Open stope design: state-of-the-art

Abstract

The stability graph method is the primary method for open stope design. The stability graph was introduced about three decades ago for bulk mining of orebodies below 1000-m depth. Since then, it has gained wide recognition around the world in hard rock metalliferous mining. Several developments aimed at improving its reliability in predicting the stability state of stopes have taken place. These developments include re-definition of the stability graph number factors, the transition zones, and addition of new factors. Various types of stability graphs have also emerged over the years for other purposes such as cablebolt layout design. The original database has also been significantly expanded from the original 26 cases in 1981 to 483 cases to date. This paper, critically reviews the developments of the stability graph to date with the objectives of:  Synthesizing the scattered knowledge of these developments in the literature to a single source.  Making potential users of the method aware of the problems and risks arising from the uncoordinated application of the method.  Identifying areas for further research to improve the reliability of the method; and finally  Providing guidelines to inexperienced users of the stability graph, and practitioners unaware of the various developments on when to use any one of the several stability graph types currently available. The paper stresses that as an empirical method, the reliability of the stability graph is largely dependent on the size, quality and consistency of the database. The present tendency for authors to arbitrarily choose between the original and modified stability number factors, result in incomparable data that cannot be combined, while the different transition zones result in different interpretations of the stability state of a given stope surface thereby creating confusion. The review also shows that there is need for factors that account for stope stand-up Proceedings of the first biennial UMaT International Conference on Mining & Mineral Processing, “Expanding the Frontiers of Mining Technology”, Tarkwa, Ghana, 4th – 7 th August, 2010. 2 time, blast damage, and a gravity factor that is stress factor dependent. There is also a need to develop procedures for determining stability of open stope surfaces that are made of backfill. The inexperienced user and practitioner unaware of the various versions of the stability graph should be conscious of the different versions and types of stability graphs in order to make the appropriate choice for his/her design. The stability graph should also be used with caution, when it is applied to narrow vein orebodies since no version of the graphs account for orebody thickness in the definitions of the stability states.