Mining Front Stability Assessment Using Diametrical Core Deformation Analysis And Numerical Modelling
Sponsor: Natural Resources Canada, Newmont, Ministry of Economics and Innovation of Quebec
PhD Thesis, Yizhuo Li
Regularly estimating mining-induced stress is crucial due to variations in stress depending on many factors like depth, proximity to geological structures, and the history, geometry, and orientation of excavations with respect to principal in-situ stresses. As mining operations progress, the stresses near drifts, ramps, and sill drives continually change. These dynamic changes can significantly impact mining stability, potentially leading to various forms of rock failure. Mature in-situ stress measurement techniques are not well-suited for this task because of their high cost and time-consuming, typically conducted only a few times throughout the lifespan of a mining project. Consequently, there arises a need for a simple and practical technique that can provide rapid stress information. The use of a core-based stress estimation method is considered to have potential, as it can be frequently implemented at the mine site with only on-site sample collection required.
This study focuses on the development of near field stress estimation technique using the rock cores. Specifically, local stress field is predicted through the diametrical core deformation. The thesis begins with a comprehensive review of the underground stress measurement methods, along with the discussion of their merits and limitations. The review suggests that the diametrical core deformation analysis is superior to other methods. Following the literature review, a laboratory test system for measuring core diametrical deformation is developed. The test apparatus is designed to continuously measure the core diameters in 360 degrees for the most common sizes of exploration rock cores. Rock cores from two case study mines were used to determine differential stresses using this developed system. It reveals the feasibility of designed measuring system and application of diametrical core deformation analysis in hard rock mines.
A new analytical model is developed based on the core deformation analysis, enabling the determination of planar major and minor principal stresses near the mining front. Verification of the developed analytical model is done by comparison with reported laboratory experiment results, showing good alignment between the estimated stress from the analytical model and the actual applied stress in the laboratory experiments.
The analytical model is then extended to practical applications. The diametrical core deformation technique (DCDT) is applied to an operating gold mine. The near field stresses are estimated and serve for the validation of DCDT through previous field measurements and numerical modelling. Finally, the demonstration of DCDT in practice for local stress field predication and mining front stability assessment is carried out at another underground gold mine using laboratory measurement of extracted rock core and numerical modelling of the local area of the field experiment.