International Journal of Mining Engineering, 3:195–213, 1985
Authors: J. F. T. Agapito, and S. J. Mitchell (AAI), and L. A. Weakly (Exxon Company)

Stability in Exxon’s Colony Pilot Mine in the Piceance Creek Basin, Colorado, has been monitored by periodic pillar stress determinations and roof-to-floor convergence measurements since 1971. Pillar failure has caused marginal stability in some areas of the mine. Measurements taken during the process of failure provided valuable information on the in situ pillar strength and long-term behavior of the mine structure. Four pillars were reinforced by 32-mm (1.25-in.) diameter tensioned grouted bolts to increase long-term stability in the northern area of the mine. Stability of this area is necessary because future plans envisage its use as an exit/access and ventilation exhaust. Computer analyses were performed to help evaluate the effect of pillar reinforcement on long-term stability. Results indicate that bolting is particularly useful in stabilizing failed pillars, but its effects are significant only in the immediate area of the pillar. The projected significant decrease in deformation of two extensively failed pillars near a main entry indicates that bolting reinforcement will assist the long-term stability of the opening.

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