10 / 2023-05-10 23:51:54

Mining front stability assessment in hard rock mining – A case study

underground mining,rock mechanics,mine stability,diametrical core deformation,biaxial strength,numerical modelling

As mines go deeper, higher in-situ stress is encountered, as well as the stress near mining faces. Mining-induced stresses at a mining front are the principal stresses in the plane parallel to the front. These stresses can initiate face failure by triggering different failure mechanisms, such as spalling, slabbing, burst, bulking and out-of-plane shear failure. In deep mining, mining-induced planar stresses could cause immediate failure, even rock burst during mining especially in brittle rock (Yun et al., 2010). Therefore, it is essential to regularly assess mining front stability by estimating mining-induced planar stress distribution.

This research demonstrates a practical assessment of mining front stability using combined approaches, including diametrical core deformation technique (DCDT), biaxial strength failure criterion and numerical modelling. The study adopts the failure criterion under the biaxial stress state to conduct the stability analysis, which is established by Yun et al. (2010) by investigating the biaxial compressive strength of different types of rocks. This criterion considers the major principal stress () in the plane parallel to the free face, the intermediate principal stress (), and the uniaxial compressive strength of intact rock (). Such that, knowledge of near-front mining-induced planar stresses is required. Estimating mining-induced stress is a challenge in practice as it changes with mining activities and is influenced by the size, shape, and orientation of excavations. The authors have recently developed a simple and practical technique to determine the mining-induced stress based on the diametrical core deformation (Li and Mitri, 2023). The basis of DCDT is to use strain relief of the rock core to estimate the induced stress at the point where the rock core is extracted. Such relief can be captured in the laboratory from the diametrical deformations of the rock sample using a customized measuring system (Li and Mitri, 2022).



Numerical modelling is used to simulate a near drift condition in the case study of the Young-Davidson (YD) mine in Northern Ontario, Canada. In this case study, a rock core was retrieved from the front of a drift on 9130 level (1170 m depth). A piece of intact rock obtained at 1.5m from the face is used to conduct DCDT for the determination of principal stresses, both magnitude and orientation. Then, the results of DCDT are used as input in the numerical modelling to carry out an iterative calibration process for near-field stresses to obtain a complete stress distribution over the mining front. The biaxial strength failure criterion is then implemented into the numerical modelling for the completion of stability analysis. This research should prove effective and useful for assessing the stability around openings in underground mining, as it combines field measurement, empirical analysis, and numerical simulation.