Assessment of Coal Pillar Strength under the Influence of Multilayer Weak Bedding Planes Employing Analytical and Numerical Simulation Studies

Abstract

Efficient coal extraction from underground mines is largely dependent on the stability of coal pillars, especially in the presence of geological discontinuities that weaken their strength. In Indian coalfields, traditional empirical formulas for pillar strength often neglect these discontinuities, focusing instead on pillar dimensions and coal strength. This study employs numerical simulations to evaluate the impact of multilayer weak bedding planes, placed at various positions within the pillar, on its strength. Initially, single-layer weak beds with thicknesses between 0.2 m to 0.5 m were modeled at different positions (roof-interface, middle, and floor-interface) of the pillar, showing significant strength reductions, particularly at the roof interface. Expanding the study to multilayer weak beds (up to five layers) with varying thicknesses further demonstrated that both the number and position of these beds critically influence pillar strength. The results underscore the necessity of accounting for geological discontinuities when designing coal pillars, as their presence can substantially reduce loadbearing capacity and compromise mine safety.