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Mine Types and Mining Methods

The mine type is indicated on the map by color: green represents surface mines; orange and yellow represent underground mines. The orange shade is used for areas of underground mining that are documented by a primary or secondary source map. A yellow shade is used for cases where no map of the mine workings is available, but a general area of mining can be inferred from property maps or production figures. Shade patterns are used to distinguish the two primary methods used in underground mines: room-and-pillar and high-extraction.

The method used gives some indication of the amount and pattern of coal extraction within each mined area, and has some influence on the timing and type of subsidence that can occur over a mine. The following discussion and illustrations of mining methods are based on Guither et al. (1984):

In room-and-pillar mines, coal is removed from selected areas called rooms. Pillars of unmined coal are left between the rooms to support the roof. Depending on the size of rooms and pillars, the amount of coal removed from the production areas will range from 40% to 70%.

Room-and-pillar mining is divided into the following six categories, which correspond to the first six symbols shown on the mining-method key:

  1. RP: Room and Pillar general: a classification used when the specific type of room-and-pillar mining is unknown
  2. RPB: Room-and-pillar Basic
  3. MRP: Modified Room and Pillar
  4. RPP: Room-and-Pillar Panel
  5. BRP: Blind Room and Pillar
  6. CRP: Checkerboard Room and Pillar
Blind and checkerboard are the most common types of room-and-pillar mining used in Illinois today. The knowledge of room-and-pillar mining methods gives a trained engineer information on the nature of subsidence that may occur. A more extensive discussion of subsidence can be found in DuMontelle et al. (1981).

High-extraction mining methods are subdivided into high-extraction retreat (HER) and longwall (LW). In these methods, much of the coal is removed within well defined areas of the mine. Subsidence of the surface above these areas is low; however, subsidence may continue for several years after mining.

Although longwall mines are undifferentiated on the symbol key, a significant change in mining technique about 1960 allows existing longwall mines to be categorized by date into 2 groups: those before and those after 1960.

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