The coal mining industry segment produces coal, a fossil fuel that is used primarily for the generation of electrical power and in the production of steel. Like oil, coal is formed over millions of years from plant and animal matter, but unlike oil, coal is a solid and therefore miners must go to earth to retrieve it. However, many coal seams are located near the surface, which makes it easy to extract this resource.
Open pit coal mining typically uses the method known as open pit mining, which is often more profitable than underground mining and requires fewer workers to produce the same amount of coal. In open pit mining, workers use massive earth-moving equipment, such as electric shovels or skid lines, to remove the layers of soil and rock that cover the coal seam.
Once the coal is exposed, it is broken up using explosives, and then smaller shovels lift it off the ground and load it onto trucks. Federal, state and local laws require mining companies to restore mined land after open pit mining is complete; as a result, the overburden and topsoil are stored after removal so that they can be replaced and the native vegetation replanted.
Underground mining is used when the coal deposit is far below the earth’s surface. When developing an underground mine, miners must first dig tunnels deep into the ground near where the coal is located. Depending on where the coal seam is in relation to the surface, the tunnels can be vertical, horizontal, or sloped. The entrances are built so that the miners can get themselves and their equipment to the ore and remove it, while allowing fresh air to enter the mine.
Once dug to the proper depth, the tunnels of a mine are interconnected with a network of corridors that go in many directions. Using the room and pillar method, miners remove sections of the coal as they work in the coal seam from the tunnel entrance to the edge of the mine property, leaving columns of coal in place to help hold the roof together. with long steel bolts. This process is then reversed and the rest of the ore is mined, while the miners work their way back.
In the case of longwall coal mining, self-advancing roof supports, made of hydraulic jacks and metal plates, cover the area being mined. As the coal is removed, the entire apparatus moves forward, allowing the roof in the mined area to collapse as the miners return towards the tunnel entrance. Underground mining does not require as extensive a reclamation process as open pit mining; however, mine operators and environmental engineers must ensure that groundwater remains uncontaminated and that abandoned mines do not collapse.