Numerical modelling of the effect of temperature variation on stope stability in Bushveld Igneous Complex
G.O. Oniyide1,2, M.A. Idris2,3
1University of the Witwatersrand, Johannesburg, South Africa
2Federal University of Technology Akure, Akure, Nigeria
3Luleå University of Technology, Luleå, Sweden
Min. miner. depos. 2019, 13(2):121-131
https://doi.org/10.33271/mining13.02.121
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ABSTRACT
Purpose. This paper presents the result of the research carried out on the effect of increasing temperature and stres-ses with depth of mining on the stability of stope within the Bushveld Igneous Complex (BIC), where the South African Platinum mines are located.
Methods. The stability of stope at the platinum mine was analysed using numerical modelling. A commercial geotechnical software, FLAC (Fast Lagrangian Analysis of Continua), was used for the numerical modelling to study and to understand the behaviour of the rock in the deep and hot underground excavations. The modelling is hypothe-tical in the sense that there are no direct field measurements of failure or displacements. However, some field data received from the mines include virgin rock temperature, in-situ stress data.
Findings. The plots of the yielded zones of the model for excavations at the depths of 1073, 2835 and 5038 m revealed that there would be shear and tensile failures at 2835 and 5038 m, however, these failures will be higher at 5038 m than what will be witnessed at shallow depths. This observation could be attributed to higher in-situ stresses and virgin rock temperatures.
Originality. Major researches on the platinum mine have not extensively consider the influence of the increased temperature at the ultra-depth level hence this study aims to fill the gap by studying the effect of the increased temperature and stresses on the stability of stopes at the ultra-depth levels within the BIC.
Practical implications. This research showed that mining at ultra-deep levels would pose a challenge of an increase in horizontal and vertical displacements with increasing depth. It is recommended that horseshoe-shaped stopes could be preferred in such conditions to avoid high-stress concentration at the corners of the roof of the stopes, which may reduce failures from shallow-depth to ultra-depth levels. Also, based on the magnitude of convergence that will be experienced at ultra-deep mining levels (3500 to 5000 m), it is recommended that access development is located in the more competent strata, such as in mottled anorthosite with an average UCS of 82 MPa.
Keywords: temperature variation, numerical modelling, laboratory testing, Bushveld rocks, platinum mines
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