Predicting rock failure around boreholes and drives adjacent to stopes in Indian mines in high stress regions

During stoping in a high rock stress regime, the failure of production drillholes and drives through breakouts poses serious problems in terms of the deployment of men and machinery, and threatens the very continuance of the particular stoping method. In order to continue extraction, it becomes imperative to study the behaviour of the breakouts in the field (as laboratory investigations cannot be directly applied to the field) so that breakout can be predicted well in advance and the necessary corrective measures can be taken as appropriate. For this purpose, the failure of production drillholes and the drives were investigated during sublevel open stoping at the Zawar Group of mines in India.Three distinct stages of the breakout were identified. Analysis of these led to formulation of the empirical models, correlating the depth of the notch of breakout with rise in the field stress. Knowing the field stress, the extent of breakout of these openings can be predicted; alternatively, by using these models, the prevailing ground stress can be estimated by back analysis. The latter, however, is more useful in calibrating numerical models. The breakout of boreholes has also been used to define the limit of application of various stoping methods suitable for steeply dipping orebodies.