17th Conference on Ground Control in Mining, Morgantown, West Virginia, 4–6 August 1998
Authors: A. M. Richardson, L. J. Gilbride, and J. F. T. Agapito (AAI)

Periodic weighting of longwall supports occurs during retreat of the face under certain geologic conditions. Strong strata in the immediate and main roof tend to cantilever over the gob, weighting the supports periodically. The distance between weighting peaks, as well as the intensity of periodic weighting, is determined by the strength and thickness of roof members, their location relative to the seam, the frequency of jointing, and characteristics of the gob. In this paper the effects of varying several of these variables are investigated using block modeling. The models are calibrated against a published case history of periodic weighting in the Pittsburgh Seam. It is concluded that block modeling is a useful tool for correlating measured support pressure histories with expected modes of strata behavior in the roof, with potential for predicting shield behavior in new geologic environments.

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