Coal mining voids

Figure 3 summarizes the principal environmental compartments that can in theory be affected by coal mining, as well as the principal potential environmental stresses that can arise from active and abandoned mine voids on the one hand, and from mine waste management facilities (i.e., spoil heaps and washery finings ponds) on the other. Further details on the mechanisms and impacts of these environmental stresses are given in Table 4 (for coal mine voids) and Table 5 (for coal mine wastes). 

Fig. 3. Flow diagram illustrating the principal environmental compartments affected by, and the principal environmental stresses that can arise from, active and abandoned coal mine voids and coal mine waste deposits.

Proffer a typology of the environmental impacts attributable to coal mining, distinguishing between those arising from bodies of mine waste and those arising from the mined voids themselves ... 

Monosized pieces in bulk, on the other hand, particularly if they are not spherical, do not reach high density or mass. For example, run-of-mine, coarsely crushed coal that is loaded into trucks, railroad cars, or ship holds results in relatively high bulk mass, as smaller particles fill the voids between larger ones. If that same coal is briquetted, the identical transport device holds much less and, therefore, in comparison, renders shipping less economical. Crushing briquettes and sizing the broken pieces to be within the same limits as run-of-mine coal results in identical bulk mass and meets standard loading requirements. 

Waste material from deep mines derives from the sinking of shafts, roadways, and ventilation tunnels, and extraction of the coal seam. This is then hauled to the surface and dumped locally. Previously, when coal was dug by hand, much of the waste was stored underground in voids. However, the implementation of modern mechanical techniques, particularly with the introduction of coal cutting machines on the coal faces, has dramatically increased the proportion of waste material. 

An example of void migration above a coal seam in an opencast mine, County Durham. England. 

The void fraction is, of course, extremely dependent on the particle size distribution and the capability of small particles to fill the void between larger ones. Hence, the lowest void fractions are reported from mine-run coal with broad particle size distributions aroimd 0.37. In usual particles sizes between 0.1 and 50 mm, the void fraction ranges between 0.38 and 0.60 strongly depending of the individual coal properties [10]. 

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