How is shallow coal removed

Slope mines usually begin in a valley bottom, and a tunnel slopes down to the coal to be mined. Shaft mines are the deepest mines; a vertical shaft with an elevator is made from the surface down to the coal. In western Kentucky, one shaft mine reaches 1, feet below the surface.

In room and pillar mining, the most common type of underground coal mining, coal seams are mined by a continuous miner that cuts a network of "rooms" into the seam.

As the rooms are cut, the continuous miner simultaneously loads the coal onto a shuttle or ram car, from which it will eventually be placed on a conveyor belt that will move it to the surface. Each room alternates with a pillar of greater width than the excavated room for support. Using this mining method normally results in a reduction in recovery of as much as 60 percent, because of coal being left in the ground as pillars. As mining continues, roof bolts are placed in the ceiling to prevent ceiling collapse.

Under special circumstances, pillars may sometimes be removed or pulled toward the end of mining in a process called retreat mining. Removing support during retreat mining can lead to roof falls, so the pillars are removed in the opposite direction from which the mine advanced: hence the term retreat mining.

Longwall mining is another type of underground mining. Mechanized shearers are used to cut and remove the coal at the face of the mine. After the coal is removed, it drops onto a chain conveyor, which moves it to a second conveyor that will ultimately take the coal to the surface. Temporary hydraulic-powered roof supports hold up the roof as the extraction process proceeds. This method of mining has proven to be more efficient than room and pillar mining, with a recovery rate of nearly 75 percent, but the equipment is more expensive than conventional room and pillar equipment, and cannot be used in all geologic circumstances.

In longwall mining, only the main tunnels are bolted. Most of the longwall panel is allowed to collapse behind the shields which hold the roof as coal is excavated.

Surface-mining methods include area, contour, mountaintop removal, and auger. Area mines are surface mines that remove shallow coal over a broad area of fairly flat land. Huge dragline shovels remove rocks overlying the coal called overburden. After the coal has been removed, the rock is placed back into the pit.

Contour mines recover coal in steep, hilly, or mountainous terrain. A wedge of overburden is removed along the coal outcrop on the side of a hill, forming a bench at the level of the coal. After the coal is removed, the overburden is placed back on the bench to return the hill to its natural slope. Mountaintop- removal mines are special area mines used where several thick coal seams occur near the top of a mountain.

Large quantities of overburden are removed from the top of the mountain , and this material is used to fill in valleys next to the mine.

Augur mines are operated on surface-mine benches before they are covered up ; the coal in the side of the hill that can't be reached by contour mining is drilled or augured out. Drift, contour, mountaintop- removal, and augur mining are more common in the Eastern Kentucky Coal Field, and area, slope, and shaft mining are more common in the Western Kentucky Coal Field.

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Free statement of participation on completion of these courses. Create your free OpenLearn profile. Course content Course content. Energy resources: Coal Start this free course now. Free course Energy resources: Coal. Question 5 Figure 13 shows a cross-section through coal-bearing rocks. Answer The coal seam covers 76 mm 2 squares, whereas the overburden covers 21 cm 2 squares, i.

Figure 13 A cross-section through coal bearing rocks. For use with Question 5. Note that areas on this cross-section are proportional to volumes of rock. The lines showing the mine limit are at angles where bare rock surfaces are stable, so that the mine walls do not collapse during operations. Figure 14 Three-dimensional computer model showing two stages in the development of a surface mine. The pink area shows the projected development of the coalface through time.

Previous 2. Next 2. These include strip mining, open-pit mining, mountaintop removal, dredging and highwall mining. Surface mining is often the preference for mining companies. This is because removing the terrain surface, or overburden, to access the mineral beneath is often more cost-effective than gouging tunnels and subterranean shafts to access minerals underground. Soil, rock, and vegetation over the mineral seam is removed with huge machines, including bucket-wheel excavators.

This type of mining makes sense when the mineral is near the surface. If the ore is too far under the surface, the process of strip mining becomes impractical and needlessly damaging to the terrain. Two types of strip mining exist, depending on the amount of ore under the surface, and the surrounding terrain.

They are:. Open-pit mining is similar to strip mining, except the ore is removed from an open pit which is not then filled in. Open-pit mining has been around for centuries, with ancient cultures like the Greeks, Romans, and Persians mining for granite, marble and even salt. Open-pit mines are commonly called quarries when they produce materials used in building: limestone, granite, and marble, for example. These pit mines continue to be enlarged until there is no more ore to mine or the overburden becomes too heavy.