Abstract

MALAN, D.F.  and  NAPIER, J.A.L.. Reassessing continuous stope closure data using a limit equilibrium displacement discontinuity model. J. S. Afr. Inst. Min. Metall. [online]. 2018, vol.118, n.3, pp.227-234. ISSN 2411-9717.  https://doi.org/10.17159/2411-9717/2018/v118n3a5.

Time-dependent closure data in deep hard-rock mines appears to be a useful diagnostic measure of rock behaviour. Understanding this behaviour may lead to enhanced design criteria and modelling tools. This paper investigates the use of a time-dependent limit equilibrium model to simulate historical closure profiles collected in the South African mining industry. Earlier work indicated that a viscoelastic model is not suitable for replicating the spatial behaviour of the closure recorded underground. The time-dependent limit equilibrium model available in the TEXAN code appears to be a useful alternative as it can explicitly simulate the on-reef time-dependent failure of the reef. A key finding in this paper is that the model gives a much better qualitative agreement with the underground measurements. For both the model and actual data, the rate of time-dependent closure decreases into the back area. Calibration of the constitutive model nevertheless led to some unexpected difficulties, and element size plays a significant role. It was also noted that the simulated closure is complex as it reflects the combined result of a number of elements failing at different times. The closure rate does not decay according to a simple exponential model. Explicit simulation of the fracture zone in the face appears to be a better approach to simulating the time-dependent behaviour in deep hard-rock stopes. The calibration of the limit equilibrium model is very difficult, however, and further work is required.

Keywords : stope closure; time-dependent deformation; limit equilibrium model; TEXAN code.

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