32nd U.S. Symposium on Rock Mechanics, Norman, Oklahoma, 10–12 July 1991
Authors: H. Maleki (AAI) and A. Weaver (Energy Fuel, Southfield Mine)

This paper presents the results of stress measurements, underground observations, and stability monitoring in a southern Colorado mine. The objective of the program was to assess the causes for panel stability problems and to develop a mine layout design to improve ground conditions. This geotechnical program was implemented in cooperation with the U.S. Bureau of Mines (USBM). It consisted of laboratory mechanical property testing, overcoring stress determination at two sites, underground observations/convergence monitoring at problem areas, and numerical modeling for back analyses of stability problems and for development of improved mine design. Stability problems were shown to have been caused by (1) variability in rock mass strength due to the depositional environment of the seam and development of finely laminated rock strata; (2) in situ anisotropic horizontal stresses exceeding bedding plane strength of coal measure rocks, contributing to time-dependent delamination failure; and (3) time-dependent failure in the mine floor, reducing pillar effectiveness and resulting in a chain-type reaction. An improved mine layout design was developed consisting of (1) panel orientation, (2) pillar design, and (3) support design.

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