Authors: Smith-Boughner,LT; Urbancic, TI; Baig, AM

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Smith-Boughner,LT, Urbancic, TI & Baig, AM 2017, 'Resolving sill pillar stress behaviour associated with blasts and rockbursts', in J Wesseloo (ed.), Deep Mining 2017: Proceedings of the Eighth International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 257-267,

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In this paper, we describe the seismicity associated with the excavation of a stope inside a sill pillar in a North American hard rock mine. By taking a continuum approach to describing the microseismicity, we reconstruct the deformation state of the rock mass during production and production. Microseismic events are generated through dynamic changes to the stress in the rock mass. While an individual microseismic event corresponds to slip on a discrete surface, the combined deformation of a group of events results in a collective behaviour. The combined deformation is quantified using a dynamic parameter representation and allows us to gain additional insight into the behaviour of the rock mass through incorporation of stress and energy release, and spatio-temporal relationships of observed seismicity. It provides a quantitative framework for relating changes in the intensity, concentration and rate of seismicity to changes in the rock mass. In this paper, we show that the bulk of an elastic deformation, for the most part, follows spatially around the major blast locations. Using these tools and seismic moment tensor data for these events, we track changes in the strength of the rock mass in the hours and days following the blasting of a stope. The stresses in the stope are relieved through the excavation and shed to the surrounding rock mass. The timing and mechanism for this stress transfer varies near faults or close to other structural boundaries. Depending on the nature of the interface, the change in the collective behaviour could be a change in the event rate, inter-event distance or energy release of the observed seismicity. Based on our observations, we suggest that the application of dynamic parameters to characterise the seismicity associated with mine design can be used to better characterise the stress state, fracture state and deformation state/evolution of a rock mass.

Keywords: microseismicity, rock mass characterisation, stress

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