Investigation into Coal Pillar Stability Affected by Mining Induced Stress Development within Different Coal Pillar Widths in Deep Mining

Understanding and mastering the evolving patterns of mining induced stress (MIS) is the key to control and utilize the action of rock pressure in deep underground mining, especially for designing safe and economic coal pillar widths in longwall mining. The various widths of coal pillars result in differences in deformation, stress and movement of rocks surrounding the gateway and thus strongly influence the stability of coal pillar and maintenance of the gateway. Based on observation and numerical simulation, the characteristics of MIS and the stability of both coal pillar and gateway were synthetically investigated. The results show that the stress distribution laws and deformation characteristics of rocks surrounding gateway are obviously diverse within different widths of coal pillars during caving. Along with the variety of widths of pillars, stress distribution between coal pillar and coal entity could be switched. The deformation and the stability of gateway are determined by the stress distribution and its development of both coal entity and coal pillar. The appropriate width of coal pillar should be designed less than the critical width switched from the coal entity to coal pillar. And the calculating formula of reasonable width of coal pillar is gained. Engineering practice show that research findings provide some theoretical basis for the rational setting of the coal pillar width, the layout, support and maintenance of gateway, the stability control of the rock surrounding gateway and the safe and economic production etc.