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Longwall pillar design--some recent developments.

Soc Min Eng AIME Preprint 89--103 1989; :1-9
Effective ground control in the gate entries, particularly in the tailgate travelways, is essential for safe longwall mining. Longwall pillars maintain gate entry stability and carry abutment loads. To answer the need for effective longwall pillar design, an empirical method called analysis of longwall pillar stability (alps) was proposed several years ago. Some recent research at the U.S. Bureau of Mines has focused on the refinement and verification of the alps method. Alps was originally developed from field studies in which multiple stressmeters were installed in longwall pillars and monitored during mining. Several new field studies have now been incorporated into the alps data base. The field measurements have been used to verify formulas for predicting abutment strength and pillar loads, and to develop an expression for the distribution of the abutment load. Since its development, the alps method has been applied to nearly 100 mining case histories from longwalls located throughout the eastern United States. Back-analysis of "stability factors" for these case histories indicates that alps is applicable to a wide variety of mining situations. In its present form alps is most useful for preliminary longwall pillar design, and for optimizing pillar size based on site-specific experience. A computer program is being prepared that will make alps even more accessible to mine planners. Future Bureau research will incorporate alps into a complete gate entry design package, which will address entry support and roof and floor rock properties as well as pillar design.
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OP 93-89
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Society of Mining Engineering AIME Preprint 89--103