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Itasca has been working with AngloGold Ashanti in South Africa to understand rock behavior, especially brittle failure mechanisms, inherent in deep gold mines in South Africa. The ultimate goal of this work is to develop a rational methodology for mine design, especially as mining continues deeper. Itasca is doing this by developing a generic mechanical model for rock behavior around advancing stopes in deep gold mines that can reproduce the induced fracture patterns. The work will allow fracturing mechanisms to be explored, and then relate them to in-situ conditions such as parting planes, in-situ stresses and existing mining geometry. Two approaches have been employed to develop a modeling environment for stope-scale systems. The first approach is continuum-based and utilizes the Mohr-Coulomb strain softening model using FLAC alone. The second approach employs a coupled continuum-discontinuum technique, where the continuum region is modeled by FLAC and the discontinuum region is modeled by a PFC2D model embedded within a larger FLAC model.
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Both investigated approaches produce well-defined shear fractures and stope-parallel extension fractures similar to those observed in the field. In the coupled FLAC-PFC2D models, the bonded-particle material exhibits formation of conjugate shear fractures that correspond with shear fractures in the continuum material. Additional damage structures appear to be present within these shear fractures — e.g., en echelon fracturing in the bonded-particle material is similar to what is observed in actual shear fractures underground. There is also evidence of spalling at the stope face, distributed damage ahead of the stope face and formation of extension fractures. Therefore, the coupled model successfully exhibits a richness of localized detail in the simulated damage, while the surrounding FLAC grid provides for large-scale models to be implemented.
Brummer, R.K., and A.J. Rorke. (1984) “Mining Induced Fracturing Around Deep Gold Mine Stopes,” COMRO, unpublished research report 38/84, project GR3FO1, July.
Katsaga, T., and D. O. Potyondy. “A Generic Stope Model for Investigation of Fracturing Mechanisms in Deep Gold Mines,” paper ARMA 12-541 in Proceedings of 46th U.S. Rock Mechanics/Geomechanics Symposium, Chicago, USA, 24–27 June 2012.
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