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Application of the Coal Mine Roof Rating (CMRR) to Extended Cuts.

Mark C
Society for Mining, Metallurgy, and Exploration Annual Meeting, 1998 Mar, 1-7
Since it was first introduced, the Coal Mine Roof Rating (CMRR) has been widely accepted as a tool for geologic characterization and mine planning. This paper discusses the application of the CMRR to another practical ground control problem. Extended cuts (cuts greater than 6 m (20 ft) in length) are commonly used with remote control continuous miners. Extended cuts can greatly increase productivity, but they have been associated with a number of fatal roof fall accidents. When extended cuts are attempted in weak roof, the roof may collapse before it can be bolted, causing hazardous conditions. Until now, it has not been possible to predict where conditions may not be suitable for extended cuts. In this study, data on the CMRR and extended cut experience were collected at 36 mines in 7 states. It was found that when the CMRR was greater than 55, deep cuts were routine in nearly every case. When the CMRR was less than 37, extended cuts were almost never taken. Between 38 and 55, extended cuts were feasible sometimes but not others. The data also shows that extended cuts are less likely to be stable if either the entry span or the depth of cover increases.
Underground-mining; Mining-industry; Mine-safety; Coal-mining; Ground-control; Rock-falls
National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236
Publication Date
Document Type
Conference/Symposia Proceedings
Fiscal Year
NIOSH Division
Priority Area
Other Occupational Concerns;
Source Name
Society for Mining, Metallurgy, and Exploration Annual Meeting, Preprint 98-190
Page last reviewed: November 12, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division