ABSTRACT
There are two main techniques in coal mining: in the room and pillar method, the coal is extracted in rooms, usually in a regular geometrical pattern and sufficient coal is left in pillars to support the roof; in longwall coal mining, the coal is removed in a long strip, the longwall, which advances forward in a direction perpendicular to the strip, leaving the superimcumbent strata to collapse, or cave, behind it. The way in which this collapse of the overlying strata occurs is not straightforwardbecause of the vagaries in the overburden rock structure, the complexity of the stress redistribution, and the deformation and non-linear characteristics due to failure. Consequently, research into this rock failure process is one of the most active and challenging research activities.
