Next, the operator backfills the pit with previously extracted overburden and grades it. The operator then extracts the coal and transports it to a power plant or to a rail line for shipment to a power plant.

Large machines remove the overburden in successive layers until the coal seam is reached.

Typical open pit mining method with thick coal seam. Typically, several different pits, at various stages of development or reclamation, are being worked at any given time on a single site. The overburden may be placed on adjacent, undisturbed land, or it may be transported by belt or rail to the other end of the same mine or to an exhausted mine that needs to be backfilled. In open pit mining, the operator first removes the overburden to uncover the coal seam. Nonetheless, the sheer size and capacity of these mines necessitates substantial surface disturbance. The thick coal seams found at these large mines ensure that the amount of land disturbed for each ton of coal produced is much smaller than for most Eastern and Midwestern mines. Production levels may exceed 10 million tons of coal per year. Open pit mines are usually large operations. The technique is common in the western United States (and other parts of the world) where very thick - 50 to 100 foot - coal seams exist. Open pit mining is similar to area mining. Mining may cease in a particular area, for example, where the coal seam becomes thinner or where the seam dips further below the surface. This process continues along parallel strips of land so long as the ratio between the overburden and the coal seam, called the stripping ratio, makes it economically feasible to recover coal. The backfilled pit is then covered with topsoil and seeded. The operator places the overburden from the second cut into the trench created by the first cut and grades and compacts the spoil. After extracting the coal from the first cut, the operator makes a second, parallel cut. In large mines, huge stripping shovels or draglines remove the overburden.

The operator places spoil from the box cut on the side away from the direction in which mining will progress. Following scalping of the vegetation and topsoil removal, area mining begins with an initial rectangular cut (called the box cut ).Īrea strip mining with concurrent reclamation. Area mines excavate large rectangular pits, developed in a series of parallel strips or cuts which may extend several hundred yards in width and more than a mile in length. Area mining is the technique most often employed in the flat or gently rolling countryside of the Midwest and western United States.

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