Geomembrane

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A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid 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.

Contents

Manufacturing

The manufacturing of geomembranes begins with the production of the raw materials, which include the polymer resin, and various additives such as antioxidants, plasticizers, fillers, carbon black, and lubricants (as a processing aid). These raw materials (i.e., the "formulation") are then processed into sheets of various widths and thickness by extrusion, calendering, and/or spread coating.

Three methods used to manufacture geomembranes Three methods used to manufacture geomembranes.jpg
Three methods used to manufacture geomembranes

A 2010 estimate cited geomembranes as the largest geosynthetic material in dollar terms at US$1.8 billion per year worldwide, which is 35% of the market. [2] The US market is currently divided between HDPE, LLDPE, fPP, PVC, CSPE-R, EPDM-R and others (such as EIA-R and BGMs), and can be summarized as follows:[ citation needed ] (Note that M m2 refers to millions of square meters.)

The above represents approximately $1.8 billion in worldwide sales. Projections for future geomembrane usage are strongly dependent on the application and geographical location. Landfill liners and covers in North America and Europe will probably see modest growth (~ 5%), while in other parts of the world growth could be dramatic (10–15%).[ citation needed ] Perhaps the greatest increases will be seen in the containment of coal ash and heap leach mining for precious metal capture.

Properties

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 method 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:

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.

Endurance

Any phenomenon that causes polymeric chain scission, bond breaking, additive depletion, or extraction within the geomembrane must be considered as compromising to its long-term performance. There are a number of potential concerns in this regard. While each is material-specific, the general behavior trend is to cause the geomembrane to become brittle in its stress-strain behavior over time. There are several mechanical properties to track in monitoring such long term degradation: the decrease in elongation at failure, the increase in modulus of elasticity, the increase (then decrease) in stress at failure (i.e., strength), and the general loss of ductility. Obviously, many of the physical and mechanical properties could be used to monitor the polymeric degradation process.

Lifetime

Geomembranes degrade slowly enough that their lifetime behavior is as yet uncharted. Thus, accelerated testing, either by high stress, elevated temperatures and/or aggressive liquids, is the only way to determine how the material will behave long-term. Lifetime prediction methods use the following means of interpreting the data:

Seaming

The fundamental mechanism of seaming polymeric geomembrane sheets together is to temporarily reorganize the polymer structure (by melting or softening) of the two opposing surfaces to be joined in a controlled manner that, after the application of pressure, results in the two sheets being bonded together. This reorganization results from an input of energy that originates from either thermal or chemical processes. These processes may involve the addition of additional polymer in the area to be bonded.

Ideally, seaming two geomembrane sheets should result in no net loss of tensile strength across the two sheets, and the joined sheets should perform as one single geomembrane sheet. However, due to stress concentrations resulting from the seam geometry, current seaming techniques may result in minor tensile strength and/or elongation loss relative to the parent sheet. The characteristics of the seamed area are a function of the type of geomembrane and the seaming technique used.


Applications

Geomembrane installation as part of the construction of a base liner system of a landfill Geomembrane installation.jpg
Geomembrane installation as part of the construction of a base liner system of a landfill

Geomembranes have been used in the following environmental, geotechnical, hydraulic, transportation, and private development applications:

See also

Related Research Articles

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<span class="mw-page-title-main">High-density polyethylene</span> Class of polyethylenes

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<span class="mw-page-title-main">Waterproofing</span> Process of making an object or structure waterproof or water-resistant

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<span class="mw-page-title-main">Geotextile</span> Textile material used in ground stabilization and construction

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<span class="mw-page-title-main">Pond liner</span>

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<span class="mw-page-title-main">Geocomposite</span> Materials to improve technical properties of soil or geotechnical structure

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<span class="mw-page-title-main">Cellular confinement</span> Confinement system used in construction and geotechnical engineering

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A geonet is a geosynthetic material similar in structure to a geogrid, consisting of integrally connected parallel sets of ribs overlying similar sets at various angles for in-plane drainage of liquids or gases. Geonets are often laminated with geotextiles on one or both surfaces and are then referred to as drainage geocomposites. They are competitive with other drainage geocomposites having different core configurations.

