Reassessing continuous stope closure data using a limit equilibrium displacement discontinuity model

Abstract

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 timedependent 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.