Читать книгу Coal-Fired Power Generation Handbook - James Speight G., James G. Speight - Страница 52

The characteristic that distinguishes this type of mine is essentially the thickness of the coal seam insofar as it is virtually impossible to backfill the immediate mined out area with the original overburden when extremely thick seams of coal are involved. Thus, the coal is removed either by taking the entire seam down to the seam basement (i.e., floor of the mine) or by benching. This latter technique involves the staged mining of the coal seam and has been employed with considerable success not only in many coal mines but also for the mining of the Athabasca oil sand deposits in northern Alberta (Canada), where the tar sand pay zone (ore body) may be some 200 feet (60 m) deep (Speight, 1990, 2013, 2020). If, however, significant parting exists on the floor of the mine from where the coal has recently been removed, this immediate worked out section will not be available for receipt of the overburden and in such a case the overburden may have to be transported from the area.

Frequent use is made of a drift mine in which a horizontal seam of coal outcrops to the surface in the side of a hill or mountain, and the opening into the mine can be made directly into the coal seam. This type of mine is generally the easiest and most economical to open because excavation through rock is not necessary.