Modeling the behavior of a coal pillar rib using Bonded Block Models with emphasis on ground-support interaction

Abstract

Rib spalling is a major hazard in the mining industry and in absence of coal rib support guidelines, accidents have continued to occur in recent years. Developing effective support guidelines requires a complete understanding of pillar damage mechanisms as well as the rock-support interaction mechanism. Bonded Block Models (BBMs) represent a convenient tool for this purpose, as they can reproduce the rock fracturing process reasonably well, but it is not known whether this modeling technique can quantitatively replicate the impact of reinforcement (bolts) on otherwise unsupported ground. To bridge this gap in research, we employed the BBM approach to simulate the behavior of a supported coal pillar rib located in a longwall mine in Australia. This case study presents a unique opportunity in that two otherwise identical chain pillars with different support densities adjacent to one another were instrumented. After calibrating a model against displacement and stress measurements made over the course of mining in one pillar, the support in the calibrated BBM was modified to match that of the adjacent chain pillar. This model could predict the rib displacement to within 6 mm of what was measured in-situ. Given the ability of the BBM to match field-measured displacements and stresses and also field observations for varying support densities, it seems that such a model has the potential to aid in the development of a support design tool. Lastly, the effect of block shape was investigated by replacing the elongated blocks with isotropic polygonal blocks. This model could not reproduce the ground-support interaction very well, likely due to the inaccurate geometric representation of an anisotropic rock like coal.