ABSTRACT:

The occurrence of floor heave, as mining depths increase over time, is a growing problem in the United States and abroad. A central Appalachian longwall mine operating in the Pocahontas No. 3 seam in Southwestern Virginia recently encountered excessive floor heave in the main entries after adjacent longwall panels were extracted. This occurred in an area with an increased thickness of fireclay in the floor, combined with a significant change in entry orientation. In this paper, a numerical modeling approach using calibrated large-scale and detailed small-scale models is presented. The detailed model was calibrated to site-specific field observations in the mine and used to explore how the strength of the floor material and the orientation of the horizontal stress affect the development and extent of floor heave in the model. Both numerical modeling and geologic mapping suggest that both the strength and thickness of the floor material as well as the horizontal stress field play a significant role in controlling floor heave. This understanding, combined with quality geologic exploration and rock mechanics data, can be used to aid engineers in safely designing mines to mitigate the challenges associated with excessive floor heave.

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