The effects of in situ stress uncertainties on the assessment of open stope stability: Case study at the Niobec Mine, Quebec (Canada)

In deep underground mines, a successful development plan to exploit deeper mining levels is highly dependent on adequate consideration of the magnitude and orientation of situ stress state. However, significant uncertainties are associated with the estimation of these parameters. The in-situ stress values that are used in the evaluation of the stability of underground structures in each mine strongly depends on the results of measurement of the stresses as function of the mine depth and the methodology used for the interpretation of the data as well as engineering judgment. These interpretations could produce several scenarios for estimating the stresses in a mine. Each scenario could yield different stability assessment results some of which were not normally used in the current mine stability study. Three different scenarios for estimating stress at the Niobec underground mine (Quebec, Canada) were determined based on the data available from previous stress measurement campaigns. Numerical modeling (FLAC3D) was used to evaluate the potential of brittle, tensile and compressive failure for the vertical transverse and rib pillars. The results demonstrate that in spite of the development of extensive brittle and tensile damage zones within the rock mass, no major brittle or tensile failure is expected to occur at the considered mining levels based on all three stress scenarios. Moreover, meaningful differences in the stability analysis results between the three stress scenarios highlight the importance of appropriate selection of stress estimation approaches in planning deeper mine levels.