the strength of polymeric sheet materials. Many have been adopted for use in evaluating geomembranes. They represent both quality control and design, i.e., index versus performance tests.
- Tensile strength and elongation (index, wide width, axisymmetric, and seams)
- Tear resistance
- Impact resistance
- Puncture resistance
- interface shear strength
- Anchorage strength
- Stress cracking (constant load and single point).
Geomembrane for multiple project applications
Geomembrane for landfill
Geomembranes are ideal for use in landfill caps, landfill covers, landfill liners, temporary landfill closures and more, due to their ability to effortlessly accommodate differential settlement in the waste pile. Its high elongation and durability make PVC the best environmental liner for these applications. First utilized as bottom liners for municipal waste containment and landfill closures to inhibit rainwater leakage,
Geomembrane is an ideal geomembrane cover material for applications in:
- Municipal solid waste (MSW), and yard waste (in several states) landfill disposal facilities
- Low-hazard industrial waste, C&D construction and demolition waste debris, other nonhazardous industrial waste landfill disposal facilities
- Coal ash basin closure
- Facilities that accept fly ash, cement kiln ash, wood ash, lime kiln dust, and foundry sands
Geomembrane for caps and closures
Permanent geomembrane caps are subjected to a great deal of strain in all directions due to differential settlement and occasional gas pressure buildup from beneath. Caps are often placed on sloped areas and expected to hold a veneer of other geosynthetics and soil above them over a long period. Geomembrane covers are generally used to protect materials from water infiltration and to prevent loss of material from erosion by wind or water. Additionally, covers can provide odor control.
Short-term cover applications include soil remediation projects, temporary stockpile covers and erosion protection on slopes in active construction sites. Long-term applications include landfill closure covers or caps. Another application is to extend the life of above-ground storage tank roofs.
Geomembrane for pond liner
Pond liners offer a host of advantages as a pond liner, not all are equal. Even liners of the same material can show significant differences in performance. Setting test methods, standards of practice, and product specifications for the manufacturing, design, and installation of geosynthetics like HDPE liner are among the purviews of the Geosynthetic Institute (GSI).
Pond liners are both tough and flexible, with high resistance to chemicals and corrosion. They are among the most durable and long-lasting polyethylene liners on the market. They can be fusion weld together, forming permanent seals in the field. The fusion welding aspect requires an experienced welder and related equipment to ensure a quality installation. Pond liners are safe for both fish and plants. Overall liners are very cost-effective and have among the highest service lifespan of all polyethylene liners.
Geomembrane for mining
In this application, the HDPE geomembrane liner serves as a barrier for separation and is also the most important component in heap leaching. The geomembrane must resist chemical attack, point loads from typically high heap loading conditions, site-specific topography, site-specific climate conditions, and site-specific construction conditions. GCL is a cost-effective alternative for a composite liner system, especially if on-site sources of clay are insufficient. GCL comprises a bentonite (water absorbing mineral) layer between two nonwoven geotextile layers. A 10 mm thick GCL will typically perform similarly or better than a 30 cm CCL and even demonstrate self-healing capabilities. GCL also provides additional filtration and barrier capabilities. The protection layer is made with a nonwoven geotextile and helps distribute loads and provide reinforcement for the underlying geomembrane. The protection layer also assists with filtration and drainage, by preventing small particles and gravel from reaching the geomembrane.
Geomembrane for secondary containment
From small tanks to entire tank farms, the secondary containment area is a critical component of tank lining protection. Geomembranes have been proven to perform in hundreds of secondary containment applications. For exposed applications. Conductive geomembrane can be used to detect post-installation damage and as part of a periodic maintenance program. Geomembranes are used extensively in secondary containment applications, such as for spill protection with chemical storage tanks. Geomembranes are made by combining one or more thermoplastic polymers with additives, like plasticizers, carbon black, processing aids, anti-oxidants. A wide range of thermoplastics resins are used for geomembranes, including high density polyethylene (HDPE), very low density polyethylene geomembrane (VLDPE), polyvinyl chloride (PVC), polypropylene (PP).
When selecting the type of secondary containment to use, one must consider the geomembrane’s compatibility with the type of substance or waste to be contained, its durability, and its resistance to fire, heat and sunlight. Therefore, mechanical properties (such as tensile behaviour and tear resistance) and durability properties (e.g., heat resistance) are properties of the geomembranes that should be examined to determine the most appropriate material in relation to the final use. The tensile properties refer to the tensile strength of a geomembrane and the ability of the material to elongate under stress. These properties must be sufficient to satisfy the stresses (for example self-weight) and the strains (for example, not exceeding the yield strain for HDPE) anticipated during its service life.
Geomembrane for canal liners
Geomembranes are commonly used to control seepage from water canals. There are many types of geomembranes available for this application including PVC, HDPE, LDPE, CSPE, and EPDM geomembranes. Frequently these geomembranes require protection and there are several protection options including compacted soil, concrete, or shotcrete. The U.S. Bureau of Reclamation (USBR) has conducted a number of test programs on canal-lining systems including the Deschutes Canal-Lining Demonstration Project which involves the performance of 34 canal test-sections, many of which utilize geomembranes. Based on USBR and other test programs this paper examines the effectiveness of different types of geomembrane-based canal lining systems in terms of cost, seepage/leakage reduction, and long term durability.
Geomembranes for oil & gas containment
HDPE textured geomembrane is designed and fabricated with either a single-sided or double-sided textured surface which is made by automatic production liner and optimized engineered processes. BPM HDPE textured geomembrane is made of finest quality imported high density polyethylene (HDPE) raw materials professional production process and technology. BPM textured geomembrane liner products are packed in double woven geotextile and strength belts. HDPE textured geomembrane liner has the rough surface on one or both sides which can highly improve the friction coefficient which fits more suitable for steep slope and vertical engineering design work which maximize the effective volume of geomembrane to increased frictional resistance and other chemical and physical properties as smooth HDPE geomembrane. High-density polyethylene textured geomembrane exhibits superior shear strength and the highest multi-axial performance which features superior high shear strength, big friction angles, outstanding elongation and highest interface surface friction coefficient.
Conclusion
Geomembranes are being used in environmental, hydraulic, transportation, and oil and gas applications as well as the waste industry. The most common type are the continuous polymeric sheets. When larger geomembranes are needed, they are thermally or chemically melted together at the seams for strength and durability.