Preventing Massive Pillar Collapses in Coal Mines

A massive pillar collapse occurs when undersized pillars fail and rapidly shed their load to adjacent pillars, which in turn fail. The consequences of these chain-reaction failures can be catastrophic. One effect of a massive pillar collapse can be a powerful, destructive, and potentially hazardous airblast. Thirteen recent massive pillar collapses have been documented in West Virginia, Ohio, Utah, and Colorado. Data collected at the failure sites indicate that all of the massive collapses occurred where the pillar width-to-height (w/h) ratio was 3.0 or less and where the Analysis of Retreat Mining Pillar Stability Factor was less than 1.5. The unique structural characteristics of these pillar systems apparently result in sudden, massive pillar failures, rather than the more common slow “squeezes. The field data, combined with theoretical analysis, provide the basis for two partial-extraction design approaches to control massive pillar collapses. These are the containment approach and the prevention approach; practical examples are provided of each.

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