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CMRR aids in longwall gate entry design: a database analysis may help longwall designers.
Mark-C; Chase-F; Molin-G
Coal 1994 Feb; 99(2):40-42
For practical design, the most significant conclusions from the study are: 1. the three elements determining performance are pillar size, entry width and primary support, and, 2. gate entry design must be based on roof quality. The first step is to evaluate roof conditions. If underground exposures are available, the CMRR may be determined directly. In most in stances, it is probably sufficient to place the mine roof into one of the three categories described earlier- strong roof (CMRR > 65), moderate roof (45< CMRR < 65) or weak roof (CMRR < 45). The next step is to use ALPS-SF to determine the pillar size. With the CMRR, the proper ALPS-SF can be obtained using the design equation given above. For weak roof, an ALPSSF of 1.3 seems appropriate, while in strong roof an ALPS-SF of 0.7 should perform adequately. Pillar widths are then selected so that the design achieves the proper ALPS-SF. Finally, the entry width and the primary support may be estimated from what has been successful in the past. In weak roof, it appears that the entry width should be less than 18 ft. Longer bolts, typically at least 6 ft, also seem appropriate in weak roof to achieve a Primary Support Rating of 0.25. In strong roof, entries of 20 ft and a Primary Support Rating of 0.15 appear to be adequate. While the study was not successful in defining the necessary secondary support, the indications are that if the other criteria are met, no more than a moderate level of cribbing should be necessary.
Mining-industry; Underground-mining; Engineering-controls; Control-technology; Ground-control; Ground-stability; Computer-software; Computer-models
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Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division