Geologic Factors Affecting Coal Mine Roof Stability in the Eastern United States

Abstract

Roof falls in underground coal mines are a continuing source of trouble for mine operators. Fatalities and injuries are a prominent concern, but lost time due to cleanup and disruption of mining operations presents an economic problem as well. Many geologic and geomechanical factors contribute to mine roof instability. These may be seen in rock core during exploration, or in the roof as mining progresses. Once these features are recognized, remedial action can then be taken. Geologic parameters attributed to roof falls in underground coal mines include both lithologic and structural discontinuities. The roof may be weakened where different lithologic materials are in contact with one another, such as paleochannels, scours, rider seams, clay veins, or crevasse splay deposits. Fractures, i.e., joints and faults, also contribute to roof falls. The trend, dip angle, and density of fractures, and the presence of slickensides are important in determining roof stability. Stress fields underground, both tectonic and mining-induced, not only can determine whether failure will occur, but also the mode of such failure. Detrimental features of a more localized nature include kettlebottoms, coal balls, and moisture fluctuations. The use of paleoenvironmental studies is important in determining hazardous roof conditions. Particular hazards are moremore » likely to be present in one paleoenvironment than another. When that environment is determined in advance of mining, precautions can be taken during the mine-planning phase.« less