Stability analysis of the proposed hybrid method of partial extraction for underground coal mining

The hybrid method of partial extraction from underground coal mines has been proposed for better recovery without endangering the surface features. The concept of panel stability, rather than pillar stability, has been suggested for stability analysis of proposed method of partial extraction. The methodology for assessing the panel stability is based on Salamon stability criterion along with pillar stability. It has been outlined as: factor of safety should be more than two for larger pillars, and more than one for smaller pillars; panel factor of safety should be preferably more than two. Panel factor of safety, KLMS/KC, is defined as a ratio of local mine stiffness, KLMS, and post failure stiffness of the split coal pillars, KC. A worst-case scenario analysis has also been suggested as a part of stability analysis by considering failure of split pillars. A typical case study of bord and pillar system of mining has been chosen to evaluate the applicability of proposed hybrid method of partial extraction. It has a major sub-surface feature of perennial stream. There are several pillars underlying this feature. Two variations of hybrid method with galleries width of 7.0 m, 8.0 m and 9.0 m have been taken. It has been concluded from the analysis that by adopting the hybrid method of partial extraction, coal production could be improved substantially without compromising the stability of the surface and underground structure.

► A hybrid method of partial extraction of coal seam is proposed.
► Two criteria for stability analysis i.e. pillars as well as panel stability.
► Worst scenario is also analyzed by considering failure of the smaller pillars.
► Proposed method is found most suitable in the preset case study.