Analysis of microseismic cluster locations based on the evolution of mining-induced stresses

Authors: Shnorhokian, S; Mitri, HS; Moreau-Verlaan, L Download Paper

DOI https://doi.org/10.36487/ACG_rep/1410_51_Shnorhokian

Cite As:
Shnorhokian, S, Mitri, HS & Moreau-Verlaan, L 2014, 'Analysis of microseismic cluster locations based on the evolution of mining-induced stresses', in M Hudyma & Y Potvin (eds), Deep Mining 2014: Proceedings of the Seventh International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 709-722, https://doi.org/10.36487/ACG_rep/1410_51_Shnorhokian



Abstract:
Numerical modelling is increasingly being used in the mining industry as part of the planning process. Its areas of application range from the estimation of in situ stresses at planned locations of underground facilities, to the effects of stope sequence alternatives on drift instability. In terms of the size of their study area, numerical models can range from a section of a given level to mine-wide dimensions, with an increase in complexity and input information requirements. Microseismic activities induced by mining operations can be studied using mine-wide numerical models that have been properly calibrated. In this paper,mining-induced seismicity at the Vale Garson Mine is examined between 2006 and 2008 with a numerical model constructed in FLAC3D. Two sets of microseismic activities are used as a basis of the study; events from the microseismic database with energy outputs greater than 100 kJ, and events that have resulted in rockbursts within developments, regardless of their energy outputs, for a total of 24 events. In the first phase of the study, the coordinates and location error of each event, as obtained from the microseismic database, are used to construct a location cube defining the maximum boundaries within which the actual coordinates must lie. Based on the 24 location cubes plotted, four microseismic clusters are identified. In the second phase, the mine-wide model is calibrated based on laboratory results of rock samples, borehole data of rock mass properties, and an in situ stress measurement point on 4900L (1,495 m). The historical stope sequence followed at the mine is replicated in the model from 2001 to 2008. Mining-induced stresses within the location cubes of two clusters are examined using the maximum shear stress, brittle shear ratio, and the continuous change in differential stress (CC-DS) when compared to pre-mining conditions. It is shown that all event location cubes studied register an abrupt increase in CC-DS some time before or during the occurrence of that event. In the final phase, the most microseismically active zone in one of the geological units is compared to relatively quiet zones in terms of CC-DS conditions. It is shown that theCC-DS values are mostly constant in the latter zone, while they typically undergo abrupt and sudden changes in the active one prior to microseismic events. Hence, a new method of analysis with the potential of predicting the location of microseismic clusters is introduced.

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