A geomembrane is 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.
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.
Geomembranes dominate the sales of geosynthetic products, at 1.8 billion USD per year worldwide, which is 35% of the market. The US market is currently divided between HDPE, LLDPE, fPP, PVC, CSPE-R, EPDM-R and others (such as EIA-R), and can be summarized as follows: (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%). Perhaps the greatest increases will be seen in the containment of coal ash and heap leach mining for precious metal capture.
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.
The main physical properties of geomembranes in the as-manufactured state are:
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.
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.
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:
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.
Geomembranes have been used in the following environmental, geotechnical, hydraulic, transportation, and private development applications:
Canal lining is the process of reducing seepage loss of irrigation water by adding an impermeable layer to the edges of the trench. Seepage can result in losses of 30 to 50 percent of irrigation water from canals, so adding lining can make irrigation systems more efficient. Canal linings are also used to prevent weed growth, which can spread throughout an irrigation system and reduce water flow. Lining a canal can also prevent waterlogging around low-lying areas of the canal.By making a canal less permeable, the water velocity increases resulting in a greater overall discharge. Increased velocity also reduces the amount of evaporation and silting that occurs, making the canal more efficient. The oldest known paved canal was discovered in 1995 near the pyramids of Giza, and is estimated to be around 4,500 years old.Electrical liner integrity survey
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.Fabricated geomembranes
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.
Fabricated geomembranes are geomembranes that are flexible enough to be seamed or welded into large panels in a factory, folded, transported to the project site, unfolded without creasing or damage, and field seamed and tested as necessary. These geomembranes are relatively thin (usually less than 45 mils, [1.1 mm] thick), flexible, and can be reinforced with fabrics. Fabricated geomembranes can be accordion folded or rolled up to facilitate deployment and reduce double folds as shown in photographs.Factory fabrication reduces field seaming by 70 to 90% depending on the geometry of the installation and weight of the geomembrane material used, which reduces field testing and patching, installation time, and overall cost. The panel size is limited only by the allowable shipping weight, which depends on the mode of transportation. The reduction of installation time and testing is particularly important in harsh environments which can extend the “field installation season”. Fabricated panels can be large enough to create “drop-in” liners that do not require any field seaming, testing, or patching which speeds installation and improves quality. Fabricated geomembranes also allow a more modular construction approach which results in less resources having to be committed to one location for an extended period, e.g., personnel and deployment, welding, and testing equipment. Modular construction also adds more predictability to project scheduling by reducing weather, transportation, site access, testing and data interpretation, and labor issues.Final cover
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.A final cover system can include a top soil layer composed of nutrient rich soil, a protective layer to reduce the effects of freeze/thaw, a drainage layer which moves storm water, a barrier layer, and a grading layer.Geocomposite
The basic philosophy behind geocomposite materials is to combine the best features of different materials in such a way that specific applications are addressed in the optimal manner and at minimum cost. Thus, the benefit/cost ratio is maximized. Such geocomposites will generally be geosynthetic materials, but not always. In some cases it may be more advantageous to use a nonsynthetic material with a geosynthetic one for optimum performance and/or least cost. As seen in the following, the number of possibilities is huge — the only limits being one's ingenuity and imagination.
There are five basic functions that can be provided: separation, reinforcement, filtration, drainage, and containment.Geosynthetic clay liner
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.Geosynthetics
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.Geotextile
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 three basic forms: woven (resembling mail bag sacking), needle punched (resembling felt), or heat bonded (resembling ironed felt).
Geotextile composites have been introduced and products such as geogrids and meshes have been developed. Geotextiles are able to withstand many things, are durable, and are able to soften a fall if someone falls down. Overall, these materials are referred to as geosynthetics and each configuration—geonets, geosynthetic clay liners, geogrids, geotextile tubes, and others—can yield benefits in geotechnical and environmental engineering design.Gravel
Gravel is a loose aggregation of rock fragments. Gravel is classified by particle size range and includes size classes from granule- to boulder-sized fragments. In the Udden-Wentworth scale gravel is categorized into granular gravel (2 to 4 mm or 0.079 to 0.157 in) and pebble gravel (4 to 64 mm or 0.2 to 2.5 in). ISO 14688 grades gravels as fine, medium, and coarse with ranges 2 mm to 6.3 mm to 20 mm to 63 mm. One cubic metre of gravel typically weighs about 1,800 kg (or a cubic yard weighs about 3,000 pounds).
Gravel is an important commercial product, with a number of applications. Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or asphalt; Russia alone has over 400,000 km (250,000 mi) of gravel roads. Both sand and small gravel are also important for the manufacture of concrete.Hickory Ridge Landfill
The Hickory Ridge Landfill is a municipal solid waste landfill located in Conley, Georgia, United States and privately owned by Republic Services. The site was opened in 1993 and closed in 2006; it contains nearly 9,000,000 cubic yards of waste.
The Hickory Ridge Landfill was capped in October 2011 with a dual-purpose landfill closure system referred to as an Exposed Geomembrane Solar Cover (EGSC). Developed by Carlisle Energy Services, the closure system provides renewable electricity via (photovoltaic) solar panels,
The project is the second installation of an EGSC and is the world's largest installed system of its kind. At the time of commissioning it was the largest solar photovoltaic system in the state of Georgia. It also represents a $5,000,000 investment by Republic Services supported by a $2,000,000 grant from the Georgia Environmental Finance Authority (GEFA).High-density polyethylene
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.
In 2007, the global HDPE market reached a volume of more than 30 million tons.Jean-Pierre Giroud
Jean-Pierre Giroud (born 1938) is a French geotechnical engineer and a pioneer of geosynthetics.
