Reinforcement of Large Pillars by Bolting

Rock Mechanics Productivity and Protection, 25th U.S. Symposium on Rock Mechanics, Evanston, Illinois, March 1984
Authors: S. J. Mitchell and J. F. T. Agapito (AAI), and L. A. Weakly (Exxon Company, U.S.A.)

An analysis of bolting reinforcement of several large [approximately 18-m (60-ft) cube] pillars was performed. The many overcoring stress profiles in pillars at the mine were used to produce generalized stress distributions at various stages in pre- and post-failure. A complete stress-deformation curve was estimated from this data. The effect of pillar bolting on the load-deformation behavior was extrapolated from the observed unbolted behavior. Bolting can increase pillar strength by up to 10 percent. The effect of bolting on general mine stability was examined with a short computer analysis. The computer model was calibrated against measurements performed at the mine, and produced good agreement between measured and modeled stresses. The analysis indicated that bolting increases the bolted pillar safety factors in the event of additional pillar failure by a small amount (approximately 5 percent). Progressive pillar failure is unlikely, because arching transfers most load from yielding pillars to large unmined abutments rather than to the smaller panel pillars.

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