What is Longwall Mining?
Longwall mining is a deep mining technique capable of fully extracting huge panels of coal, frequently up to 1,500 feet wide and two miles long. When this coal (often 400-800 feet below the earth’s surface) is extracted, it leaves no support behind and almost always causes subsidence to both the natural and man-made structures. Coal companies that practice longwall mining are allowed, by law, to cause damage to structures, including homes. They are also allowed to disrupt water supplies. Coal companies are required to fund repairs to homes and to replace water supplies, but frequently residents find themselves embroiled in lengthy battles with these companies to have their living conditions restored. Some Effects of Longwall Mining: • PONDING: as a result of subsidence, wetlands are frequently created in areas that were previously dry. • The release of METHANE gas into the atmosphere, water and homes. At least one home explosion has been documented as a result. • Subsidence of RAILROAD
Longwall mining is a highly productive underground coal mining technique. Longwall mining machines consist of multiple coal shearers mounted on a series of self-advancing hydraulic ceiling supports. The entire process is mechanized. Longwall mining machines are about 800 feet (240 meters) in width and 5 to 10 feet (1.5 to 3 meters) tall. Longwall miners extract “panels” – rectangular blocks of coal as wide as the mining machinery and as long as 12,000 feet (3,650 meters). Massive shearers cut coal from a wall face, which falls onto a conveyor belt for removal. As a longwall miner advances along a panel, the roof behind the miner’s path is allowed to collapse. Longwall mining was first introduced in the 1950s and 1960s. Today it accounts for more than half of all coal production in the United States. On any given day, a typical longwall mining system is capable of extracting between 10,000 and 30,000 tons (9 to 27 million kilograms) of coal from a panel. The primary downside to this ver
One reason longwall mining succeeds in being the scourge of southwestern Pennsylvania is that the general public doesn’t have a clear notion of what longwall mining is. If you visualize a long wall, you probably have the wrong idea. Longwall is a form of underground mining that differs from traditional “room and pillar” mining in that no pillars or posts are left behind after the coal has been extracted. A longwall mining machine cuts along a 1000 foot-long coal face, going back and forth along the face, taking out all the coal. The machine has a protective shield that keeps the roof from falling on it. But as the machine advances, the roof – a layer of rock, frequently slate, sometimes sandstone or limestone – subsides more or less instantly. The machine will cut a swath 1000 feet wide and a mile or more long. As the rock immediately above the coal seam subsides, so do successive layers above that layer, until soon the subsidence reaches the surface, and the surface and contents subsi
A high-extraction mining method, longwall mining is a process of cutting between large panels of coal, isolating them from each other. A longwall mining machine, called a shearer, is set up alongside the panel and continuously shaves coal off the panel face, which can be anywhere from 800 to 1,500 feet wide. As the shearer advances, the mined coal is removed by conveyer belt also along the panel face and carried out of the mine. The roof is protected by hydraulic supports and steel shields on the shearer, and as the machine advances through the panel, the roof falls behind it, frequently causing subsidence damage on the earth’s surface.
