Coal mining [1] is the removal of coal from the ground. The mining method employed to extract the coal depends on the following criteria: a. seam thickness [2], b. the overburden thickness, c. the ease of removal of the overburden, d. the ease with which a shaft [3] can be sunk to reach the coal seam, e. the amount of coal extracted relative to the amount that cannot be removed, and f. the market demand for the coal.

The two types of mining methods are surface mining [4] and underground mining [5]. In surface mining, the layers of rock or soil overlying a coal seam are first removed after which the coal is extracted from the exposed seam. In underground mining, a shaft is dug to reach the coal seam. Currently, underground mining accounts for approximately 60 percent of the world recovery of coal.

5-1 Surface Mining

Surface mining is used to reach coal reserves that are too shallow to be reached by other mining methods. Types of surface mining include open-pit mining [6], drift mining [7], slope mining [8], contour mining [9], and auger mining [10].

A. Open-pit Mining

In open-pit mining, or strip mining, earth-moving equipment is used to remove the rocky overburden and then huge mechanical shovels [11] scoop [12] coal up from the underlying deposit. The modern coal industry has developed some of the largest industrial equipment ever made, including shovels capable of holding 290 metric tons of coal.

To reach the coal, bulldozers [13] clear the vegetation and soil. Depending on the hardness and depth of the exposed sedimentary rocks, these rocky layers may be shattered with explosives. To do this, workers drill blast holes [14] into the overlying sedimentary rock, fill these holes with explosives [15], and then blast the overburden to fracture the rock. Once the broken rock is removed, coal is shoveled from the underlying deposit into giant earth-moving trucks [16] for transport [17].

B. Drift Mining

Drift mining is used when a horizontal seam [18] of coal emerges at the surface on the side of a hill or mountain, and the opening [19] into the mine can be made directly into the coal seam. This type of mining is generally the easiest and most economical type because excavation through rock is not necessary. If coal is available in this manner, it is likely to be mined.

C. Slope Mining

Slope mining occurs when an inclined opening is used to tap the coal seam (or seams). A slope mine may follow the coal seam if the seam is inclined and exposed to the surface, or the slope may be driven through rock strata overlying the coal to reach a seam. Coal transportation from a slope mine can be accomplished by conveyor [20] or by track haulage [21] (using a trolley locomotive [22] if the grade is not severe) or by pulling mine cars [23] up the slope using an electric hoist [24] and steel rope [25] if the grade is steep. The most common practice is to use a belt conveyor.

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