High stress gradient, critical factor affecting rock burst in the United States mines

Abstract

To enhance the understanding of seismicity and violent failure mechanics for development of control measures, significant research has been dedicated in South Africa, Europe, USA, China and Australia within the last century. Considering complexity of coal pillar mechanics, the author has used two approaches for enhancing understanding of violent failure in US mines (1) carefully reviewing field measurements from US mines and (2) applying a hybrid statistical-analytical method for identifying critical factors contributing to violent failure of coal measure rocks. These studies reinforce the significance of higher risks where mining in areas of high stress gradients, increasing the potential for sudden failure of near seam strata, depending on geologic and stress conditions. High stress gradient condition is commonly found while mining adjacent to some geologic structures (faults/grabens), multiple seam solid-gob crossings and even occasionally on development where failure of highly stressed roof/floor units triggers seismicity and the failure of marginally stable pillar ribs. The latter mechanism has also been experienced in hard rock mines and shown to be associated with buckling failure. Example of stress conditions from case studies are analyzed in this paper.