Underground mining or deep mining is the method used in most Illinois coal production.

Traditionally speaking, this is the process most individuals associate with coal mining. However, many people are not aware of the significant advancements in recent years, such as widespread mechanization and computerization of operations, which have made deep mining considerably more efficient than in the past.

Deep mining is required when coal seams (beds of coal) lie deeper than 200 feet beneath the surface of the earth. The depth of most underground mines in the country is less than 1,000 feet, but a few are 1,500 to 2,000 feet deep. To reach the coal in these operations, miners are transported from the surface down into the mines either by elevators or by cars traveling on railroad tracks down a sloped entrance into the earth.

A deep mine must be kept highly ventilated and well drained. Underground mining using the room and pillar method normally recovers about 50 percent of the coal. With a longwall mining system, recovery of coal can be 80 to 90 percent.

Much of the coal mined in deep facilities in the United States still is produced by continuous mining machines, some of which can cut coal from the face of a coal seam at a rate of four to 15 tons per minute. Continuous mining is a method of underground mining using a machine that does the entire coal extracting job, eliminating the traditional four-step cycle of cutting, drilling, blasting and loading. The continuous mining machine moves up to the seam, cuts coal from it and simultaneously conveys the coal to a shuttle car or conveyor belt for removal from the mine.

Another advanced mining technique used in Illinois, and elsewhere, is the longwall method. In longwall mining, the coal is mined by a rotating cutting drum that moves back and forth along a lengthy coal face called a longwall. The severed coal spills into a conveyor system for movement out of the mine.

During the mining, a series of steel shields or props, like giant piano keys, support the mine roof and protect the operator. As the cutting machine progresses through the coal, the shields and the rest of the system advance, allowing collapse of the roof in the mined out areas behind them.

Safety of miners is enhanced greatly with longwall mining because they are always protected by the steel canopies of the shield supports.

Concern over health and safety in underground mining has been the primary factor behind many of the operating improvements.