Geomembranes are impermeable membranes used in conjunction with rocks or earth to block fluid migration in man-made structures. In most cases, they are made of synthetic polymers. Unlike other methods of controlling fluid movement, such as using clay, asphalt, or sand stabilized with cement, these membranes have almost no permeability if there are no holes in the material. Due to their flexibility, they can accommodate ground settling and shifting. Geomembranes may also be called synthetic liners, polymeric membranes, or flexible membrane liners.
Geomembranes are most often made of polyvinyl chloride (PVC), medium-density polyethylenes, chlorosulfonated polyethylene, or a similar kind of material. Due to their ability to block fluids, they can help to prevent the dispersal of contaminants, and may be used with soil liners or geotextiles to create a composite lining system that provides added security. Geotextile fabrics, made from polyester or polypropylene, are used with soil to provide filtration, reinforcement, or drainage in many civil engineering applications such as embankments, canals, and railroads.
Landfills are lined with geomembranes to keep leachate from polluting the nearby environment.
These membranes are mainly used as liners in landfills to help prevent chemicals or other dangerous leachate from polluting the surrounding area. When a landfill reaches its maximum capacity, a geomembrane final cover is often placed over it to prevent the escape of gases and the intrusion of rain. These membranes have many other applications, however, and are useful wherever liquid movement needs to be controlled or prevented. They may be used for something as simple as building a decorative pond, or as potentially hazardous as containing a spill from a chemical storage tank. They may be used in mining to help contain chemical solutions or to reduce the loss of metals that are leached out of ore.
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Tunnels may require the use of geomembranes to prevent unwanted leakage and to direct drainage.
When preparing an area for geomembrane installation, the soil must be freed of all sharp objects such as sticks that could puncture the lining; if necessary, geotextiles can be placed below to reduce the risk of tears. Panels of geomembrane lining are usually bonded at adjacent seams, using extrusion welding, hot-wedge seaming, or hot-air welding. Generally, hot-air welding is used as a temporary measure to immobilize the lining before an extrusion weld is applied. Seams are subsequently tested to ensure that there are no leaks and that they are properly joined.
Geomembranes are used by many companies and contractors in an effort to minimize the effect of human development activities on the environment. Thus, although geomembrane liners used in many applications, they are especially important for waste containment. They are manufactured from highly durable materials, often with an expected lifetime of hundreds of years. They must be resistant to chemicals and to wear, so that the passage of time and corrosion do not affect the integrity of the lining and the environment is protected.