ABSTRACT: A method based on yield zone distribution to assess the stability of non-entry mine stopes in sublevel stoping with delayed backfill is presented. The method, based on nonlinear finite element modelling, is compared to the Stability Graph Method commonly in Canadian underground metal mines. It is shown that the stability of the stope walls is significantly affected by previous mining activities below the stope; an aspect which is not recognized by the empirical Stability Graph Method. Furthermore, numerical modelling helps identify the locations of maximum overbreak, whereas empirical methods don’t. The comparison of results for three mining depths namely 1500m, 2000m and 2500m is also presented and discussed.
1 INTRODUCTION
The sublevel stoping method with delayed backfill is one of the most popular mining methods in Canadian underground metal mines. In this method, as more ore is blasted and drawn from the stope, there is less rock mass to support the stope walls and hence there is the risk that the stope walls will cave or slough beyond the planned stope boundaries before the stope is completely mined out. When this occurs, the waste rock is mixed with the blasted ore in the mucking process and this would result in a reduction of the mill grade, hence causing adverse effects on the economics of the mining operation. A proper underground geomechanical mine design should ensure adequate stability of the nonentry stope walls during the life of the stope and until the stope has been mined out and backfilled. Mine stope stability in Canadian mines is traditionally carried out with the empirically-based Stability Graph Method (Potvin 1988), as illustrated in Figure 1. The Stability Graph Method is based on the Qsystem (Barton et al. 1974), originally developed by Mathews et al. (1980) and later modified by Potvin (1988).
