Estimation of Coal Pillar Strength by Finite Difference Model

Longwall mining is now predominately used in coal mines where somewhat difficult conditions exist. As in the case of all other underground mining methods, pillars are integral parts of the mining design. The choice of shape and dimensions of the pillars has significant impact on the recovery and hence on overall productivity of the mine. The process of pillar design in longwall mining entails the selection of a safety factor, which is done by estimating the magnitude of the load applied on the pillar and the load bearing capacity of such pillars. In this paper, finite difference modeling principles have been applied to a typical coal pillar. The pillar strength is then estimated with various width/height ratios. These results have been compared with the results obtained from the conventional methods of pillar design. The effect of roof and floor quality on the strength of the typical pillar has also been evaluated in the same manner. It is concluded that although the finite difference method is not always the perfect method for such estimation, but the results clearly demonstrate that it produces more acceptable design than the conventional method, especially under undesirable conditions regarding the interface between pillars, roof and floor. An additional advantage of such method is shown to be its capability of being applied in situations where complex parameters prevail