Giroud has developed a number of detailed design methods used in geosynthetics engineering with more than 47 years of experience. Some of the design methods are liner leakage evaluation, drainage systems, leachate collection and leakage detection layers, liner system stability, reinforcement of liners and soil layers overlying voids, geomembrane stress and strain analysis, evaluation of geomembrane properties, connections between geomembranes and rigid structures, geomembrane uplift by wind and so on.Jibiya Dam
The Jibiya Dam is in Jibiya local government area of Katsina State in the north of Nigeria. It is an earth-fill structure with a geomembrane liner, with a height of 23.5 m and a total length of 3,660 m, and has a capacity of 142 million m3.
The dam was designed in 1987 and completed in 1989, and was built to support irrigation and water supply.
The landscape at the dam site is sub-desertic except in the rainy season.
The Gada river flows for only about four months each year, with a catchment area at Jibiya of over 400 km2.
Due to the loose sandy nature of the surface soil, a flexible impervious liner was used that could adapt to settling or deformation of the embankment.An assessment of the dam in 2004 rated its condition "good" but noted that no instrument readings had been made since 1994 due to lack of training of the operators.
As of 2007, the dam was not being used for irrigation due to lack of fuel to run the pumps.
The Gada River flows from Nigeria into Niger and then back into Nigeria. In the past, it was dry for eight months of the year. There is now a regulated flow throughout the year, which has improved the water supply in Niger.Landfill liner
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 spoliation of the local water.
Modern landfills generally require a layer of compacted clay with a minimum required thickness and a maximum allowable hydraulic conductivity, overlaid by a high-density polyethylene geomembrane.
The United States Environmental Protection Agency has stated that the barriers "will ultimately fail," while the site remains a threat for "thousands of years," suggesting that modern landfill designs delay but do not prevent ground and surface water pollution.Chipped or waste tires are used to support and insulate the liner.Pond liner
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.Salt Springs Reservoir
Salt Springs Reservoir is a reservoir in the eastern portions of Amador County and Calaveras County of California in the Sierra Nevada about 30 miles (48 km) east-northeast of Jackson. The reservoir is in the Eldorado National Forest at an elevation of 3,900 feet (1,200 m).
The 141,900 acre foot (175,000,000 m3) reservoir is formed by Salt Springs Dam on the North Fork of the Mokelumne River. The concrete-faced rock-fill dam is 332 feet (101 m) tall and was completed in 1931. It is owned by Pacific Gas and Electric and its sole purpose is hydroelectricity production, though limited recreation is available. A short pipeline from the reservoir conveys water to the 44 MW Salt Springs Powerhouse. Some of the water is returned to the river downstream, but much of it flows into the Tiger Creek Conduit, a concrete flume that moves water downstream for use in other powerhouses in PG&E's Mokelumne River Project (FERC Project 137).
The dam has a history of settlement problems caused by poor consolidation of the rocks during construction. The concrete face has been cracked many times by the movement, causing leaks. The surface of the dam consists of cracks, craters and shotcrete overlays. It was decided to use a flexible geomembrane to cover the portions of the dam with the greatest leakage. The installation of the membrane was completed in 2005.
The dam is being examined as the lower pool in a 380-1,140 MW pumped-storage project with the Bear River Dam as the upper pool.Seathwaite Tarn
Seathwaite Tarn is a reservoir in the Furness Fells within the English Lake District. It is located to the south of Grey Friar and to the west of Brim Fell (on the ridge between The Old Man of Coniston and Swirl How) and north east of the village of Seathwaite on the east of the Duddon Valley.
In order to create a source of drinking water the existing tarn was considerably enlarged with a dam in 1904. During the dam construction some of the navvies rioted damaging buildings in the village, several rioters were shot, one dying the next day.
The dam is almost 400 yards (366 m) long and is concrete cored with slate buttresses, the resulting depth of the tarn being around 80 feet (24 m). Water is not abstracted directly from the tarn, but flows some distance downriver to an off-take weir.
On the slopes of Brim Fell, above the head of the reservoir, are the remains of Seathwaite Tarn Mine. This was worked for copper in the mid 19th century, and also appears as a location in the novel The Plague Dogs by Richard Adams. Rocks in the area were the first confirmed occurrence of wittichenite in the British Isles.Bronze Age ring cairns were found close to Seathwaite Tarn in 2003, these were excavated in 2003 and 2007.Seathwaite Tarn has suffered from acidification. An experiment in 1992–1993 to reduce the acidification by using a phosphorus-based fertiliser increased the pH from 5.1 to 5.6 and changed the levels of the different species of the rotifer assemblage significantly.Silt
Silt is granular material of a size between sand and clay, whose mineral origin is quartz and feldspar. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water (also known as a suspended load) and soil in a body of water such as a river. It may also exist as soil deposited at the bottom of a water body, like mudflows from landslides. Silt has a moderate specific area with a typically non-sticky, plastic feel. Silt usually has a floury feel when dry, and a slippery feel when wet. Silt can be visually observed with a hand lens, exhibiting a sparkly appearance. It also can be felt by the tongue as granular when placed on the front teeth (even when mixed with clay particles).Trench
A trench is a type of excavation or depression in the ground that is generally deeper than it is wide (as opposed to a wider gully, or ditch), and narrow compared with its length (as opposed to a simple hole).In geology, trenches are created as a result of erosion by rivers or by geological movement of tectonic plates. In the civil engineering field, trenches are often created to install underground infrastructure or utilities (such as gas mains, water mains or telephone lines), or later to access these installations. Trenches have also often been dug for military defensive purposes. In archaeology, the "trench method" is used for searching and excavating ancient ruins or to dig into strata of sedimented material.