Quantifying the influence of variations in rock mass properties on stope stability

Variations in rock mass properties are well-established in rock mechanics and underground mining. The literature is replete with methods of assessing them and determining values that are used in design or numerical analysis. In this paper, a simplified 3D model is constructed for a tabular orebody in the Canadian Shield and instability is quantified using the ”brittle shear ratio” criterion to calculate the volume at risk. A 1-4-7 stope pillar sequence is implemented on four active levels, and three variations in the properties of the host formation are assessed. It is observed that the locations of ore at risk follow the formations of stope pillars and are then transferred to the sill pillars above and below. Instability in the footwall and the hanging wall is observed to be lesser in volume but remains persistent. With the allocation of weak properties to the host rock, at-risk volumes increase in the orebody, footwall, and hanging wall, and the reverse trend occurs with strong greenstone properties. It is concluded that the stress increase in the orebody is due to transfers from the weaker host rock, while that in the greenstone formation is due to the use of a lower compressive strength value.