The highest safe extraction ratio is the goal of coal mine planning. This may be affected substantially by the interaction of regional in-situ stress with coal-measure discontinuities such as faults, interbedded weak and strong strata, rolls, and sandstone channels. The effect of discontinuities is to interrupt or concentrate the mechanics of stress transfer and cave development during coal extraction, often resulting in a costly change in mining plan. Heavy ground conditions were encountered when extracting pillars during retreat in a room-and-pillar panel at a mine in central Utah, resulting in the decision to bypass about 25% of the coal within the panel.

Conditions which led to abandonment of the central portion of the

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panel were observed in data obtained from instruments installed for subsidence monitoring purposes on the surface, in the overburden, and underground. Instrumentation included strain measurement at the surface and both absolute and relative stress measurement at mine level. Data from tape extensometer readings, overcoring, and borehole pressure cells support a rotated fault-block hypothesis. In the mine area, frequent nearly vertical faults are present and can be located on satellite imagery. Two major faults are present and can be located on satellite imagery. Two major faults striking obliquely across the panel appear to have isolated a block of rock that rotated toward the gob at the north end of the panel as mining progressed, creating adverse loading conditions at mine level. The combination of satellite imagery, ground mapping during mining, and selected instrumentation may hold some potential for improved mine development in areas experiencing similar ground control problems due to the interception of geologic discontinuities.

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