Geomembranes are thin plastic sheets that are essentially impervious and are used to prevent leakage from liquid or solid-storage facilities. [1] 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 [2] 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. [3]
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. [3] 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.
Fabricated geomembranes can be used for a variety of applications including in alphabetical order: aquaculture, baffle curtains, canals, decorative ponds, deicing fluid ponds, drill pad liners for oil and gas development, exposed or floating covers, fertilizer containment, golf course ponds, hydrocarbon containment, landfill liners and covers, mine tailings ponds and heap leach pads, reservoirs, sewage lagoons, tank liners, and wastewater ponds. [3]
Flexible geomembranes are fabricated into panels the size of which is controlled by the allowable shipping and handling weight. It is common to ship panels that weigh 1,816 kg (4,000 Ibs.) but panels as heavy as 4,086 kg (9,000 Ibs.) have been shipped.
After moving the panel to the proper deployment location as indicated on the Panel Layout Diagram for the project, the panel is unfolded or unrolled from the shipping pallet. The pallet is usually on a front-end loader or forklift which moves backwards to facilitate unfolding or unrolling of the panel. Pulling the geomembrane panel off the pallet or the roll by a chain is not recommended because it may damage the geomembrane. Deployment personnel are then positioned approximately 4.6 m (15 ft) apart along the edges of the panel to unfold and move the panel into the proper location. If the edge to be gripped is to be subsequently welded or bonded, the panel edge is folded back about 0.6 to 1.0 m (2.0 to 3.3 ft), creating a fold. The fold is gripped using the 0.3 m long by 10 mm (1-foot long by 2 inch) diameter smooth wooden dowel or a smooth grade stake rather than the edge itself. This is to avoid stretching the panel edge where it is to be bonded to another panel. As the panel is pulled out, it is necessary to maintain air under the geomembrane to reduce friction with the ground surface. This can be accomplished by holding the panel edge and advancing at a rate fast enough to create air under the geomembrane as it is unfolded. Another method is to “fan” air under the geomembrane by raising and lowering the edge of the panel to create a wave-like action across the liner as it is being spread. After the panel is set in the exact position, it is welded or bonded to adjacent panels.
Electric resistance welding (ERW) is a welding process where metal parts in contact are permanently joined by heating them with an electric current, melting the metal at the joint. Electric resistance welding is widely used, for example, in manufacture of steel pipe and in assembly of bodies for automobiles. The electric current can be supplied to electrodes that also apply clamping pressure, or may be induced by an external magnetic field. The electric resistance welding process can be further classified by the geometry of the weld and the method of applying pressure to the joint: spot welding, seam welding, flash welding, projection welding, for example. Some factors influencing heat or welding temperatures are the proportions of the workpieces, the metal coating or the lack of coating, the electrode materials, electrode geometry, electrode pressing force, electric current and length of welding time. Small pools of molten metal are formed at the point of most electrical resistance as an electric current is passed through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are limited to relatively thin materials.
A flat roof is a roof which is almost level in contrast to the many types of sloped roofs. The slope of a roof is properly known as its pitch and flat roofs have up to approximately 10°. Flat roofs are an ancient form mostly used in arid climates and allow the roof space to be used as a living space or a living roof. Flat roofs, or "low-slope" roofs, are also commonly found on commercial buildings throughout the world. The U.S.-based National Roofing Contractors Association defines a low-slope roof as having a slope of 3 in 12 (1:4) or less.
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.
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.
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.
Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.
A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid 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.
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.
Pallet rack is a material handling storage aid system designed to store materials on pallets. Although there are many varieties of pallet racking, all types allow for the storage of palletized materials in horizontal rows with multiple levels. Forklift trucks are usually required to place the loaded pallets onto the racks for storage. Since the Second World War, pallet racks have become a ubiquitous element of most modern warehouses, manufacturing facilities, retail centers, and other storage and distribution facilities. All types of pallet racking increase storage density of the stored goods. Costs associated with the racking increases with increasing storage density.
A fabric structure is a structure made of fabric, with or without a structural frame made from the weaving of the fabric itself. The technology provides end users a variety of aesthetic free-form building designs. Custom-made structures are engineered and fabricated to meet worldwide structural, flame retardant, weather-resistant, and natural force requirements. Fabric structures are considered a sub-category of tensile structure.
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).
Copper has earned a respected place in the related fields of architecture, building construction, and interior design. From cathedrals to castles and from homes to offices, copper is used for a variety of architectural elements, including roofs, flashings, gutters, downspouts, domes, spires, vaults, wall cladding, and building expansion joints.
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.