| Concern about the cause and potential effects of microseismicity has been rising in the mining industry over the last few years. Seismic events can have a tremendous effect on the physical integrity of mine openings, production and safety of mine workers or any combination of these. While the majority of seismic events have no immediate impact on mining, as mining reaches greater depths, with increased extraction ratios and rates, there is a growing need to understand the interaction between extraction and its effect on the surrounding rock mass. One assumption at Creighton Mine, INCO Ltd., whose data is used in this case study, has been that large scale geological features, such as faults, are the main source of microseismic activity. The argument presented in this study is that the majority of seismicity is associated to the failure of small scale features, and is the result of failure of the rock mass following a critical path through the joint fabric under the constraints of the induced stress regime.; The data in this study is drawn from the 4500 vertical retreat mining (VRM) block. The microseismic events associated with the mining of this block were recorded with an Electrolab MP-250 system, which records the arrival times of events at the sensors and their locations. A multivariate statistical technique, the Principal Components Analysis (PCA), has been used to analyse the spatial distribution of events in a cluster and to determine the orientation and direction of failure planes. These planes are then compared to geological structures and joint sets defined by mapping. Using linear elastic boundary element modelling, the normal and shear stresses on the planes have been calculated at the event locations using a ubiquitous joint analysis. The planes are then compared to one another to identify the most probable plane to fail. |
