In underground coal mining, failure is expected to occur at pillar edges as areas are mined out and stresses redistribute. Depending on the post peak behavior of the coal and the local mine stiffness, the mode of failure can be either stable or unstable. In this study, a mechanically coupled numerical model is used to simulate a realistic mining process as experienced in underground coal mining. A discrete element model with softening contact behavior in PFC2D is used to simulate the coal seam, while an elastic continuum in FLAC2D is used to simulate the inner coal and mine roof and floor. In situ stresses are installed and a tabular excavation is widened to induce pillar edge failure. A series of PFC2D model behaviors, called stability indicators, are used to analyze the resulting failure. The stability indicators used here are the work performed by the damping mechanism, the kinetic energy, and the mean unbalanced force. The analysis demonstrates that the stability indicators are able to distinguish between stable and unstable failure. Also, the spatial distribution of damping work and contact softening shows the co-occurrence of model instability and damage.

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