Rock burst observations from hard rock mines: Failures, successes, lessons learned

Rock bursting is a complex mining induced phenomenon that is difficult to capture in precise mathematical terms. In particular geological conditions that contribute to rock bursting are difficult to quantify: faults, intact rock properties, and other rock mass conditions are difficult to quantify and vary, sometimes within small distance. Stress levels that store energy or drive structures can also be complex. Geological structures can channel stress between the void and the discontinuity and/or alter the local stress direction. Rockmass strength or stress variations may change behaviour, from strain softening/rock degradation to strain energy storing and eventual violent failure. Where data gaps exist, or there is insufficient understanding to derive a precise analytical or numerical solution, empirical methods are often used. Empirical design tools operate on observational data, or more simply practitioners may just use a trial and error approach. This requires good records and quality data. Given the potential severity of rockbursting in deep underground mines, there may not be the luxury of waiting to see how well mine designs and/or support systems work. Sharing observational data can be difficult due to a reluctance to advertise failures. This paper use examples from relatively high stressed hard rock mines, to highlight some of the complex issues that are part of the rockbursting problem. The main focus is on ground support performance, however it is recognized that a multi-tiered risk mitigation approach should be employed for rockbursting conditions.