Strainburst refers to local small seismic events generating shallow spalling with violent ejection of fragments in an active development heading. This rockburst category may affect worker safety and mine productivity. This paper conducts a preliminary study investigating properties of large-scale geological features, mine operational context, and both aseismic and seismic responses generating strainbursts. Using the LaRonde mine as a case study, key parameters influencing strainburst occurrence and severity are defined and highlighted. The distance to a lithological contact and the orientation of the drift are parameters that affect strainburst potential and severity at LaRonde. The analysed bursts were seismically triggered or self-initiated. The analysed seismic events generating strainbursts had a local magnitude of −0.7 ± 0.5 on average and were located between 3 and 58 meters from the damage. Finally, strainbursts mostly occur within five days after a development blast.
Mining in deep, hard rock mines poses many challenges for engineers. An increasing engineering challenge associated with higher stress conditions at great depths is the potential for strainbursts, which can have considerable adverse effects on mining activities. In this study, strainburst refers to local small seismic events that generate shallow spalling with violent ejection of fragments in an active mine development heading (Ortlepp, 1992).
Many authors have studied and described strainburst mechanisms (Ortlepp, 1992; Ortlepp and Stacey, 1994; Kaiser et al., 1996; Kaiser and Cai, 2013). However, strainburst parameters such as time of occurrence and its link to more remote seismicity are uncertain and not fully understood, leading to difficulties in designing and implementing risk management strategies. Seismic risk management should rely on all available data at the mine to help understand rockmass responses to mining. Seismic and aseismic responses to mining are influenced by many parameters, such as contrasts in rock mass competency and stress conditions, which are partially controlled by the proximity to large-scale geological features such as faults, lithological contacts, and foliation. Hence, it is of great importance to characterize geotechnical environments and both seismic and aseismic responses properly in order to better understand strainburst occurrences.
This paper presents the development of a geotechnical model based on the integration of geological and geomechanical characterization data along with seismic events. This model provides useful tools for understanding the rockmass response to mining. More specifically, this paper focuses on determining seismic parameters and the properties of large-scale geological features that affect strainburst occurrence and severity. Properties of large-scale geological features refer in this case to the distance from the damage to geological contacts and faults, and the angle of interception of the damaged drift with the foliation. Analysis of the seismic sources includes the quantification of the distance from the damage to the linked seismic event, the magnitude of the linked seismic event, and the time of occurrence of the event in relation to the previous blast in the sector.
The study uses strainburst data from the LaRonde mine, a deep seismically-active hard rock underground mine located in the mining district of Abitibi-Témiscamingue, in Quebec, Canada. As mining progressed deeper, this mine experienced an increased frequency of strainbursts, providing a unique opportunity to demonstrate the applicability and usefulness of the developed methodology.