Geomembrane

Last updated November 02, 2023

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.

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.

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.)

high-density polyethylene (HDPE) ~ 35% or 105 M m²
linear low-density polyethylene (LLDPE) ~ 25% or 75 M m²
polyvinyl chloride (PVC) ~ 25% or 75 M m²
flexible polypropylene (fPP) ~ 10% or 30 M m²
chlorosulfonated polyethylene (CSPE) ~ 2% or 6 M m²
ethylene propylene diene terpolymer (EPDM) ~ 3% or 9 M m²

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:

Thickness (smooth sheet, textured, asperity height)
Density
Melt flow index
Mass per unit area (weight)
Vapor transmission (water and solvent).

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).

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.

ultraviolet light exposure (laboratory of field)
radioactive degradation
biological degradation (animals, fungi or bacteria)
chemical degradation
thermal behavior (hot or cold)
oxidative degradation.

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:

Stress limit testing: A method by the HDPE pipe industry in the United States for determining the value of hydrostatic design basis stress.
Rate process method: Used in Europe for pipes and geomembranes, the method yields similar results as stress limit testing.
Hoechst multiparameter approach: A method that utilizes biaxial stresses and stress relaxation for lifetime prediction and can include seams as well.
Arrhenius modeling: A method for testing geomembranes (and other geosynthetics) described in Koerner for both buried and exposed conditions.^[1]^{[ self-published source ]}

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

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

As liners for potable water
As liners for reserve water (e.g., safe shutdown of nuclear facilities)
As liners for waste liquids (e.g., sewage sludge)
Liners for radioactive or hazardous waste liquid
As liners for secondary containment of underground storage tanks
As liners for solar ponds
As liners for brine solutions
As liners for the agriculture industry
As liners for the aquiculture industry, such as fish/shrimp pond
As liners for golf course water holes and sand bunkers
As liners for all types of decorative and architectural ponds
As liners for water conveyance canals
As liners for various waste conveyance canals
As liners for primary, secondary, and/or tertiary solid-waste landfills and waste piles
As liners for heap leach pads
As covers (caps) for solid-waste landfills
As covers for aerobic and anaerobic manure digesters in the agriculture industry
As covers for power plant coal ash
As liners for vertical walls: single or double with leak detection
As cutoffs within zoned earth dams for seepage control
As linings for emergency spillways
As waterproofing liners within tunnels and pipelines
As waterproof facing of earth and rockfill dams
As waterproof facing for roller compacted concrete dams
As waterproof facing for masonry and concrete dams
Within cofferdams for seepage control
As floating reservoirs for seepage control
As floating reservoir covers for preventing pollution
To contain and transport liquids in trucks
To contain and transport potable water and other liquids in the ocean
As a barrier to odors from landfills
As a barrier to vapors (radon, hydrocarbons, etc.) beneath buildings
To control expansive soils
To control frost-susceptible soils
To shield sinkhole-susceptible areas from flowing water
To prevent infiltration of water in sensitive areas
To form barrier tubes as dams
To face structural supports as temporary cofferdams
To conduct water flow into preferred paths
Beneath highways to prevent pollution from deicing salts
Beneath and adjacent to highways to capture hazardous liquid spills
As containment structures for temporary surcharges
To aid in establishing uniformity of subsurface compressibility and subsidence
Beneath asphalt overlays as a waterproofing layer
To contain seepage losses in existing above-ground tanks
As flexible forms where loss of material cannot be allowed.

Related Research Articles

A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed.

Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve civil engineering problems. This includes eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosynthetic clay liners, geofoam, geocells and geocomposites. The polymeric nature of the products makes them suitable for use in the ground where high levels of durability are required. They can also be used in exposed applications. Geosynthetics are available in a wide range of forms and materials. These products have a wide range of applications and are currently used in many civil, geotechnical, transportation, geoenvironmental, hydraulic, and private development applications including roads, airfields, railroads, embankments, retaining structures, reservoirs, canals, dams, erosion control, sediment control, landfill liners, landfill covers, mining, aquaculture and agriculture.

High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes and plastic lumber. HDPE is commonly recycled, and has the number "2" as its resin identification code.

Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or underwater to specified depths.

<span class="mw-page-title-main">Linear low-density polyethylene</span> Polymer

Linear low-density polyethylene (LLDPE) is a substantially linear polymer (polyethylene), with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. Linear low-density polyethylene differs structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching. The linearity of LLDPE results from the different manufacturing processes of LLDPE and LDPE. In general, LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and such higher alpha-olefins as butene, hexene, or octene. The copolymerization process produces an LLDPE polymer that has a narrower molecular weight distribution than conventional LDPE and in combination with the linear structure, significantly different rheological properties.

Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. Typically made from polypropylene or polyester, geotextile fabrics come in two basic forms: woven and nonwoven.

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

A pond liner is an impermeable geomembrane used for retention of liquids, including the lining of reservoirs, retention basins, hazardous and nonhazardous surface impoundments, garden ponds and artificial streams in parks and gardens.

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

Geocomposites are combinations of two or more geosynthetic materials for civil engineering applications that perform multiple geosynthetic functions. Such composite materials enhance technical properties of the soil or the geotechnical structure, while minimizing application costs.

<span class="mw-page-title-main">Geosynthetic clay liner</span> Low hydraulic conductivity geomembrane with bentonite encapsulated in a geotextile

Geosynthetic clay liners (GCLs) are factory manufactured hydraulic barriers consisting of a layer of bentonite or other very low-permeability material supported by geotextiles and/or geomembranes, mechanically held together by needling, stitching, or chemical adhesives. Due to environmental laws, any seepage from landfills must be collected and properly disposed of, otherwise contamination of the surrounding ground water could cause major environmental and/or ecological problems. The lower the hydraulic conductivity the more effective the GCL will be at retaining seepage inside of the landfill. Bentonite composed predominantly (>70%) of montmorillonite or other expansive clays, are preferred and most commonly used in GCLs. A general GCL construction would consist of two layers of geosynthetics stitched together enclosing a layer of natural or processed sodium bentonite. Typically, woven and/or non-woven textile geosynthetics are used, however polyethylene or geomembrane layers or geogrid geotextiles materials have also been incorporated into the design or in place of a textile layer to increase strength. GCLs are produced by several large companies in North America, Europe, and Asia. The United States Environmental Protection Agency currently regulates landfill construction and design in the US through several legislations.

A landfill liner, or composite liner, is intended to be a low permeable barrier, which is laid down under engineered landfill sites. Until it deteriorates, the liner retards migration of leachate, and its toxic constituents, into underlying aquifers or nearby rivers, causing potentially irreversible contamination of the local waterway and its sediments.

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

Cellular confinement systems (CCS)—also known as geocells—are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention. Typical cellular confinement systems are geosynthetics made with ultrasonically welded high-density polyethylene (HDPE) strips or novel polymeric alloy (NPA)—and expanded on-site to form a honeycomb-like structure—and filled with sand, soil, rock, gravel or concrete.

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.

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.

References

1 2 Koerner, R. M. (2012). Designing With Geosynthetics (6th ed.). Xlibris Publishing Co., 914 pgs.
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.