Mine Configuration and Its Relationship to Surface Subsidence

J. L. Craft, T. M. Crandall
1988 Journal American Society of Mining and Reclamation  
Careful evaluation of mine maps has been of considerable aid in understanding subsidence failure mechanisms above active and abandoned underground coal mines. This, in turn, aids the investigator in: (1) predicting what might happen in the future, and (2) designing proper corrective action to prevent additional subsidence events. Factors to be considered include accurate orientation of the mine map with surface features; pillar shape, size, alignment, and strength; percent coal extraction;
more » ... urden thickness and composition; location and orientation of barriers and unmined coal reserves; entry and haulageway size and alignment; water conditions in the mine; geologic structure; the presence of retreat mining in adjacent or nearby panels; and pillar alignment in association with retreated panels, Field investigations, includirtg drilling programs, based on the evaluation of available mine maps have established clear relationships between surface effects of mine subsidence events and specific underground conditions causing the subsidence. These include: (1) coal barriers acting as fulcrum points causing massive surface cracks due to transfer of overburden loads (Graysville and Willow Bend, AL); (2) pillars incapable of supporting overburden loads (Graysville, AL); (3) alignment of' pillars left t·o protect the surface, creating residual stress fields that fail in a catastrophic manner (Fairmont, WV); and (4) natural fracture systems, such as faults and joints, providing conduits for movement of unconsolidated sediments (piping) into the mine void and subsequently, movement of the surface (Arnold, PA and Shinnston, WV), These events have occurred with overburden thickness ranging from 20 ft to over 700 ft, Surface damage ranged from minor cracks and no vertical displacement to vertical displacement of 2,5 ft and cracks up to 6 ft wide and 200 ft deep,
doi:10.21000/jasmr88020373 fatcat:fpmjaeqwyfhzzm7nuadab3i7k4