New research data suggests that it is time to re-think standing assumptions made when assessing rockburst damage and by implication when designing support in burst-prone ground.
A critical assessment of the current mine support design guiding principles led to the conclusion that the primary damage mechanism to an excavation site is often a seismically triggered strainburst or self-initiated strainburst and damage is often not rooted in momentum or dynamic shaking from a remote source. For example at the Jinping II tunnel in China, over 500 strainbursts were encountered without any triggering earthquakes or fault slip events. As a result, rockburst damage is primarily related to the state of stress and the local mine stiffness at the potential damage location and only indirectly related to the seismic ground motion. A reliable means of identification of mining induced strainburst potential will lessen vulnerability of an excavation. Further, once strainburst potential is identified, failure may then be mitigated by using methods of hydraulic fracturing that allow for the creation of fracture networks, thereby damaging the rockmass prior to mechanical excavation.
INNOVATION IN PROGRESS
Research is underway to build a strainburst database with related excavation vulnerability assessment parameters and a methodology to assess deformation potential as a strainburst trigger is under development. Forensic analysis to review the damage to an excavation or its support will aid in better understanding the cause of failure and necessary design parameters. The BurstSupport Tool‒ created through earlier related research projects‒ will then be updated to assist in strainburst support analysis. Related step-change innovations are being explored to overcome existing deficiencies of hydraulic fracturing technology, namely the use of stimulation and solids injection for application in mining. It is anticipated that the results will also find application in the oil and gas sectors. Two keynote industry lectures by P. K. Kaiser at Support’13 in Perth, Australia, and at Rasim8 (rockburst and seismicity in mines) in Russia (2013) address the need to re-think standing assumptions made when assessing rockburst damage and by implication when designing support in burst-prone ground.
- Peter Kaiser, CEMI, RTC-UMC
- Ming Cai, MIRARCO
- Simon Nickson, Vale
- Sami Talu, Rio Tinto
- Claire McAneney , NSERC