Dias, E & Holtzhausen, W 2024, 'Change in mining sequence and design methods at the Frog’s Leg underground mine due to high-stress seismic conditions', in P Andrieux & D Cumming-Potvin (eds), Deep Mining 2024: Proceedings of the 10th International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 295-310, https://doi.org/10.36487/ACG_repo/2465_14
(https://papers.acg.uwa.edu.au/p/2465_14_Cordeiro_Dias/)
Abstract: Frog’s Leg underground mine experienced a change in seismic behaviour in August 2017. The increased stress levels resulted from a combination of increased mining depth, mining span, high-stress bursts of barren pillars, stoping abutment, and shear/slip on seismically active structures.
Extraction sequence changed over years to account for variable orebody geometry, geotechnical constrains, recovery and productivity.
Prior to August 2017, seismic behaviour was predominantly triggered by stope firings and the seismic hazard was successfully managed through exclusion zones and re-entry times. From August 2017, the seismic behaviour changed to random events that were not blast related. Stoping in the Mist was suspended following rockburst damage in October 2018. Due to the increased probability of occurrence and likelihood of exposure owing to the inability of the ground support system to effectively control rockbursts, an alternative method that limited/excluded access to the high stress rockburst-prone areas in ore drives was investigated. As a result, the mining strategy in the Mist changed to side access using footwall drive access with crosscuts into the stress shadowed backfilled stopes.
This paper provides an overview of the measures that were implemented to mitigate the hazard associated with increased mining-induced seismicity and increased stress levels.

Keywords: seismicity, high stress, footwall drive, extraction sequence, ground support