Coal Mining, Design and Methods of


The Pennsylvania State University University Park, Pennsylvania United States

usually described by the quantity of weight, ex­pressed in tons contained within a specified boundary in plan. Tonnage for a reserve can be quantified several ways that include raw in-place tons, raw recoverable tons, and salable tons.


1.1 Coal Geology

Coal seams originate and are formed by the consolidation of biota, minerals, and natural chemi­cals through geologic time. Compression, heat, sedi­mentation, erosion, and chemical energy are agents of the coal formation process.

Multiple coal seams can exist in a reserve, with each coal seam separated by sedimentary rock interburden. Coal, and the rock above and below the coal seam, is primarily layered sedimentary rock in origin, as opposed to igneous or metamorphic rock. The noncoal layers are usually sandstone, limestone, shale, siltstone, and mudstone. The layers can be very symmetric and consistent in thickness, or they can appear in the reserve in nonregular patterns such as sandstone channels, which can exist above the coal seam or replace the coal seam by scouring during geologic formation. Sandstone channels can also create vertical downward displacement of the coal seam by differential compaction. Chemical and heat processes during mineral formation can also produce small pockets of nonsedimentary rock within the coal seam and surrounding rock such as iron pyrite, mica, and other minerals. These miner­als, depending on their hardness, can interrupt the mining process as most coal mining methods are designed to extract soft mineral having uniaxial compressive strength less than 6000 psi to 8000 psi.

Coal Mining, Design and Methods of Coal Mining, Design and Methods of

The processes of the geologic environment in which the coal was formed determines the end characteristics of the coal seam, such as thickness, seam pitch, energy value (generally quantified as BTU per lb), nonvolatile content, moisture content, depth below the surface, structure (faults, folds, rock fractures), the presence of an igneous intrusives called dikes, and characteristics of the rock immedi­ately above and below the coal seam. All of these characteristics affect the mine design and methods. Layered coal seams and surrounding rock thickness range from less than 1 ft to over 150 ft. Figure 1 shows a typical cross section of coal seams inter­spersed in layers of sandstone and shale.

Updated: December 20, 2015 — 6:04 am