Seismicity at Big Bell mine.

Twelve rockbursts damaged access developments in the Big Bell mine between February 1999 and June 2000, with severe damage extending up to 100 m along footwall drives. A series of precautionary measures was implemented which included extended re-entry periods and exclusion zones in high-risk areas, improved rockburst-resistant support systems in areas prone to damaging seismic activity, and improved support in areas prone to shakedown damage. A portable 8-channel monitoring system was installed as an interim measure in August 1999, with a full-scale system commissioned in February 2000. The objective was to monitor relative seismic activity and determine trends. MAP3D numerical modelling was used to investigate the relationship of seismicity and various stress components in order to assess the relative seismic risk in current and proposed working areas. This information is used to determine where in the mining cycle rockburst-resistant support is needed. Two distinct modes of seismicity have been identified: small-scale localised high-frequency events in high-stress areas, and larger events related to shear along previously intact foliation surfaces. The onset of seismicity, with associated rockbursts, has required changes to be made to stope sequencing, development design, and support and reinforcement systems.
Twelve rockbursts damaged access developments in the Big Bell mine between February 1999 and June 2000, with severe damage extending up to 100 m along footwall drives. A series of precautionary measures was implemented which included extended re-entry periods and exclusion zones in high-risk areas, improved rockburst-resistant support systems in areas prone to damaging seismic activity, and improved support in areas prone to shakedown damage. A portable 8-channel monitoring system was installed as an interim measure in August 1999, with a full-scale system commissioned in February 2000. The objective was to monitor relative seismic activity and determine trends. MAP3D numerical modelling was used to investigate the relationship of seismicity and various stress components in order to assess the relative seismic risk in current and proposed working areas. This information is used to determine where in the mining cycle rockburst-resistant support is needed. Two distinct modes of seismicity have been identified: small-scale localised high-frequency events in high-stress areas, and larger events related to shear along previously intact foliation surfaces. The onset of seismicity, with associated rockbursts, has required changes to be made to stope sequencing, development design, and support and reinforcement systems.