Optimum design of rib pillars in a longwall mine -A threedimensional numerical modelling

Abstract

The present paper deals with the design of optimum width of rib pillar of the longwall retreat coal mine based on three-dimensional finite element method. A case study of a typical longwall panel has been taken. Optimum width of rib pillar was determined at varying depths under similar geo-mining conditions of the typical panel. Physico-mechanical properties of the coal and other rocks are assumed tobe linearly elastic, isotropic and homogeneous. Six models of different width were simulated at varying depths. The results in terms of stresses as well as factor of safety were obtained. Based on the results of factor of safety, yield percentages at factor of safety 1 and 1.3 of rib pillars were determined. Yield ratio (ratio of yield percentage at factor of safety > 1.3 and yield percentage at factorofsafety <1) was also calculated for rib pillar. Just stable condition for particular width of rib pillar is obtained at yield ratio of 5. Further, for consideration of additional factor of safety, optimum width was taken 1.5 times the calculated width of rib pillar (at yield ratio of 5).