Final cover is a multilayered system of various materials which are primarily used to reduce the amount of storm water that will enter a landfill after closing. Proper final cover systems will also minimize the surface water on the liner system, resist erosion due to wind or runoff, control the migrations of landfill gases, and improve aesthetics.

Novel polymeric alloy (NPA) is a polymeric alloy composed of polyolefin and thermoplastic engineering polymer with enhanced engineering properties. NPA was developed for use in geosynthetics. One of the first commercial NPA applications was in the manufacturer of polymeric strips used to form Neoloy® cellular confinement systems (geocells).

Electrical liner integrity surveys, also known as leak location surveys are a post-installation quality control method of detecting leaks in geomembranes. Geomembranes are typically used for large-scale containment of liquid or solid waste. These electrical survey techniques are widely embraced as the state-of-the-art methods of locating leaks in installed geomembranes, which is imperative for the long-term protection of groundwater and the maintenance of water resources. Increasingly specified by environmental regulations, the methods are also applied voluntarily by many site owners as responsible environmental stewards and to minimize future liability.

<span class="mw-page-title-main">Fabricated geomembranes</span>

Geomembranes are thin plastic sheets that are essentially impervious and are used to prevent leakage from liquid or solid-storage facilities. Geomembranes are frequently referred to as Flexible Membrane Liners (FMLs) in environmental regulations, such as in Subtitle D of the Resource Conservation and Recovery Act.

Ronald Kerry Rowe, OC, BSc, BE, PhD, D.Eng, DSc (hc), FRS, FREng, NAE, FRSC, FCAE, Dist.M.ASCE, FEIC, FIE(Aust), FCSCE, PEng., CPEng. is a Canadian civil engineer of Australian birth, one of the pioneers of geosynthetics.

<span class="mw-page-title-main">Jean-Pierre Giroud</span>

Jean-Pierre Giroud is a French geotechnical engineer and a pioneer of geosynthetics since 1970. In 1977, he coined the words "geotextile" and "geomembrane", thus initiating the "geo-terminology". He is also a past president of the International Geosynthetics Society, member of the US National Academies, and Chevalier de la Légion d'Honneur.

<span class="mw-page-title-main">Bituminous geomembrane</span> Type of geomembrane

Bituminous geomembrane (BGM) is a type of geomembrane consisting of a reinforcing geotextile to provide mechanical strength and elastomeric bitumen to provide impermeability. Other components such as sand, a glass fleece, and/or a polyester film can be incorporated into the layers of a BGM. Bituminous geomembranes are differentiated from bituminous waterproofing materials used in buildings due in part to their wide roll width, which can exceed 5m, and their substantial thickness of up to 6.0mm.

References

  1. 1 2 Koerner, R. M. (2012). Designing With Geosynthetics (6th ed.). Xlibris Publishing Co., 914 pgs.
  2. 1 2 Müller, W. W.; Saathoff, F. (2015). "Geosynthetics in geoenvironmental engineering". Science and Technology of Advanced Materials. 16 (3): 034605. Bibcode:2015STAdM..16c4605M. doi:10.1088/1468-6996/16/3/034605. PMC   5099829 . PMID   27877792.

Further reading

  1. ICOLD Bulletin 135, Geomembrane Sealing Systems for Dams, 2010, Paris, France, 464 pgs.
  2. August, H., Holzlöhne, U. and Meggys, T. (1997), Advanced Landfill Liner Systems, Thomas Telford Publ., London, 389 pgs.
  3. Kays, W. B. (1987), Construction of Linings for Reservoirs, Tanks and Pollution Control Foundation, J. Wiley and Sons, New York, NY, 379 pgs.
  4. Rollin, A. and Rigo, J. M. (1991), Geomembranes: Identification and Performance Testing, Chapman and Hall Publ., London, 355 pgs.
  5. Müller, W. (2007), HDPE Geomembranes in Geotechnics, Springer-Verlag Publ., Berlin, 485 pgs.
  6. Sharma, H. D. and Lewis, S. P. (1994), Waste Containment Systems, Waste Stabilization and Landfills, J. Wiley and Sons, New York, NY, 586 pgs.