Monitoring pillar behaviour while driving towards a shear zone in highly stressed ground at Vale's Creighton mine

摘要

High stress ground conditions within current development at the Creighton Mine, 461 Orebody, 8010 level (2440 m) are exacerbated by stress transfer into this region from the effects of production above in combination with blocky ground conditions, pre-existing structure, and biotitic shear zones on the level. As an opportunity to measure the effect of mine development on a round by round basis, a dense array of instrumentation was installed through what would be a future pillar prior to the adjacent development taking place. Contouring between adjacent multi-point borehole extensometer measurements has provided an excellent depiction of the pillar behaviour as development rounds, using the current face destress procedure, approached a known shear zone. A high displacement trend was revealed across the entirety of the shear that corresponded with a measured displacement jump after each development round, along with concurrent displacement in each previous round. Confidence in the geological mapping of the shear zone is quantified as the depth of brittle failure continued to develop/ extend towards the centre of the pillar and the shear zone appearing to separate the pillar into two distinct solid sections.